Tc-99m ECD neuro-SPECT and diffusion weighted MRI in the detection of the anatomical extent of subacute stroke: a cautionary note regarding reperfusion hyperemia

We present a case of subacute middle cerebral artery infarct, which demonstrates restricted diffusion on MRI and reperfusion hyperemia in the posterior half of the lesion on angiography. Tc-99m ethyl cysteinate dimer (ECD) SPECT obtained shortly after the MRI failed to demonstrate perfusion defects in the regions demonstrating reperfusion hyperemia on angiography, underestimating the true size of the infarct. Crossed cerebellar diaschisis is, however, present. SPECT studies obtained over the following weeks demonstrated gradual enlargement of the lesion to approximate the MRI signal changes over a 19-day period. The case presented demonstrates retention of ECD in the infarcted brain. Several studies have demonstrated that Tc-99m ECD uptake is dependent on preserved brain tissue function because tracer retention requires enzymatic esterase activity, rather than the passive, nonenergy dependent trapping of Tc-99m hexamethylpropyleneamine oxime. Hence, infarcted areas undergoing reperfusion hyperemia are unlikely to demonstrate ECD uptake. This report illustrates that MRI diffusion weighted imaging may be more accurate in demonstrating the full extent of reperfused infarcts earlier than Tc-99m ECD SPECT. SPECT in this case failed to demonstrate reduced uptake in reperfused regions of the infarct. Also, crossed cerebellar diaschisis may serve as an early marker of extensive neuronal dysfunction.     

Prognostic value of subacute crossed cerebellar diaschisis: single-photon emission CT study in patients with middle cerebral artery territory infarct

BACKGROUND AND PURPOSE: Although chronic-stage crossed cerebellar diaschisis (CCD) is reported to be associated with the neurologic state or clinical improvement after infarct, the prognostic value of early-stage CCD remains controversial. Our aim was to determine whether measurements of CCD in the acute and subacute stages obtained at single-photon emission CT (SPECT) facilitate the prediction of stroke outcome. METHODS: The pattern of cerebral blood flow changes after the occurrence of acute middle cerebral artery ischemia with severe cortical symptoms was examined by using technetium 99m-hexamethylpropyleneamine oxime ((99m)Tc-HMPAO) SPECT. Fifteen patients (mean age, 73 years +/- 8 [SD]) with unilateral ischemia were examined in the early subacute stage (10 days +/- 5). In 11 patients, SPECT was performed in both the acute (16 hours +/- 10) and subacute stages. From the total counts obtained from each cerebellar hemisphere, the asymmetry index (AI) was calculated as follows: [(value in unaffected hemisphere--value in affected hemisphere)/value in unaffected hemisphere] x 100. Clinical outcome (at 60 days) was assessed by means of the Scandinavian Stroke Scale (SSS) and Barthel Index (BI). RESULTS: AIs in the acute stage and clinical outcome (ie, SSS and BI scores) showed no significant correlation, but the severity of AI in the early subacute stage correlated significantly with both the final SSS (r = -0.69; P <.01) and BI scores (r = -0.82; P <.01). CONCLUSION: Cerebellar hypoperfusion detected at (99m)Tc-HMPAO SPECT in the early subacute stage in patients with supratentorial infarct indicates a worse clinical outcome.     

Dynamic and static 99mTc-ECD SPECT imaging of subacute cerebral infarction: comparison with 133Xe SPECT.

99mTc-ethylcysteinate dimer (99mTc-ECD) SPECT imaging reportedly fails to show reflow hyperemia in patients with subacute stroke. This study attempts to determine the clinical usefulness of dynamic 99mTc-ECD SPECT in evaluating regional blood flow in subacute cerebral infarction and the kinetic behavior of 99mTc-ECD in infarct areas. METHODS: 133Xe and consecutive dynamic and static 99mTc-ECD SPECT studies were performed on 24 patients with cortical infarction in the middle cerebral artery territory 13-15 d after the onset of a stroke. Image contrast between infarct and contralateral control areas on 99mTc-ECD tomograms (ECD uptake ratio) was compared with that on cerebral blood flow (CBF) images obtained using 133Xe inhalation (CBF ratio). RESULTS: In all cases, ECD uptake ratios from static images were lower than CBF ratios. This tendency was obvious when CBF in the infarct area increased above the normal control value, and no significant correlation was found between ECD uptake ratios from static images and CBF ratios. Only in the infarct areas with CBF below the normal control value, however, was a significant correlation between the two maintained (r = 0.795; P = 0.0011). A very strong correlation was found between CBF ratios and ECD uptake ratios on both the first dynamic scan (36 s after injection) (r = 0.991; P < 0.0001) and the second dynamic scan (72 s after injection) (r = 0.945; P < 0.0001). The correlation coefficient decreased in a time-dependent manner, with no significant correlation observed after the fourth dynamic scan (144 s after injection). On the other hand, significant correlations were observed on all dynamic scans only in the infarct areas with CBF below the control value. CONCLUSION: Super-early images of dynamic 99mTc-ECD SPECT provide a close imaging contrast with CBF and reveal reflow hyperemia in areas with irreversible changes produced by subacute stroke, which static 99mTc-ECD SPECT images fail to show. Decreased retention of the tracer in the infarct areas with hyperperfusion causes an underestimation of CBF on static 99mTc-ECD SPECT images. Given these results, we believe that dynamic 99mTc-ECD SPECT is an effective clinical tool to evaluate regional blood flow in subacute cerebral infarction.     

