Showing papers on "Perfusion scanning published in 2017"
TL;DR: A dual sequence for myocardial perfusion cardiovascular magnetic resonance and AIF measurement has been optimized for quantification of myocardia blood flow and reliable perfusion mapping was demonstrated and produced estimates with low variability.
Abstract: Quantification of myocardial blood flow requires knowledge of the amount of contrast agent in the myocardial tissue and the arterial input function (AIF) driving the delivery of this contrast agent. Accurate quantification is challenged by the lack of linearity between the measured signal and contrast agent concentration. This work characterizes sources of non-linearity and presents a systematic approach to accurate measurements of contrast agent concentration in both blood and myocardium. A dual sequence approach with separate pulse sequences for AIF and myocardial tissue allowed separate optimization of parameters for blood and myocardium. A systems approach to the overall design was taken to achieve linearity between signal and contrast agent concentration. Conversion of signal intensity values to contrast agent concentration was achieved through a combination of surface coil sensitivity correction, Bloch simulation based look-up table correction, and in the case of the AIF measurement, correction of T2* losses. Validation of signal correction was performed in phantoms, and values for peak AIF concentration and myocardial flow are provided for 29 normal subjects for rest and adenosine stress. For phantoms, the measured fits were within 5% for both AIF and myocardium. In healthy volunteers the peak [Gd] was 3.5 ± 1.2 for stress and 4.4 ± 1.2 mmol/L for rest. The T2* in the left ventricle blood pool at peak AIF was approximately 10 ms. The peak-to-valley ratio was 5.6 for the raw signal intensities without correction, and was 8.3 for the look-up-table (LUT) corrected AIF which represents approximately 48% correction. Without T2* correction the myocardial blood flow estimates are overestimated by approximately 10%. The signal-to-noise ratio of the myocardial signal at peak enhancement (1.5 T) was 17.7 ± 6.6 at stress and the peak [Gd] was 0.49 ± 0.15 mmol/L. The estimated perfusion flow was 3.9 ± 0.38 and 1.03 ± 0.19 ml/min/g using the BTEX model and 3.4 ± 0.39 and 0.95 ± 0.16 using a Fermi model, for stress and rest, respectively. A dual sequence for myocardial perfusion cardiovascular magnetic resonance and AIF measurement has been optimized for quantification of myocardial blood flow. A validation in phantoms was performed to confirm that the signal conversion to gadolinium concentration was linear. The proposed sequence was integrated with a fully automatic in-line solution for pixel-wise mapping of myocardial blood flow and evaluated in adenosine stress and rest studies on N = 29 normal healthy subjects. Reliable perfusion mapping was demonstrated and produced estimates with low variability.
259 citations
TL;DR: For the first time, it is shown that MPI could be used as a diagnostic tool for relevant diseases in vivo, such as an ischemic stroke, due to its shorter image acquisition times and increased temporal resolution compared to that of MRI or CT.
Abstract: The fast and accurate assessment of cerebral perfusion is fundamental for the diagnosis and successful treatment of stroke patients. Magnetic particle imaging (MPI) is a new radiation-free tomographic imaging method with a superior temporal resolution, compared to other conventional imaging methods. In addition, MPI scanners can be built as prehospital mobile devices, which require less complex infrastructure than computed tomography (CT) and magnetic resonance imaging (MRI). With these advantages, MPI could accelerate the stroke diagnosis and treatment, thereby improving outcomes. Our objective was to investigate the capabilities of MPI to detect perfusion deficits in a murine model of ischemic stroke. Cerebral ischemia was induced by inserting of a microfilament in the internal carotid artery in C57BL/6 mice, thereby blocking the blood flow into the medial cerebral artery. After the injection of a contrast agent (superparamagnetic iron oxide nanoparticles) specifically tailored for MPI, cerebral perfusi...
207 citations
University of California, Los Angeles1, Toronto Western Hospital2, University Hospitals of Cleveland3, Erlanger Health System4, WellStar Kennestone Hospital5, Rush University Medical Center6, University of California, San Francisco7, University of Nebraska Medical Center8, UCLA Medical Center9, West Virginia University Hospitals10, Yale University11, Emory University12
TL;DR: To establish whether subjects considered to have substantial areas of salvageable brain based on age-adjusted clinical core mismatch who can undergo endovascular treatment within 6–24 h from time last seen well (TLSW) have better outcomes at three months compared to subjects treated with standard medical therapy alone.
