Abstract: Background—Diffuse coronary atherosclerosis is the substrate for plaque rupture and coronary events. Therefore, in patients with mild arteriographic coronary artery disease without significant segm...

Abstract: Perfusion imaging by arterial spin labeling (ASL) can be highly sensitive to the transit time from the labeling site to the tissue. We report the results of a study designed to separate the transit time and perfusion contributions to activation in ASL images accompanying motor and visual stimulation. Fractional transit time decreases were found to be comparable to fractional perfusion increases and the transit time change was found to be the greatest contributor to ASL signal change in ASL sequences without delayed acquisition. The implications for activation imaging with ASL and the arterial control of flow are discussed.

Abstract: Among exercise-independent stresses, the most popular are dobutamine and dipyridamole. Dobutamine is the prototype of pharmacological adrenergic or isotropic stresses, initially proposed in combination with perfusion imaging [1] and later with 2-D echocardiography [2, 3]. Other sympathomimetic agents have been proposed for stress echocardiography, including isoproterenol [4] and epinephrine [5], but arrhythmogenic side effects are frequent with these drugs. Dobutamine was first proposed in 1984 [1, 2] and later abandoned, mostly due to concern about induced arrhythmias [6]. In the past few years it has been extensively adopted as the most-used pharmacological stress — with an explosion triggered by the demonstration of low-dose dobutamine as a way to unmask myocardial viability by recruiting the inotropic reserve [7]. The main differences between physical and pharmacological stress echocardiography are summarized in Table 1.

Abstract: Transit time and trailing time in pulsed spin-labeling perfusion imaging are likely to be modulated by local blood flow changes, such as those accompanying brain activation. The majority of transit/trailing time is due to the passage of the tagged blood bolus through the arteriole/capillary regions, because of lower blood flow velocity in these regions. Changes of transit/trailing time during activation could affect the quantification of CBF in functional neuroimaging studies, and are therefore important to characterize. In this work, the measurement of transit and trailing times and CBF during sensorimotor activation using multislice perfusion imaging with pulsed arterial spin-labeling is described. While CBF elevated dramatically (∼80.7%) during the sensorimotor activation, sizable reductions of transit time (∼0.11 sec) and trailing time (∼0.26 sec) were observed. Transit and trailing times were dependent on the distances from the leading and trailing edges of the tagged blood bolus to the location of the imaging slices. The effects of transit/trailing time changes on CBF quantification during brain activation were analyzed by simulation studies. Significant errors can be caused in the estimation of CBF if such changes of transit/trailing time are not taken into account. Magn Reson Med 44:680–685, 2000. © 2000 Wiley-Liss, Inc.

Abstract: Here we present a method for measuring the permeability coefficient-surface area product (PS) values at the blood-brain barrier in mice, using the in situ brain perfusion technique originally developed for rats by Takasato et al. (Am J Physiol Heart Circ Physiol 247: H484-H493, 1984). Retrograde infusion into the right external carotid artery increased the carotid perfusion pressure in proportion to the perfusion rate. Intravascular volume and cerebral perfusion fluid flow at a perfusion rate of 1.0 ml/min in mice were similar to those in rats. In addition, the contribution of systemic blood to total flow in the hemisphere was small (only 3. 2%). These findings indicated that this perfusion rate is suitable for mice. The PS values of more than 20 different compounds were determined in mice by using the in situ brain perfusion technique, and comparisons were made with data from rats. There was a close relationship (1:1) between the PS values in mice and rats, indicating that brain capillary permeabilities are similar in mice and rats.

Abstract: Background and Purpose—Recent advances in neuroimaging have raised hopes of early and accurate identification of ischemic brain and the discrimination of dead from salvageable tissue. We sought to determine whether the data published so far are enough to establish the roles of these techniques in everyday clinical practice. Methods—A systematic review of studies of MR diffusion-weighted imaging (DWI), perfusion imaging (PI), or a combination of the two, in human stroke, excluding abstracts and case reports. One reviewer extracted information on the size of each study, its main purpose, methodological details, and results. Results—We identified 47 studies of DWI, 18 studies of MR PI alone or in combination with another advanced imaging modality, and 19 studies of DWI and PI together. Although high proportions of the studies were prospective and gave good details of the imaging sequences used, the majority gave very limited details on patient selection and clinical characteristics or blinded imaging assessm...