I-123 HIPDM planar brain images demonstrating crossed cerebellar diaschisis

I-123 HIPDM or IMP brain planar images, as well as SPECT images, have been useful in the detection of large lesion(s) of the cerebral cortex. Planar imaging may be useful not only for cerebral lesions, but also for a cerebellar abnormality and in certain clinical situations, such as phobia to a gantry or being too heavy for the imaging table, when SPECT imaging cannot be performed. The authors concur that a large cerebral lesion can be detected by planar images; in addition, cerebellar lesions, such as the presence of crossed cerebellar diaschisis (CCD), may be detectable by planar imaging using I-123 HIPDM. This article presents a patient with a large cerebral infarct detected by planar imaging whose CCD has been demonstrated by planar images.     

"Luxury perfusion" with 99mTc-HMPAO and 123I-IMP SPECT imaging during the subacute phase of stroke

To compare the merits of 123I-isopropyl-iodoamphetamine (123I-IMP) and 99mTc-HMPAO in showing abnormal brain uptake distribution during cerebral ischemia, we studied ten patients during the subacute phase of their stroke, a period where metabolism and blood flow are frequently uncoupled. SPECT imaging was performed using both radiopharmaceuticals in the 10 patients from 48 h to 4 weeks after onset of symptoms. Two patients out of the 10 had similar defects with 123I-IMP and 99mTc-HMPAO SPECT, the location of the defects corresponding to the area of infarction observed on CT. Six patients had normal 99mTc-HMPAO SPECT and abnormal 123I-IMP SPECT with defects in the area of infarction shown by CT. The remaining 2 patients had hyperactive abnormalities on 99mTc-HMPAO in areas corresponding to defects on the 123I-IMP images. Two of the patients with SPECT mismatches were studied again more than 1 month after onset. On reexamination, 99mTc-HMPAO SPECT which was previously normal or hyperactive became hypoactive with a focal area of decreased activity corresponding to the defect on 123I-IMP. Crossed cerebellar diaschisis was found in 7 patients with 99mTc-HMPAO and was absent for both 123I-IMP and 99mTc-HMPAO in 3. We suggest that SPECT with 99mTc-HMPAO could show transient hyperemia not demonstrated by 123I-IMP whereas in some cases cerebral infarction would be more difficult to demonstrate with 99mTc-HMPAO than with 123I-IMP. SPECT with both tracers is recommended to follow the evolution of strokes in terms of regional cerebral blood flow and tissue metabolism.     

F-18 FDG PET demonstrates crossed cerebellar diaschisis 20 years after stroke

Stroke produces an area of focal damage and distant areas of reduced blood blow and metabolism termed diaschisis. Tc-99m ECD and HMPAO brain SPECT have demonstrated crossed cerebellar diaschisis (CCD) in patients with cerebral cortical infarct. SPECT findings reflect abnormal cerebral blood flow. CCD as shown on F-18 FDG PET reflects abnormal reflects glucose metabolism. We present the case of a patient with laryngeal cancer who also had a stroke in the left cerebral hemisphere involving the territory of the middle cerebral artery 20 years ago. This patient underwent PET, including the head and neck. A current brain F-18 FDG PET exhibited hypometabolism in the contralateral cerebellum (CCD) as well as hypometabolism of the primary insult in the left cerebral hemisphere. These findings reflect partial impairment or diminished glucose metabolism in the primary insult to the cerebrum and contralateral cerebellum. In addition, this patient illustrates that on PET imaging, CCD could be demonstrated 20 years after a stroke.     

Early and delayed distribution of N-isopropyl-[I]-p-iodoamphetamine in haemorrhagic and ischaemic brain

Single photon emission computed tomography (SPECT) was used to study redistribution of N-isopropyl-[¹²³I]-p-iodoamphetamine (IAMP) in 10 patients with intracerebral haemorrhage and 7 with ischaemic stroke. Delayed/early IAMP uptake ratios (D/E) were calculated for four different cerebral zones: haematoma or infarct, perilesional, normal and crossed cerebellar diaschisis areas. Delayed uptake was observed in all areas, but there were no significant differences between the haematoma and infarct results nor between the lesional and perilesional results. Delayed redistribution of IAMP therefore did not seem to be associated with neuronal metabolic activity.     