Abstract: Rationale Efficacy of mechanical thrombectomy for acute stroke due to large vessel occlusion initiated beyond 6 h of time last seen well has not been demonstrated in randomized trials. Aim To establish whether subjects considered to have substantial areas of salvageable brain based on age-adjusted clinical core mismatch who can undergo endovascular treatment within 6-24 h from time last seen well (TLSW) have better outcomes at three months compared to subjects treated with standard medical therapy alone. Age-adjusted clinical core mismatch is defined by age (≤80 or >80 years), baseline National Institutes of Health Stroke Scale (NIHSS) (10-20 or ≥21), and core size (0-20 cm3 in subjects older than 80 and, in subjects younger than 80, 0-30 cm3 with NIHSS 10-20 and 31-50 cm3 with NIHSS ≥21). Design Prospective, randomized, multicenter, Bayesian adaptive-enrichment, open label trial with blinded endpoint assessment. For the purpose of enrolment, ischemic core size will be evaluated by CT perfusion or magnetic resonance imaging-diffusion-weighted imaging measured by automated software (RAPID). Procedures Subjects with acute ischemic stroke due to computed tomography angiography- or magnetic resonance angiogram-proven arterial occlusion of the intracranial internal carotid and/or proximal middle cerebral artery (M1) with age-adjusted clinical core mismatch in whom treatment can be initiated between 6 and 24 h from TSLW are randomized in a 1:1 ratio to receive mechanical embolectomy with the Trevo device or medical management alone. Sequential interim analyses allowing adaptation of enrolment criteria or stopping new enrolment for futility or predicted success will occur in every 50 randomized patients starting at 150 to a maximum of 500 patients. Study outcomes The primary endpoint is the modified Rankin Scale score at 90 days. The primary safety outcome is stroke-related mortality at 90 days. Analysis The primary endpoint, expressed as a utility-weighted modified Rankin Scale score is analyzed using a Bayesian posterior probability with adjustment for ischemic core size. For regulatory reasons, a nested co-primary endpoint analysis was added consisting of the proportion of subjects with modified Rankin Scale 0-2 between the active and control groups also analyzed using a Bayesian model.
199 citations
TL;DR: Imaging plays a central role for intravenous and intra-arterial arterial ischemic stroke treatment patient selection and may identify the patients that will benefit more from revascularization therapies independently of the conventional therapeutic time window allowing individualized treatment decisions and improving individual patient outcome.
187 citations
TL;DR: Patients with cerebral large vessel occlusion who underwent CTP on admission but received endovascular thrombectomy based on a non-contrast CT Alberta Stroke Program Early CT Score (ASPECTS) >6.5 may not benefit from reperfusion therapies, and CT perfusion may overestimate final infarct core, especially in the early time window.
Abstract: Background Identifying infarct core on admission is essential to establish the amount of salvageable tissue and indicate reperfusion therapies. Infarct core is established on CT perfusion (CTP) as the severely hypoperfused area, however the correlation between hypoperfusion and infarct core may be time-dependent as it is not a direct indicator of tissue damage. This study aims to characterize those cases in which the admission core lesion on CTP does not reflect an infarct on follow-up imaging. Methods We studied patients with cerebral large vessel occlusion who underwent CTP on admission but received endovascular thrombectomy based on a non-contrast CT Alberta Stroke Program Early CT Score (ASPECTS) >6. Admission infarct core was measured on initial cerebral blood volume (CBV) CTP and final infarct on follow-up CT. We defined ghost infarct core (GIC) as initial core minus final infarct >10 mL. Results 79 patients were studied. Median National Institutes of Health Stroke Scale (NIHSS) score was 17 (11–20), median time from symptoms to CTP was 215 (87–327) min, and recanalization rate (TICI 2b–3) was 77%. Thirty patients (38%) presented with a GIC >10 mL. GIC >10 mL was associated with recanalization (TICI 2b–3: 90% vs 68%; p=0.026), admission glycemia ( 185 min: 26%; p=0.033). An adjusted logistic regression model identified time from symptom to CTP imaging 10 mL (OR 2.89, 95% CI 1.04 to 8.09). At 24 hours, clinical improvement was more frequent in patients with GIC >10 mL (66.6% vs 39%; p=0.017). Conclusions CT perfusion may overestimate final infarct core, especially in the early time window. Selecting patients for reperfusion therapies based on the CTP mismatch concept may deny treatment to patients who might still benefit from reperfusion.
164 citations
TL;DR: There is good agreement between MP quantified by 13N–NH3 PET and dual sequence, single contrast bolus CMR in patients with stable CAD, and CMR is viable in clinical practice for quantification of MP.
Abstract: Recent studies have shown that quantification of myocardial perfusion (MP) at stress and myocardial perfusion reserve (MPR) offer additional diagnostic and prognostic information compared to qualitative and semi-quantitative assessment of myocardial perfusion distribution in patients with coronary artery disease (CAD). Technical advancements have enabled fully automatic quantification of MP using cardiovascular magnetic resonance (CMR) to be performed in-line in a clinical workflow. The aim of this study was to validate the use of the automated CMR perfusion mapping technique for quantification of MP using 13N–NH3 cardiac positron emission tomography (PET) as the reference method. Twenty-one patients with stable CAD were included in the study. All patients underwent adenosine stress and rest perfusion imaging with 13N–NH3 PET and a dual sequence, single contrast bolus CMR on the same day. Global and regional MP were quantified both at stress and rest using PET and CMR. There was good agreement between global MP quantified by PET and CMR both at stress (−0.1 ± 0.5 ml/min/g) and at rest (0 ± 0.2 ml/min/g) with a strong correlation (r = 0.92, p < 0.001; y = 0.94× + 0.14). Furthermore, there was strong correlation between CMR and PET with regards to regional MP (r = 0.83, p < 0.001; y = 0.87× + 0.26) with a good agreement (−0.1 ± 0.6 ml/min/g). There was also a significant correlation between CMR and PET with regard to global and regional MPR (r = 0.69, p = 0.001 and r = 0.57, p < 0.001, respectively). There is good agreement between MP quantified by 13N–NH3 PET and dual sequence, single contrast bolus CMR in patients with stable CAD. Thus, CMR is viable in clinical practice for quantification of MP.
138 citations
TL;DR: Cardiac hybrid imaging relies on the fusion of anatomical and functional imaging using coronary computed tomography angiography and MPI, respectively, and provides incremental value as compared with either stand-alone modality.