Abstract: Magnetic resonance (MR) and computed tomographic (CT) perfusion imaging are evolving noninvasive imaging techniques that, unlike conventional MR and CT angiographic methods, can be used to evaluate capillary level tissue perfusion. These techniques can provide early, highly accurate delineation of ischemic tissue, allowing the underlying hemodynamic disturbances of disorders such as stroke and vasospasm to be further analyzed, as well as defining abnormal regions of blood pool in brain tumors. Because MR perfusion (MRP) and CT perfusion (CTP) imaging can assess physiologic parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT), they offer additional data that can be useful in the detection and characterization of entities such as tumor, infection, inflammation, and infarction, which all can have similar appearances on both contrast and noncontrast enhanced conventional CT and MR images. They can also facilitate the further evaluation of processes such as early dementia, psychiatric illnesses, and migraine headaches, which may appear normal on routine CT and MR imaging. MRP and CTP might also be of value in distinguishing residual or recurrent tumor from treatment effects such as radiation-induced necrosis. This article reviews the background principles, scanning techniques, and clinical applications of noninvasive cerebral perfusion imaging.

Abstract: PURPOSE: To evaluate the diagnostic value of an imaging protocol that combines dynamic contrast-enhanced T1-weighted magnetic resonance (MR) imaging and T2*-weighted first-pass perfusion imaging in patients with breast tumors and to determine if T2*-weighted imaging can provide additional diagnostic information to that obtained with T1-weighted imaging. MATERIALS AND METHODS: One hundred thirty patients with breast tumors underwent MR imaging with dynamic contrast-enhanced T1-weighted imaging of the entire breast, which was followed immediately with single-section, T2*-weighted imaging of the tumor. RESULTS: With T2*-weighted perfusion imaging, 57 of 72 carcinomas but only four of 58 benign lesions had a signal intensity loss of 20% or more during the first pass, for a sensitivity of 79% and a specificity of 93%. With dynamic contrast-enhanced T1-weighted imaging, 64 carcinomas and 19 benign lesions showed a signal intensity increase of 90% or more in the first image obtained after the administration of c...

Abstract: Background Stroke management would benefit from a broadly available imaging tool that detects perfusion deficits in patients with acute stroke. Objective To determine the role of dynamic, single-slice computed tomographic (CT) perfusion imaging (CTP) in the assessment of acute middle cerebral artery stroke. Design and Patients Imaging with CTP and CT within the first 6 hours of symptom onset and before the start of treatment in a consecutive clinical series of 22 patients (mean age, 68.3 years; 14 women; studied within 143 ± 96 minutes of stroke onset). Setting A stroke unit in a university hospital. Main Outcome Measures Area of the perfusion deficit (nAP 0 ) from time-to-peak maps, hemispheric lesion area from follow-up CT (HLA F ), final infarct volume, and stroke recovery (National Institutes of Health Stroke Scale scores). Results Eighteen patients had perfusion deficits in the middle cerebral artery territory and corresponding hypoattenuation in follow-up CT. Three patients with normal CTP findings showed lacunar infarctions or normal findings on follow-up CT. In 1 patient, CTP did not reveal a territorial deficit above the imaging slice. The overall sensitivity and specificity of CTP for the detection of perfusion deficits in patients with proven territorial infarction (n = 18) on follow-up CT were 95% and 100%, respectively. The nAP 0 was significantly correlated with the National Institutes of Health Stroke Scale score at admission ( P F ( P 0 >HLA F ; n = 6), (2) initial perfusion deficit and nonnutritional reperfusion (nAP 0 ≥HLA F ; n = 2), and (3) initial perfusion deficit without reperfusion (nAP 0 ≥HLA F ; n = 2). Conclusions Computed tomographic perfusion imaging detects major perfusion deficits in the middle cerebral artery territory. Because CTP is broadly available, it may play a role in acute stroke management.

