A total of nine normal volunteer subjects were studied with three forms of [99mTc] hexamethylpropyleneamineoxime (HM-PAO), a potential cerebral blood flow imaging agent. One, the d,l isomer, showed 4.1% uptake in the brain which remained constant over 8 hr. There was good differentiation between uptake in gray and white matter on tomographic slices. We propose that this agent may allow regional cerebral blood flow imaging to be performed on a routine basis.

https://jnm.snmjournals.org/content/27/2/171.full.pdf

Technetium-99m HM-PAO stereoisomers as potential agents for imaging regional cerebral blood flow: human volunteer studies.

Forty-six patients were studied with N-isopropyl I-123 p-iodoamphetamine (IMP) and the Harvard Scanning Multidetector Brain System. In nine control patients, good differentiation between the gray and white matter of the cerebral cortex and the basal ganglia was evident. Regional uptake was affected by physiologic maneuvers (visual stimulation). In 24 patients studied for stroke, IMP images demonstrated areas that were involved in acute infarction in eight patients whose initial transmission computerized tomography (TCT) was normal; IMP also showed perfusion abnormalities larger than the TCT abnormality in ten patients. Perfusion abnormalities were present in 23/24 of these patients. Seven patients studied with a history of TIA had normal TCT and IMP images. In three patients studied during seizure activity, regions of hyperperfusion corresponded to the EEG seizure focus. Markedly decreased activity was present in three patients with brain tumor and corresponded to the focal abnormality on the TCT study. Our study demonstrates the feasibility of assessing regional brain perfusion using a radiopharmaceutical that is lipid soluble and has a high extraction fraction in the brain, together with single-photon ECT.

https://jnm.snmjournals.org/content/23/3/191.full.pdf

Initial experience with SPECT (single-photon computerized tomography) of the brain using N-isopropyl I-123 p-iodoamphetamine: concise communication

The metabolic degradation and the kinetics of the cerebral uptake of N, N, N'-trimethyl-N'-(2-hydroxy-3-methyl- 5-[125I]iodobenzyl)-1, 3-propanediamine ([125I]HIPDM) have been studied in conscious, adult male Sprague-Dawley rats to determine its suitability as a tracer for the quantitative measurement of regional CBF (rCBF). rCBF was calculated by the indicator fractionation and the tissue equilibration methods in experiments of different durations up to 1 h. The values of rCBF obtained with [125I]HIPDM were compared with those obtained in concurrent measurements with [14C]iodoantipyrine in the same animals. Results of the experiments demonstrate that [125I]HIPDM is an inadequate tracer for use with the indicator fractionation method and that any method that employs [125I]HIPDM for the determination of rCBF must take into account its metabolic degradation, diffusion limitations, and bidirectional flux across the blood-brain barrier. With the tissue equilibration method, consistent determinations of rCBF m...

https://journals.sagepub.com/doi/pdf/10.1038/jcbfm.1985.12

Metabolic and kinetic considerations in the use of [125I]HIPDM for quantitative measurement of regional cerebral blood flow.

The rCBF was evaluated using I-123 HIPDM and single photon emission computed tomography (SPECT) on 14 patients undergoing extracranial-intracranial (EC-IC) bypass surgery because of internal carotid artery (ICA) occlusion. Before surgery, all patients showed cortical areas of hypoperfusion over the affected cerebral hemisphere. Shortly after EC-IC bypass a rCBF increase was observed in six patients. However, at the 6 and 12 month follow-ups, with angiographic control of bypass patency, rCBF studies did not show any significant rCBF change. Long-term noninvasive tomographic monitoring of perfusion changes occurring after EC-IC bypass surgery failed to show a long-lasting improvement in perfusion.

https://jnnp.bmj.com/content/jnnp/50/8/988.full.pdf

Long-term noninvasive single photon emission computed tomography monitoring of perfusional changes after EC-IC bypass surgery.

Generators for short-lived gamma and positron emitting radionuclides: current status and prospects.

Continuous carotid infusion of short-lived krypton-81m (t1/2 13 sec) yields an assessment of regional cerebral perfusion. This assessment can be obtained in three dimensions if activity is recorded with a rotating gamma camera and a computer to reconstruct krypton-81m distribution in tomographic sections. These showed several advantages over conventional views: (a) visualization of blood-flow distribution within brain structures (gray and white matter, basal ganglia); (b) more accurate location and evaluation of areas of relatively reduced or increased perfusion; (c) better definition of patterns of collateral circulation; (d) greater sensitivity and specificity in detecting and defining blood-flow changes during physiological activation studies. A limitation of the krypton-81m technique is its invasiveness. However, this study shows that the combination of new advances in radiochemistry with single-photon emission computed tomography may result in accessible methods for assessing, noninvasively and in three dimensions, the behavior of cerebral function in man.

https://jnm.snmjournals.org/content/21/12/1139.full.pdf

Tomographic assessment of cerebral perfusion using a single-photon emitter (krypton-81m) and a rotating gamma camera.

Functional images of brain perfusion can be obtained by a steady-state method which exploits the peculiar physical characteristics of the radioactive gas 81mKr.2 This is a very short half-lived isotope (13 sec half-life), which can be continuously produced either in the gaseous or the solution phase from its parent 81Rb (4.6 hours half-life). It emits 190 keV γ rays, an ideal energy for recording with an Anger γ camera. Because of its short half-life, continuous carotid infusion of 81mKr in solution will never eventually result in the equilibrium of this diffusible tracer within the brain; during continuous infusion continuous recording of the activity over the brain will therefore reflect at any time regional arrival of tracer, which is a linear function of regional perfusion. Thus, when used in conjunction with an ordinary Anger γ camera, it provides images of cerebral perfusion in two dimensions.

Regional Cerebral Perfusion Assessed with 81mKr and Emission Computerized Tomography

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Tomographic assessment of cerebral perfusion using a single-photon emitter (krypton-81m) and a rotating gamma camera.

Regional Cerebral Perfusion Assessed with 81mKr and Emission Computerized Tomography