Abstract: Noninvasive assessment of coronary artery disease remains a challenging task, with a large armamentarium of diagnostic modalities. Myocardial perfusion imaging (MPI) is widely used for this purpose whereby cardiac positron emission tomography (PET) is considered the gold standard. Next to relative radiotracer distribution, PET allows for measurement of absolute myocardial blood flow. This quantification of perfusion improves diagnostic accuracy and prognostic value. Cardiac hybrid imaging relies on the fusion of anatomical and functional imaging using coronary computed tomography angiography and MPI, respectively, and provides incremental value as compared with either stand-alone modality.
114 citations
TL;DR: The first high-contrast in vivo MPI lung perfusion images of rats are shown using a novel lung perfusions agent, MAA-SPIOs, enabling deep imaging of anatomy including within the lungs, which is very challenging with MRI.
Abstract: Pulmonary embolism (PE), along with the closely related condition of deep vein thrombosis, affect an estimated 600 000 patients in the US per year. Untreated, PE carries a mortality rate of 30%. Because many patients experience mild or non-specific symptoms, imaging studies are necessary for definitive diagnosis of PE. Iodinated CT pulmonary angiography is recommended for most patients, while nuclear medicine-based ventilation/perfusion (V/Q) scans are reserved for patients in whom the use of iodine is contraindicated. Magnetic particle imaging (MPI) is an emerging tracer imaging modality with high image contrast (no tissue background signal) and sensitivity to superparamagnetic iron oxide (SPIO) tracer. Importantly, unlike CT or nuclear medicine, MPI uses no ionizing radiation. Further, MPI is not derived from magnetic resonance imaging (MRI); MPI directly images SPIO tracers via their strong electronic magnetization, enabling deep imaging of anatomy including within the lungs, which is very challenging with MRI. Here, the first high-contrast in vivo MPI lung perfusion images of rats are shown using a novel lung perfusion agent, MAA-SPIOs.
114 citations
TL;DR: In patients with suspected stable CAD, a tiered cardiac CT protocol with dynamic perfusion imaging offers a fast and efficient alternative to functional testing.
Abstract: Objectives This study sought to assess the effectiveness, efficiency, and safety of a tiered, comprehensive cardiac computed tomography (CT) protocol in comparison with functional testing. Background Although CT angiography accurately rules out coronary artery disease (CAD), incorporation of CT myocardial perfusion imaging as part of a tiered diagnostic approach could improve the clinical value and efficiency of cardiac CT in the diagnostic work-up of patients with angina pectoris. Methods Between July 2013 and November 2015, 268 patients (mean age 58 years; 49% female) with stable angina (mean pre-test probability 54%) were prospectively randomized between cardiac CT and standard guideline-directed functional testing (95% exercise electrocardiography). The tiered cardiac CT protocol included a calcium scan, followed by CT angiography if calcium was detected. Patients with ≥50% stenosis on CT angiography underwent CT myocardial perfusion imaging. Results By 6 months, the primary endpoint, the rate of invasive coronary angiograms without a European Society of Cardiology class I indication for revascularization, was lower in the CT group than in the functional testing group (2 of 130 [1.5%] vs. 10 of 138 [7.2%]; p = 0.035), whereas the proportion of invasive angiograms with a revascularization indication was higher (88% vs. 50%; p = 0.017). The median duration until the final diagnosis was 0 (0 of 0) days in the CT group and 0 (0 of 17) in the functional testing group (p Conclusions In patients with suspected stable CAD, a tiered cardiac CT protocol with dynamic perfusion imaging offers a fast and efficient alternative to functional testing. (Comprehensive Cardiac CT Versus Exercise Testing in Suspected Coronary Artery Disease 2 [CRESCENT2]; NCT02291484)
112 citations
TL;DR: The most common clinical SM includes conversion/functional (psychiatric disorder); seizures and postictal paralysis; toxic-metabolic disturbances; brain tumours; infections, and migraine.
110 citations
TL;DR: Therapeutic ultrasound using microbubble cavitation to increase muscle perfusion relies on shear-dependent increases in ATP, which can act through a diverse portfolio of purinergic signaling pathways that can reverse hindlimb ischemia in mice for >24 hours and increase muscle blood flow in patients with sickle cell disease.
Abstract: Background: Augmentation of tissue blood flow by therapeutic ultrasound is thought to rely on convective shear. Microbubble contrast agents that undergo ultrasound-mediated cavitation markedly amplify these effects. We hypothesized that purinergic signaling is responsible for shear-dependent increases in muscle perfusion during therapeutic cavitation. Methods: Unilateral exposure of the proximal hindlimb of mice (with or without ischemia produced by iliac ligation) to therapeutic ultrasound (1.3 MHz, mechanical index 1.3) was performed for 10 minutes after intravenous injection of 2×10 8 lipid microbubbles. Microvascular perfusion was evaluated by low-power contrast ultrasound perfusion imaging. In vivo muscle ATP release and in vitro ATP release from endothelial cells or erythrocytes were assessed by a luciferin-luciferase assay. Purinergic signaling pathways were assessed by studying interventions that (1) accelerated ATP degradation; (2) inhibited P2Y receptors, adenosine receptors, or K ATP channels; or (3) inhibited downstream signaling pathways involving endothelial nitric oxide synthase or prostanoid production (indomethacin). Augmentation in muscle perfusion by ultrasound cavitation was assessed in a proof-of-concept clinical trial in 12 subjects with stable sickle cell disease. Results: Therapeutic ultrasound cavitation increased muscle perfusion by 7-fold in normal mice, reversed tissue ischemia for up to 24 hours in the murine model of peripheral artery disease, and doubled muscle perfusion in patients with sickle cell disease. Augmentation in flow extended well beyond the region of ultrasound exposure. Ultrasound cavitation produced an ≈40-fold focal and sustained increase in ATP, the source of which included both endothelial cells and erythrocytes. Inhibitory studies indicated that ATP was a critical mediator of flow augmentation that acts primarily through either P2Y receptors or adenosine produced by ectonucleotidase activity. Combined indomethacin and inhibition of endothelial nitric oxide synthase abolished the effects of therapeutic ultrasound, indicating downstream signaling through both nitric oxide and prostaglandins. Conclusions: Therapeutic ultrasound using microbubble cavitation to increase muscle perfusion relies on shear-dependent increases in ATP, which can act through a diverse portfolio of purinergic signaling pathways. These events can reverse hindlimb ischemia in mice for >24 hours and increase muscle blood flow in patients with sickle cell disease. Clinical Trial Registration: URL: http://clinicaltrials.gov. Unique identifier: NCT01566890.
