Cerebellar vascular response to acetazolamide in crossed cerebellar diaschisis: a comparison of 99mTc-HMPAO single-photon emission tomography with 15O-H2O positron emission tomography

Neuro-SPECT: On the development and function of brain emission tomography in the Copenhagen area

This review describes the development of single-photon emission tomography (SPECT) in the Copenhagen area under the leadership of the internationally renown scientist, Niels A. Lassen, and the history leading up to construction of the tomograph. Measurements of global cerebral blood flow (CBF) in the 1940s and 1950s were performed by Kety & Schmidt and Lassen & Munck. Determination of regional cerebral blood flow (rCBF) by intra-arterial injection of ¹³³ Xe and measurement with a 254-multicrystal scintillation detector and a computer system was a major step forward in the study of physiology and pathophysiology of cortical cerebral blood flow. Tomography with radioisotope ligands, including non-invasive administration, was advanced in different centres during the 1970s. An emission tomograph, the Tomomatic 64, was developed as a result of a multidisciplinary Danish and international collaboration. It was the first emission tomograph to provide dynamic data that could produce cross-sectional rCBF images. The present description of the construction and function of the Tomomatic 64 includes comparison with other contemporary and later brain-dedicated SPECT systems. Basic and clinical application of the Tomomatic 64 in Copenhagen resulted in several hundred important scientific publications and improved diagnostics for patients with a variety of neurological disorders. It is concluded that the development of the Tomomatic 64 was a major step forward in the study and examination of rCBF and brain function related to several brain disorders, in addition to vascular diseases.

Brain Perfusion Imaging Under Acetazolamide Challenge for Detection of Impaired Cerebrovascular Reserve Capacity: Positive Findings with 15O-Water PET in Patients with Negative 99mTc-HMPAO SPECT Findings

Cerebrovascular reserve capacity (CVRC) is an important parameter for treatment decisions in chronic cerebrovascular diseases. It can be assessed by measuring the acetazolamide-induced change in regional cerebral blood flow using SPECT with ^99mTc-labeled hexamethylpropyleneamine oxime (^99mTc-HMPAO) or PET with ¹⁵O-water. Methods: Our database was searched for patients with moyamoya vasculopathy or atherosclerotic cerebrovascular disease who had undergone ¹⁵O-water PET after normal ^99mTc-HMPAO SPECT results with respect to CVRC. ¹⁵O-water PET was analyzed visually and quantitatively. Quantitative analysis was based on parametric CVRC maps generated by voxelwise image subtraction. Results: The search identified 18 patients (43 ± 15 y, 12 moyamoya vasculopathy). PET revealed impaired CVRC in 8 patients (44%). Quantitative analysis confirmed the positive visual findings in ¹⁵O-water PET and the negative findings in ^99mTc-HMPAO SPECT. Conclusion:¹⁵O-water PET enables detection of impaired CVRC in a considerable fraction of symptomatic patients with stenoocclusion and negative ^99mTc-HMPAO SPECT.

The cerebral vasomotor response in varying CO(2) concentrations, as evaluated using cine phase contrast MRI: Flow, volume, and cerebrovascular resistance indices

PURPOSE

Previous studies have identified that impaired cerebral vasomotor reactivity (VMR) is associated with a higher risk of stroke and transient ischemic attack. This study aims to evaluate VMR by measuring the blood flow waveforms of the supplying arteries and dural sinuses using cine phase contrast MRI (PC MRI) and hypercapnic challenge.

METHODS

PC MRI flow quantification was performed on an oblique slice approximately perpendicular to the target vessels to include the left (LICA) and right internal carotid artery (RICA), basilar artery (BA), sinus rectus (SR), and superior sagittal sinus (SSS). A total of four PC MRI scans were performed at different CO(2) concentrations (room air and 3%, 5%, and 7% CO(2)).

RESULTS

The analyses obtained the flow parameters and cerebrovascular resistance parameters for all five vessels. Results indicated that the vascular resistance indices decreased with increasing CO(2) concentration in four vessels (LICA, RICA, BA, and SR). The obtained VMR parameters demonstrated exponential increases with increasing CO(2) concentration.

CONCLUSIONS

Using entire blood flow waveforms, this study applied separate flow dynamics during systolic and diastolic periods to obtain cerebrovascular resistance parameters and extensive flow-related information. It is the first to investigate the cerebrovascular resistance parameters under hypercapnic challenge using cine MRI. This technique could provide a useful tool for clinical application in cerebrovascular disease.