Abstract: The clinical value of magnetic resonance perfusion imaging (MRI) was investigated by quantitative comparison with 201thallium-single-photon emission computed tomography (201TI-SPECT) and quantitative coronary angiography (QCA). Short-axis imaging was performed during dipyridamole administration in 13 patients with single-vessel coronary artery disease. Using inner and outer contours, the myocardium was divided into 30 contiguous, radial regions. Defining a perfusion defect as a region with less than 90% of maximum 201TI intensity, nine patients had a matching perfusion defect, two had no defect on both 201TI-SPECT or MRI, and one had a defect on 201TI-SPECT but not on MRI. One patient had a defect on both modalities but with inaccurate localization. Three perfusion parameters were investigated: a) maximum contrast enhancement (MCE); b) slope of the signal intensity versus time curve; and c) inverse mean transit time (1/MTT). The sensitivity and specificity of MCE in the detection of perfusion abnormalities with TI-SPECT as the reference method were 71% and 71%, respectively (slope 77% and 61%, 1/MTT 44% and 70%). Furthermore, correlations were calculated per patient for the entire circumference of the short-axis myocardium. Median correlations were as follows: MCE 0.92, slope 0.91, and 1/MTT 0.40. Mismatches between 201TI defects and defects on MRI resulted in low mean correlations (MCE 0.45, slope 0.46, and 1/MTT 0.26). There was a trend between severity of perfusion defects on MRI (using MCE) and QCA stenosis area (r = −0.56, P = 0.06). Thus, MRI and 201TI-SPECT demonstrate fair agreement in the assessment of perfusion defects but show moderate correlation when the entire short-axis myocardium is correlated. J. Magn. Reson. Imaging 2000;11:607–615. © 2000 Wiley-Liss, Inc.

Abstract: Assessment of quantitative cerebral blood flow on a conventional fast CT machine without the use of specialized equipment may be valuable in the investigation of acute stroke and head injury. We aimed to compare a single slice CT perfusion sequence with H2150 positron emission tomography using the sagittal sinus as an input function, a method that avoids unnecessary orbital irradiation. Eight patients were studied, two patients with gliomas, and six with arteriovenous malformations. The dynamic CT perfusion sequence was performed by acquiring the same 7 0 mm slice 10 times over 30 sec during a 50 ml bolus of intravenous contrast medium given at a rate of 7.5 ml sec~^ using a power injector. The CT perfusion studies were completed without complication. Co-registration was sub-optimal in one patient. Overall the correlation between the two methodologies was encouraging with an average r2 value of0.524 for individual analyses. When two patients with high flow arteriovenous malformations were excluded...

Abstract: Magnetic resonance first-pass perfusion imaging has developed considerably over the past decade. It is possible to acquire 7-8 imaging planes every heartbeat at rest and in two heartbeats during stress using high-performance gradients and hybrid echoplanar methods. T1 weighting can be achieved with volumetric saturation pulses or selective "notch" pulses. First-pass studies can be quantified, but it also is possible to directly visualize myocardial perfusion abnormalities as subendocardial defects with less contrast enhancement than surrounding myocardium. It is feasible to detect stress-induced perfusion abnormalities in patients with coronary artery disease. Magnetic resonance imaging (MRI) perfusion abnormalities associated with myocardial infarction have significantly different characteristics from those seen on nuclear methods such as thallium, where the final appearance of images represents a combination of perfusion, viability, and wall thickness. Infarcted myocardium enhances during the first-pass MRI study unless there is microvascular or epicardial obstruction. Microvascular obstruction after myocardial infarction is easily detected and has adverse prognostic significance. Stress-induced perfusion abnormalities are not synonymous with coronary artery disease, as they can be detected in hypertrophic cardiomyopathy. MRI perfusion methods appear promising as long as physicians interpret the results in accordance of the physiology portrayed in the images.