TL;DR: A theory of ‘deep MRI physiotyping’ is inferred from the combined knowledge of factors influencing brain perfusion as a strategy to reduce variance by taking both personal information and the presence or absence of perfusion modifiers into account.
Abstract: Quantitative measurements of brain perfusion are influenced by perfusion-modifiers. Standardization of measurement conditions and correction for important modifiers is essential to improve accuracy and to facilitate the interpretation of perfusion-derived parameters. An extensive literature search was carried out for factors influencing quantitative measurements of perfusion in the human brain unrelated to medication use. A total of 58 perfusion modifiers were categorized into four groups. Several factors (e.g., caffeine, aging, and blood gases) were found to induce a considerable effect on brain perfusion that was consistent across different studies; for other factors, the modifying effect was found to be debatable, due to contradictory results or lack of evidence. Using the results of this review, we propose a standard operating procedure, based on practices already implemented in several research centers. Also, a theory of ‘deep MRI physiotyping’ is inferred from the combined knowledge of factors influencing brain perfusion as a strategy to reduce variance by taking both personal information and the presence or absence of perfusion modifiers into account. We hypothesize that this will allow to personalize the concept of normality, as well as to reach more rigorous and earlier diagnoses of brain disorders.
TL;DR: In this paper, the authors evaluated how predefined candidate cerebral perfusion parameters correlate with collateral circulation status and assessed their capacity to predict infarct growth in patients with acutal lesions.
Abstract: We aimed to evaluate how predefined candidate cerebral perfusion parameters correlate with collateral circulation status and to assess their capacity to predict infarct growth in patients with acut...
TL;DR: The accuracy of various rCBV and rCBF thresholds for predicting the 27-hour infarct volume was analyzed using RAPID automated analysis software from the SWIFT PRIME trial data to find the most accurate thresholds.
Abstract: Background and Purpose— Computed tomography perfusion imaging can estimate the size of the ischemic core, which can be used for the selection of patients for endovascular therapy. The relative cerebral blood volume (rCBV) and relative cerebral blood flow (rCBF) thresholds chosen to identify ischemic core influence the accuracy of prediction. We aimed to analyze the accuracy of various rCBV and rCBF thresholds for predicting the 27-hour infarct volume using RAPID automated analysis software from the SWIFT PRIME trial (Solitaire With the Intention for Thrombectomy as Primary Endovascular Treatment) data.
Methods— Patients from the SWIFT PRIME study who achieved complete reperfusion based on time until the residue function reached its peak >6 s perfusion maps obtained at 27 hours were included. Patients from both the intravenous tissue-type plasminogen activator only and endovascular groups were included in analysis. Final infarct volume was determined on magnetic resonance imaging (fluid-attenuated inversion recovery images) or computed tomography scans obtained 27 hours after symptom onset. The predicted ischemic core volumes on rCBV and rCBF maps using thresholds ranging between 0.2 and 0.8 were compared with the actual infarct volume to determine the most accurate thresholds.
Results— Among the 47 subjects, the following baseline computed tomography perfusion thresholds most accurately predicted the actual 27-hour infarct volume: rCBV=0.32, median absolute error (MAE)=9 mL; rCBV=0.34, MAE=9 mL; rCBF=0.30, MAE=8.8 mL; rCBF=0.32, MAE=7 mL; and rCBF=0.34, MAE=7.3.
Conclusions— Brain regions with rCBF 0.30 to 0.34 or rCBV 0.32 to 0.34 thresholds provided the most accurate prediction of infarct volume in patients who achieved complete reperfusion with MAEs of ≤9 mL.
Clinical Trial Registration— URL: . Unique identifier: [NCT01657461][1].
[1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT01657461&atom=%2Fstrokeaha%2F48%2F4%2F932.atom
TL;DR: Whether cortical microvascular blood volume and hemodynamics in Alzheimer's disease (AD) are consistent with tissue hypoxia and whether they correlate with cognitive performance and the degree of cortical thinning is examined.