Imaging of perfusion, angiogenesis, and tissue elasticity after stroke

Blood flow interruption in a cerebral artery causes brain ischemia and induces dramatic changes of perfusion and metabolism in the corresponding territory. We performed in parallel positron emission tomography (PET) with [(15)O]H(2)O, single photon emission computed tomography (SPECT) with [(99m)Tc]hexamethylpropylene-amino-oxime ([(99m)Tc]HMPAO) and ultrasonic ultrafast shear wave imaging (SWI) during, immediately after, and 1, 2, 4, and 7 days after middle cerebral artery occlusion (MCAO) in rats. Positron emission tomography and SPECT showed initial hypoperfusion followed by recovery at immediate reperfusion, hypoperfusion at day 1, and hyperperfusion at days 4 to 7. Hyperperfusion interested the whole brain, including nonischemic areas. Immunohistochemical analysis indicated active angiogenesis at days 2 to 7, strongly suggestive that hyperperfusion was supported by an increase in microvessel density in both brain hemispheres after ischemia. The SWI detected elastic changes of cerebral tissue in the ischemic area as early as day 1 after MCAO appearing as a softening of cerebral tissue whose local internal elasticity decreased continuously from day 1 to 7. Taken together, these results suggest that hyperperfusion after cerebral ischemia is due to formation of neovessels, and indicate that brain softening is an early and continuous process. The SWI is a promising novel imaging method for monitoring the evolution of cerebral ischemia over time in animals.

Diagnostic performance of Tc-99m HMPAO SPECT for early and late onset Alzheimer's disease: a clinical evaluation of linearization correction

OBJECTIVE

This study examined the influence of linearization correction (LC) on brain perfusion single-photon emission computed tomography (SPECT) for the diagnosis of Alzheimer's disease (AD).

METHODS

The early onset group (<65 years old) consisted of 10 patients with AD, and the late onset group (>/=65 years old) of 13 patients with AD. Age-matched controls included seven younger and seven older normal volunteers. Tc-99m hexamethyl propyleneamine oxine (HMPAO) SPECT images were reconstructed with or without LC [LC (+) or LC (-)] and a statistical analysis was performed using a three-dimensional stereotactic surface projection (3D-SSP). In addition, a fully automatic diagnostic system was developed, which calculated the proportion of the number of abnormal pixels in the superior and inferior parietal lobule, as well as in the precuneus and posterior cingulate gyrus.

RESULTS

The areas under the receiver-operating characteristic curve (AUCs) of the early onset group for conventional axial SPECT images, SPECT + 3D-SSP images and the fully automatic diagnostic system were 0.71, 0.88, and 0.92 in LC (-) and 0.67, 0.85, and 0.91 in LC (+), respectively. The AUCs of the late onset group were 0.50, 0.61, and 0.79 in LC (-) and 0.49, 0.67, and 0.85 in LC (+), respectively.

CONCLUSION

LC on Tc-99m HMPAO SPECT did not significantly influence the diagnostic performance for differentiating between AD and normal controls in either early or late onset AD. Further examination with individuals suffering from very mild dementia is, therefore, expected to elucidate the effect of LC on minimally hypoperfused areas.

Effects of aging on the cerebral distribution of technetium-99m hexamethylpropylene amine oxime in healthy humans

Some brain functions decline at a linear rate throughout adulthood. Others remain relatively stable until very late in the life cycle. This study characterized the effects of aging on the regional cerebral distribution of hexamethylpropylene amine oxime (HMPAO) in healthy human volunteers. The sample consisted of 26 men and 18 women with a mean age of 41.6+/-14.9 years (range: 19-73). Their past medical histories, physical examinations, and laboratory screening tests were normal. Single-photon emission tomography (SPET) scans of the brain were performed with a standardized acquisition and processing protocol on a triple-headed camera equipped with fan beam collimators. A 3-D restorative filter and a correction for uniform attenuation were applied before the images were reinterpolated in planes parallel to the line connecting the frontal and occipital poles. Mean counts per pixel were measured in multiple regions of interest (ROIs) within each hemisphere by custom fitting a set of templates to the images. The mean activity in each ROI was compared with the mean activity per pixel in the whole brain. Regression analyses were used to relate the activity ratios to age with both linear and nonlinear models. The relative concentration of radioactivity decreased significantly with age in most, but not all, gray matter structures. It increased in the white matter regions. The nonlinear model of aging fit the data significantly better than a straight line did. Most of the changes with age occurred during young adulthood. No further changes were detectable after the onset of middle age. The median breakpoint age at which the rate of change became negligible was 36.6 years. Aging significantly affects the relative uptake of HMPAO in healthy humans. It decreases in many gray matter regions and increases in most white matter regions. However, the changes do not appear to be linear. Most seem to occur during young adulthood before people reach their late thirties. The distribution then appears to remain relatively stable throughout middle age.