Abstract: Magnetic resonance imaging (MRI) using laser-polarized noble gases, such as (129)Xe and (3)He, allows unparalleled noninvasive information on gas distribution in lung airways and distal spaces. In addition to pulmonary ventilation, lung perfusion assessment is crucial for proper diagnosis of pathological conditions, such as pulmonary embolism. Magnetic resonance perfusion imaging usually can be performed using techniques based on the detection of water protons in tissues. However, lung proton imaging is extremely difficult due to the low proton density and the magnetically inhomogeneous structure of the lung parenchyma. Here we show that laser-polarized (3)He can be used as a noninvasive probe to image, in a single MRI experiment, not only the ventilation but also the perfusion state of the lungs. Blood volume maps of the lungs were generated based on the (3)He signal depletion during the first pass of a superparamagnetic contrast agent bolus. The combined and simultaneous lung ventilation and perfusion assessments are demonstrated in normal rat lungs and are applied to an experimental animal model of pulmonary embolism. Magn Reson Med 44:1-4, 2000.

Abstract: Summary:The roles of noncontrast computed tomography (NCCT) and CT angiographic/CT perfusion (CTA/CTP) imaging in the rapid triage of clinically suspected hyperacute stroke patients to appropriate therapy is reviewed. Contraindications to thrombolysis include NCCT hemorrhage (absolute) and significa

Abstract: Perfusion imaging (PI) demonstrated increased perfusion and diffusion-weighted imaging (DWI) showed high signal limited to the left temporoparietal cortex in a 68-year-old man with nonconvulsive status epilepticus. The EEG showed a slow delta-wave focus. The patient recovered and PI, DWI and EEG changes completely resolved.

Abstract: There is growing evidence that the noninvasive assessment of myocardial perfusion with cardiovascular magnetic resonance is a valid and accurate tool for the assessment of ischemic heart disease and its introduction into routine clinical evaluation of patients is rapidly expected. Magnetic resonance measurements allow the evaluation of reversible and irreversible myocardial ischemia, the assessment of acute myocardial infarction, as well as the recognition and detection of viable myocardium. Magnetic resonance perfusion measurements are mainly performed with T1-shortening contrast agents such as gadolinium-DTPA either by visual analysis or based on the analyses of signal intensity time curves. For the detection of myocardial ischemia the first pass kinetics of a gadolinium-DTPA bolus and for the detection of myocardial necrosis and the definition of viable myocardium steady state distribution kinetics are assessed. Quantitative analysis of myocardial perfusion can be performed but requires complex modeling due to the characteristics of gadolinium-DTPA. Thus, semi-quantitative parameters are preferred. There is accumulating evidence in the literature that magnetic resonance imaging can be used for the detection of coronary artery stenosis with high diagnostic accuracy both with semi-quantitative or visual analysis. Myocardial infarction can be reliably detected and the infarcted area determined. Non-reperfused infarcted myocardium can be differentiated from reperfused myocardium by different enhancement patterns that correlates with viability. Cardiac magnetic resonance is a promising technique that can combine different functional studies during one examination, such as the assessment of wall motion and perfusion at rest and stress. With further improvements in analysis software magnetic resonance perfusion measurement may rapidly become a routine tool for the assessment of patients with coronary artery disease.