Abstract: Introduction We examined whether cortical microvascular blood volume and hemodynamics in Alzheimer's disease (AD) are consistent with tissue hypoxia and whether they correlate with cognitive performance and the degree of cortical thinning. Methods Thirty-two AD patients underwent cognitive testing, structural magnetic resonance imaging (MRI), and perfusion MRI at baseline and after 6 months. We measured cortical thickness, microvascular cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), and capillary transit time heterogeneity (CTH) and estimated tissue oxygen tension (P t O 2 ). Results At baseline, poor cognitive performance and regional cortical thinning correlated with lower CBF and CBV, with higher MTT and CTH and with low P t O 2 across the cortex. Cognitive decline over time was associated with increasing whole brain relative transit time heterogeneity (RTH = CTH/MTT). Discussion Our results confirm the importance of microvascular pathology in AD. Deteriorating microvascular hemodynamics may cause hypoxia, which is known to precipitate amyloid retention.
TL;DR: Test-retest methodological precision of global PET myocardial perfusion by serial rest or stress PET minutes apart is ±10%, thereby establishing boundaries of variability on physiological severity to guide or follow coronary artery disease management.
Abstract: Objectives Positron emission tomography (PET) quantifies stress myocardial perfusion (in cc/min/g) and coronary flow reserve to guide noninvasively the management of coronary artery disease. This study determined their test-retest precision within minutes and daily biological variability essential for bounding clinical decision-making or risk stratification based on low flow ischemic thresholds or follow-up changes. Background Randomized trials of fractional flow reserve–guided percutaneous coronary interventions established an objective, quantitative, outcomes-driven standard of physiological stenosis severity. However, pressure-derived fractional flow reserve requires invasive coronary angiogram and was originally validated by comparison to noninvasive PET. Methods The time course and test-retest precision of serial quantitative rest-rest and stress-stress global myocardial perfusion by PET within minutes and days apart in the same patient were compared in 120 volunteers undergoing serial 708 quantitative PET perfusion scans using rubidium 82 (Rb-82) and dipyridamole stress with a 2-dimensional PET-computed tomography scanner (GE DST 16) and University of Texas HeartSee software with our validated perfusion model. Results Test-retest methodological precision (coefficient of variance) for serial quantitative global myocardial perfusion minutes apart is ±10% (mean ΔSD at rest ±0.09, at stress ±0.23 cc/min/g) and for days apart is ±21% (mean ΔSD at rest ±0.2, at stress ±0.46 cc/min/g) reflecting added biological variability. Global myocardial perfusion at 8 minutes after 4-min dipyridamole infusion is 10% higher than at standard 4 min after dipyridamole. Conclusions Test-retest methodological precision of global PET myocardial perfusion by serial rest or stress PET minutes apart is ±10%. Day-to-different-day biological plus methodological variability is ±21%, thereby establishing boundaries of variability on physiological severity to guide or follow coronary artery disease management. Maximum stress increases perfusion and coronary flow reserve, thereby reducing potentially falsely low values mimicking ischemia.
TL;DR: The basic concepts in ASL are reviewed and the current state-of-the-art acquisition and analysis approaches are described, and the versatility of the method to perform both quantitative cerebral perfusion measurement, along with quantitative cerebral angiographic measurement is described.
Abstract: Arterial spin labeling (ASL) is an MRI technique that was first proposed a quarter of a century ago. It offers the prospect of non-invasive quantitative measurement of cerebral perfusion, making it potentially very useful for research and clinical studies, particularly where multiple longitudinal measurements are required. However, it has suffered from a number of challenges, including a relatively low signal-to-noise ratio, and a confusing number of sequence variants, thus hindering its clinical uptake. Recently, however, there has been a consensus adoption of an accepted acquisition and analysis framework for ASL, and thus a better penetration onto clinical MRI scanners. Here, we review the basic concepts in ASL and describe the current state-of-the-art acquisition and analysis approaches, and the versatility of the method to perform both quantitative cerebral perfusion measurement, along with quantitative cerebral angiographic measurement.
TL;DR: The aim of this article is to review the current published evidence on the feasibility of in vivo perfusion imaging with intravoxel incoherent motion MRI and to praise the tremendous improvements seen in the last three decades in MR hardware, pulse design, and post‐processing capabilities.
Abstract: The idea that in vivo intravoxel incoherent motion magnetic resonance signal is influenced by blood motion in the microvasculature is exciting, because it suggests that local and quantitative perfusion information can be obtained in a simple and elegant way from a few diffusion-weighted images, without contrast injection. When the method was proposed in the late 1980s some doubts appeared as to its feasibility, and, probably because the signal to noise and image quality at the time was not sufficient, no obvious experimental evidence could be produced to alleviate them. Helped by the tremendous improvements seen in the last three decades in MR hardware, pulse design, and post-processing capabilities, an increasing number of encouraging reports on the value of intravoxel incoherent motion perfusion imaging have emerged. The aim of this article is to review the current published evidence on the feasibility of in vivo perfusion imaging with intravoxel incoherent motion MRI.
TL;DR: The analyses demonstrate consistency with both the hyperfrontal hypothesis of psilocybin and the more recent study demonstrating decreased perfusion, depending on analysis method, and highlight the importance of evaluating regional and global CBF.
TL;DR: Correlation analyses revealed that in patients, hypoperfusion in PCC and precuneus regions were related to higher insulin resistance level and deficits in clock-drawing performance, while the occipital hypoperFusion was associated with worse visual-memory performance, regardless of PVEs correction.
Abstract: To explore the effect of T2DM on cerebral perfusion, and the relationship between cerebral perfusion changes and cognitive impairment as well as diabetic variables, by using a whole-brain arterial spin-labeling (ASL) MRI technique. This prospective study was approved by the local institutional review board and was performed between November 2012 and October 2013. All subjects provided informed consent. Forty T2DM patients and 41 age-, sex- and education-matched healthy controls were included. Cerebral blood flow (CBF) map was obtained by pulsed ASL perfusion imaging at 3 T MRI. Voxel-wise comparisons on CBF maps with and without partial volume effects (PVEs) correction were performed between groups. Associations between CBF and cognitive functioning, and between CBF and diabetic variables were investigated by using voxel-wise, whole-brain correlation analyses. In T2DM patients, PVEs uncorrected CBF was decreased in the posterior cingulate cortex (PCC), precuneus and bilateral occipital lobe, and increased in the anterior cingulate cortex (corrected P < .05). These changes were largely unchanged after PVEs correction. Correlation analyses revealed that in patients, hypoperfusion in PCC and precuneus regions were related to higher insulin resistance level and deficits in clock-drawing performance, while the occipital hypoperfusion was associated with worse visual-memory performance, regardless of PVEs correction. The cerebral hypoperfusion pattern in T2DM resembles the pattern observed in the early stage of dementia, and increased insulin resistance might be an important risk factor as well as treatment target for such CBF dysregulation.
National Institutes of Health1, University of São Paulo2, Johns Hopkins University3, Charité4, Iwate Medical University5, Mie University6, Beth Israel Deaconess Medical Center7, University of Copenhagen8, Keio University9, Leiden University Medical Center10, Mount Elizabeth Hospital11, Toronto General Hospital12, University of Ottawa13, Brigham and Women's Hospital14
TL;DR: Combined CT angiography and CT perfusion enables similar prediction of 2-year Mace, late MACE, and event-free survival similar to that enabled by ICA and single photon emission CT.
Abstract: Combined CT angiography and CT myocardial perfusion enables similar prediction of 2-year major adverse cardiovascular event–free survival, including the need for myocardial revascularization procedures, similar to that achieved with standard invasive coronary angiography and single photon emission CT perfusion imaging.
TL;DR: In patients with suspected CAD obstructive disease can be excluded in 53% of patients by coronary CTA, and these patients have good outcome, and about one-half of the remaining patients have normal perfusion and event rate comparable to patients without obstructive CAD on coronary CTA while patients with ischemia have clearly worse outcome.
Abstract: Objectives The purpose of this study was to evaluate the prognostic value of sequential hybrid imaging strategy in which positron emission tomography (PET) perfusion imaging is performed selectively in patients with suspected obstructive coronary artery disease (CAD) on coronary computed tomography angiography (CTA). Background Coronary CTA is an accurate diagnostic test for excluding obstructive CAD. However, the positive predictive value is suboptimal. Methods We investigated 864 consecutive symptomatic patients with intermediate probability of CAD who adhered to the sequential imaging approach. PET myocardial perfusion imaging using 15O-labeled water during adenosine stress was performed when suspected obstructive stenosis was present on coronary CTA. The major adverse events (AEs) including all-cause mortality, myocardial infarction (MI), and unstable angina pectoris (UAP) were recorded. Results During a median follow-up of 3.6 years, 16 deaths, 10 MIs, and 5 UAPs occurred. Obstructive CAD was excluded by coronary CTA in 462 (53%) patients who had significantly lower annual AE rate than did patients with suspected obstructive stenosis on coronary CTA (0.4% vs. 1.5%; p = 0.003). The latter underwent PET study, on which 195 (49%) had normal and 207 had abnormal perfusion. The annual rate of AEs was 5 times higher in those with abnormal perfusion than with normal perfusion (2.5% vs. 0.5%; p = 0.004). Patients with normal perfusion had AE rate comparable to patients without obstructive CAD on coronary CTA (p = 0.77). Conclusions In patients with suspected CAD obstructive disease can be excluded in 53% of patients by coronary CTA, and these patients have good outcome. About one-half (49%) of the remaining patients have normal perfusion and event rate comparable to patients without obstructive CAD on coronary CTA while patients with ischemia have clearly worse outcome. Sequential approach utilizing anatomical imaging by coronary CTA followed by selective functional perfusion imaging is a feasible strategy to diagnose and risk-stratify patients with suspected CAD.
TL;DR: Lung perfusion alterations at DECT are less frequent and more homogeneous in PAH than in pCTEPH, with a high level of concordant findings with V/Q scintigraphy.
Abstract: To compare lung perfusion in PAH and pCTEPH on dual-energy CT (DECT) examinations. Thirty-one patients with PAH (group 1; n = 19) and pCTEPH (group 2; n = 12) underwent a dual-energy chest CTA with reconstruction of diagnostic and perfusion images. Perfusion alterations were analysed at a segmental level. V/Q scintigraphy was available in 22 patients (group 1: 13/19; group 2: 9/12). CT perfusion was abnormal in 52.6 % of group 1 patients and in 100 % of group 2 patients (p = 0.0051). The patterns of perfusion alteration significantly differed between the two groups (p < 0.0001): (1) in group 1, 96.6 % of segments with abnormal perfusion showed patchy defects; (2) in group 2, the most frequent abnormalities consisted of patchy (58.5 %) and PE-type (37.5 %) defects. Paired comparison of CT perfusion and scintigraphy showed concordant findings in 76.9 % of group 1 (10/13) and 100 % of group 2 (9/9) patients, with a predominant or an exclusive patchy pattern in group 1 and a mixed pattern of abnormalities in group 2. Lung perfusion alterations at DECT are less frequent and more homogeneous in PAH than in pCTEPH, with a high level of concordant findings with V/Q scintigraphy. • Depiction of chronic pulmonary embolism exclusively located on peripheral arteries is difficult.