Abstract: This study was performed to examine the use of positron emission tomography (PET) as a method of evaluating myocardial perfusion after the arterial switch operation for correction of transposition of the great arteries. Eleven asymptomatic patients (median age 2.3 years, range 1.3-4.3 years) post successful neonatal arterial switch repair for transposition underwent cardiac PET scanning using N(13) ammonia before and after dipyridamole infusion. Reconstructed data from static scans were analyzed for regional perfusion defects before and after pharmacological stress. Simultaneous assessment of coronary flow before and after stress was performed using a Patlak graphical analysis of data from dynamic scans. Results obtained from PET scanning were correlated with patterns of coronary artery anatomy, electrocardiogram (ECG) recordings, and echocardiographic evaluation. PET scanning demonstrated normal distribution of myocardial perfusion before and after stress in all but one patient, who was found to have a discrete inferior transmural perfusion defect. The defect was well correlated with perioperative ECG changes and a complicated postoperative course. Myocardial blood flow before dipyridamole (0.690 ml/min/g) was similar to reported adult rest values. There was a small but significant (p < 0.002) increase in myocardial blood flow after dipyridamole stress with a mean coronary flow reserve of 1.19 (+/-0.103). Echocardiographic evaluation failed to demonstrate significant wall motion abnormalities in any of the patients. Cardiac PET scanning is a reliable noninvasive method for evaluation of myocardial perfusion in small children. In this study, the incidence of myocardial perfusion defects after the arterial switch operation is lower than previously reported. The data obtained concerning coronary flow and coronary flow reserve after the arterial switch need to be interpreted with caution because normal data in children are not available.

Abstract: Two magnetic resonance imaging techniques, diffusion and perfusion imaging, are being used increasingly for evaluation of pathophysiology of stroke. This article introduces these techniques and reports some initial studies using these approaches, together with conventional T2-weighted magnetic resonance imaging, for investigation of childhood stroke. It is shown that the combination of T2-weighted and diffusion images can provide information about the timing of stroke events in childhood, and perfusion imaging can detect abnormalities not visible by other magnetic resonance imaging techniques. These magnetic resonance methods therefore should play an important role in investigation of children with stroke and could be of particular value in studies of at-risk populations of children such as those with sickle cell disease.

Abstract: The STAR-HASTE sequence has been shown to be useful for perfusion imaging in areas that are plagued by magnetic susceptibility artifacts. Pulmonary perfusion imaging with this technique was attempted in this study. Quantitative analysis was also conducted, using an appropriate kinetic model in one subject. In six healthy subjects, gradual enhancement was observed in pulmonary artery to distal lung parenchyma when inflow time was increased. Our initial results suggest that noninvasive evaluation of pulmonary perfusion by magnetic resonance imaging without administration of an exogenous agent is possible.

Abstract: Myocardial Doppler velocity (MDV) imaging may provide an objective correlate of ischemia, thereby reducing the expertise needed for interpreting stress echocardiography and improving its reproducibility. This study sought to independently validate the results of exercise MDV imaging with single-photon emission computed tomography (SPECT) perfusion imaging in 116 patients (age 60+/-12 years, 28 women) referred for exercise SPECT for diagnostic or prognostic assessment of coronary artery disease. Two-dimensional echocardiography was performed with simultaneous color MDV data acquisition before and after exercise treadmill testing. MDV data were processed off-line to display myocardial velocity profiles in each segment at rest and peak exercise. SPECT was analyzed using a 16-segment model and segments were classified as normal or showing resting or stress defects. Resting defects within segments showing normal function were attributed to attenuation. Color MDV data were compared with SPECT results, and a multivariate analysis (including exercise and SPECT results) was performed to identify the determinants of the exercise MDV response. Patients exercised maximally (peak rate-pressure product 27.6+/-6.1x10(3), and SPECT was abnormal in 33 patients. Of the 1,333 left ventricular segments evaluable by SPECT and MDV, 1,217 segments were classified as normal, 43 showed a stress defect, and 73 a rest defect. Segmental comparison of thallium findings and MDV showed that segments with a rest defect had a lower velocity at rest and stress than normal segments (p<0.001). Segments with a stress defect had a marked reduction in peak exercise velocity and less increment in velocity than normal segments. Heart rate, functional capacity, and presence of abnormally perfused segments were independent predictors of myocardial velocity at peak exercise. Thus, color MDV correlates with independent evidence of ischemia, although it is also influenced by exercise capacity and left ventricular function. This technique may permit a feasible approach to quantitation of exercise echocardiography.