• The main differential diagnosis of pCTEPH is PAH.
• The pattern of DECT perfusion changes can help differentiate PAH and pCETPH.
• In PAH, almost all segments with abnormal perfusion showed patchy defects.
• In pCTEPH, patchy and PE-type defects were the most frequent abnormalities.
TL;DR: In this article, the authors compared different analysis approaches to diagnose ischemia in patients with stable angina referred for invasive coronary angiography, using a second-generation dual-source scanner.
Abstract: Background— The clinical analysis of myocardial dynamic computed tomography myocardial perfusion imaging lacks standardization. The objective of this prospective study was to compare different analysis approaches to diagnose ischemia in patients with stable angina referred for invasive coronary angiography. Methods and Results— Patients referred for evaluation of stable angina symptoms underwent adenosine-stress dynamic computed tomography myocardial perfusion imaging with a second-generation dual-source scanner. Quantitative perfusion parameters, such as blood flow, were calculated by parametric deconvolution for each myocardial voxel. Initially, perfusion parameters were extracted according to standard 17-segment model of the left ventricle (fully automatic analysis). These were then manually sampled by an operator (semiautomatic analysis). Areas under the receiver-operating characteristic curves of the 2 different approaches were compared. Invasive fractional flow reserve ≤0.80 or diameter stenosis ≥80% on quantitative coronary angiography was used as reference standard to define ischemia. We enrolled 115 patients (88 men; age 57±9 years). There were 72 of 286 (25%) vessels causing ischemia in 52 of 115 (45%) patients. The semiautomatic analysis method was better than the fully automatic method at predicting ischemia (areas under the receiver-operating characteristic curves, 0.87 versus 0.69; P P P =ns). Conclusions— Endocardial perfusion parameters obtained by semiautomatic analysis of dynamic computed tomography myocardial perfusion imaging may permit robust discrimination between coronary vessels causing ischemia versus not causing ischemia.
TL;DR: CTP is more accurate than NCCT and has similar accuracy to CTA in detecting acute ischemic stroke, however, the evidence is not strong.
Abstract: Objective
To systematically evaluate and compare the diagnostic accuracy of CT perfusion (CTP), non-enhanced computed tomography (NCCT) and computed tomography angiography (CTA) in detecting acute ischemic stroke.
Methods
We searched seven databases and screened the reference lists of the included studies. The risk of bias in the study quality was assessed using QUADASII. We produced paired forest plots in RevMan to show the variation of the sensitivity and specificity estimates together with their 95% CI. We used a hierarchical summary ROC model to summarize the sensitivity and specificity of CTP in detecting ischemic stroke.
Results
We identified 27 studies with a total of 2168 patients. The pooled sensitivity of CTP for acute ischemic stroke was 82% (95% CI 75–88%), and the specificity was 96% (95% CI 89–99%). CTP was more sensitive than NCCT and had a similar accuracy with CTA. There were no statistically significant differences in the sensitivity and specificity between patients who underwent CTP within 6 hours of symptom onset and beyond 6 hours after symptom onset. No adverse events were reported in the included studies.
Conclusions
CTP is more accurate than NCCT and has similar accuracy to CTA in detecting acute ischemic stroke. However, the evidence is not strong. There is potential benefit of using CTP to select stroke patients for treatment, but more high-quality evidence is needed to confirm this result.
TL;DR: The factors which influence contrast enhancement are outlined, and an overview of current contrast injection and acquisition protocols are given, with focus on current emerging topics such as pre-transcatheter aortic valve replacement (TAVR) planning, cardiac CT for congenital heart disease patients, and myocardial CT perfusion (CTP).
Abstract: Cardiac computed tomography (CT) imaging has become an important part of modern cardiovascular care. Coronary CT angiography (CTA) is the first choice imaging modality for non-invasive visualization of coronary artery stenosis. In addition, cardiac CT does not only provide anatomical evaluation, but also functional and valvular assessment, and myocardial perfusion evaluation. In this article we outline the factors which influence contrast enhancement, give an overview of current contrast injection and acquisition protocols, with focus on current emerging topics such as pre-transcatheter aortic valve replacement (TAVR) planning, cardiac CT for congenital heart disease (CHD) patients, and myocardial CT perfusion (CTP). Further, we point out areas where we see potential for future improvements in cardiac CT imaging based on a closer interaction between CT scanner settings and contrast injection protocols to tailor injections to patient- and exam-specific factors.
TL;DR: It is indicated that increased BPV is associated with worse neurological outcome after stroke, particularly in patients with a large lesion core volume, concurrent viable ischaemic penumbra, proximal vessel occlusion and good collaterals, who may benefit from interventions aimed at reducing BPV.
Abstract: Introduction Increased blood pressure variability (BPV) is detrimental after acute ischaemic stroke, but the interaction between BPV and neuroimaging factors that directly influence stroke outcome has not been explored. Methods We retrospectively reviewed inpatients from 2007 to 2014 with acute anterior circulation ischaemic stroke, CT perfusion and angiography at hospital admission, and a modified Rankin Scale (mRS) 30–365 days after stroke onset. BPV indices included SD, coefficient of variation and successive variation of the systolic blood pressure between 0 and 120 hours after admission. Ordinal logistic regression models were fitted to mRS with predictor variables of BPV indices. Models were further stratified by CT perfusion volumetric measurements, proximal vessel occlusion and collateral score. Results 110 patients met the inclusion criteria. The likelihood of a 1-point rise in the mRS increased with every 10 mm Hg increase in BPV (OR for the 3 BPV indices ranged from 2.27 to 5.54), which was more pronounced in patients with larger ischaemic core volumes (OR 8.37 to 18.0) and larger hypoperfused volumes (OR 6.02 to 15.4). This association also held true for patients with larger mismatch volume, proximal vessel occlusion and good collateral vessels. Conclusions These results indicate that increased BPV is associated with worse neurological outcome after stroke, particularly in patients with a large lesion core volume, concurrent viable ischaemic penumbra, proximal vessel occlusion and good collaterals. This subset of patients, who are often not candidates for or fail acute stroke therapies such as intravenous tissue plasminogen activator or endovascular thrombectomy, may benefit from interventions aimed at reducing BPV.
TL;DR: Adenosine stress and rest splenic T1-mapping is a novel method for assessing stress responses, independent of conventional hemodynamic parameters, that enables prediction of the visual “splenic switch-off” sign without the need for gadolinium and correlates well to changes in splenic signal intensity during stress/rest perfusion imaging.
Abstract: Perfusion cardiovascular magnetic resonance (CMR) performed with inadequate adenosine stress leads to false-negative results and suboptimal clinical management. The recently proposed marker of adequate stress, the “splenic switch-off” sign, detects splenic blood flow attenuation during stress perfusion (spleen appears dark), but can only be assessed after gadolinium first-pass, when it is too late to optimize the stress response. Reduction in splenic blood volume during adenosine stress is expected to shorten native splenic T1, which may predict splenic switch-off without the need for gadolinium. Two-hundred and twelve subjects underwent adenosine stress CMR: 1.5 T (n = 104; 75 patients, 29 healthy controls); 3 T (n = 108; 86 patients, 22 healthy controls). Native T1spleen was assessed using heart-rate-independent ShMOLLI prototype sequence at rest and during adenosine stress (140 μg/kg/min, 4 min, IV) in 3 short-axis slices (basal, mid-ventricular, apical). This was compared with changes in peak splenic perfusion signal intensity (ΔSIspleen) and the “splenic switch-off” sign on conventional stress/rest gadolinium perfusion imaging. T1spleen values were obtained blinded to perfusion ΔSIspleen, both were derived using regions of interest carefully placed to avoid artefacts and partial-volume effects. Normal resting splenic T1 values were 1102 ± 66 ms (1.5 T) and 1352 ± 114 ms (3 T), slightly higher than in patients (1083 ± 59 ms, p = 0.04; 1295 ± 105 ms, p = 0.01, respectively). T1spleen decreased significantly during adenosine stress (mean ΔT1spleen ~ −40 ms), independent of field strength, age, gender, and cardiovascular diseases. While ΔT1spleen correlated strongly with ΔSIspleen (rho = 0.70, p < 0.0001); neither indices showed significant correlations with conventional hemodynamic markers (rate pressure product) during stress. By ROC analysis, a ΔT1spleen threshold of ≥ −30 ms during stress predicted the “splenic switch-off” sign (AUC 0.90, p < 0.0001) with sensitivity (90%), specificity (88%), accuracy (90%), PPV (98%), NPV (42%). Adenosine stress and rest splenic T1-mapping is a novel method for assessing stress responses, independent of conventional hemodynamic parameters. It enables prediction of the visual “splenic switch-off” sign without the need for gadolinium, and correlates well to changes in splenic signal intensity during stress/rest perfusion imaging. ΔT1spleen holds promise to facilitate optimization of stress responses before gadolinium first-pass perfusion CMR.
TL;DR: Hyperpolarized 129Xe MR imaging is an injection-free means of imaging the perfusion of cerebral tissue and images the uptake of inhaled xenon gas to the extravascular brain tissue compartment across the intact blood-brain barrier.
Abstract: The feasibility of directly imaging the uptake of xenon by the human brain following perfusion and gas transfer across the blood-brain barrier has been demonstrated by using inhaled hyperpolarized xenon 129 MR imaging.
TL;DR: Current evidence confirms the effectiveness of FDG-PET and sMRI for prediction of AD dementia in MCI, but there are discordant results regarding which image modality is superior, and perfusion SPECT is confirmed as a valid alternative whenFDG- PET is not available.
Abstract: This review article aims at providing a state-of-the-art review of the role of fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging (FDG-PET) in the prediction of Alzheimer's dementia in subjects suffering mild cognitive impairment (MCI), with a particular focus on the predictive power of FDG-PET compared to structural magnetic resonance imaging (sMRI). We also address perfusion single photon emission computed tomography (SPECT) as a less costly and more accessible alternative to FDG-PET. A search in PubMed was performed, taking into consideration relevant scientific articles published in English within the last five years and limited to human studies. This recent literature confirms the effectiveness of FDG-PET and sMRI for prediction of AD dementia in MCI. However, there are discordant results regarding which image modality is superior. This could be explained by the high variability of metrics used to evaluate both imaging modalities and/or by sampling/population issues such as age, disease severity and conversion time. FDG-PET seems to outperform sMRI in rapidly converting early-onset MCI individuals, whereas sMRI may outperform FDG-PET in late-onset MCI subjects, in which case FDG PET might only provide a complementary role. Although FDG-PET performs better than perfusion SPECT, current evidence confirms perfusion SPECT as a valid alternative when FDG- PET is not available. Finally, possible future directions in the field are discussed.