Very early and standard Tc-99m ethyl cysteinate dimer SPECT imaging in a patient with reperfusion hyperemia after acute cerebral embolism.

It has been reported that Tc-99m ethyl cysteinate dimer (ECD) SPECT imaging may not show reperfusion hyperemia in patients with subacute stroke. The authors describe a patient with embolic middle cerebral artery occlusion who was examined using xenon-133 and dynamic and standard Tc-99m ECD SPECT immediately after early recanalization. Standard Tc-99m ECD SPECT images revealed hypoactivity in the ipsilateral middle cerebral artery territory. In contrast, the dynamic Tc-99m ECD SPECT images from the first scan (very early images acquired 36 seconds after injection) showed hyperactivity in the same region and provided imaging contrast comparable to what would be obtained with xenon-133 tomography. Hemorrhagic transformation later developed in this region. These results indicate that images from very early dynamic Tc-99m ECD SPECT of areas with irreversible changes produced by acute stroke can reveal reflow hyperemia that standard Tc-99m ECD SPECT images fail to show.     

“Luxury perfusion” with99mTc-HMPAO and123I-IMP SPECT imaging during the subacute phase of stroke

To compare the merits of¹²³I-isopropyl-iodoam-phetamine (¹²³I-IMP) and^99mTc-HMPAO in showing abnormal brain uptake distribution during cerebral ischemia, we studied ten patients during the subacute phase of their stroke, a period where metabolism and blood flow are frequently uncoupled. SPECT imaging was performed using both radiopharmaceuticals in the 10 patients from 48 h to 4 weeks after onset of symptoms. Two patients out of the 10 had similar defects with¹²³I-IMP and^99mTc-HMPAO SPECT, the location of the defects corresponding to the area of infarction observed on CT. Six patients had normal^99mTc-HMPAO SPECT and abnormal¹²³I-IMP SPECT with defects in the area of infarction shown by CT. The remaining 2 patients had hyperactive abnormalities on^99mTc-HMPAO in areas corresponding to defects on the¹²³I-IMP images. Two of the patients with SPECT mismatches were studied again more than 1 month after onset. On reexamination,^99mTc-HMPAO SPECT which was previously normal or hyperactive became hypoactive with a focal area of decreased activity corresponding to the defect on¹²³I-IMP. Crossed cerebellar diaschisis was found in 7 patients with^99mTc-HMPAO and was absent for both¹²³I-IMP and^99mTc-HMPAO in 3. We suggest that SPECT with⁹⁹mTc-HMPAO could show transient hyperemia not demonstrated by¹²³I-IMP whereas in some cases cerebral infarction would be more difficult to demonstrate with^99mTc-HMPAO than with¹²³I-IMP. SPECT with both tracers is recommended to follow the evolution of strokes in terms of regional cerebral blood flow and tissue metabolism.     

Prediction of improvement of left ventricular wall motion in patients with myocardial infarction--by using 99mTc-tetrofosmin and 123I-BMIPP myocardial SPECT at subacute phase

The relationship between myocardial perfusion, fatty acid metabolism, and cardiac functional recovery were investigated by using single photon emission computed tomography (SPECT) with 99mTc-1,2-bis[bis(2-ethoxyethyl)phosphino]ethane (tetrofosmin: TF) and lodine-123-beta-methyl-p-iodophenyl-pentadecanoic acid (BMIPP) in patients with myocardial infarction. We examined myocardial SPECT in 18 patients with acute myocardial infarction (AMI) underwent successful reperfusion therapy within 24 hours from onset. TF myocardial SPECT (early and delayed images) and BMIPP (early image) SPECT were performed 2 weeks after onset of AMI, and regional TF and BMIPP defect scores of the infarct area were scored visually by a 4-point system. There was a significant correlation between the defect score of the TF delayed image, BMIPP image and SD/chord (indicator of regional wall motion abnormalities on left ventriculograms) at subacute phase (TF: r = -0.592, p = 0.011, BMIPP: r = -0.643, p = 0.004). Good correlations were also found between the defect score of the TF delayed image, the BMIPP image and the SD/chord at chronic phase (TF: r = -0.491, p = 0.037, BMIPP: r = -0.599, p = 0.007). Furthermore, there was a significant correlation between the improvement of SD/chord (acute to chronic phase) and the degree of reverse redistribution score of TF (r = 0.735, p = 0.022), and discordance score between TF and BMIPP (r = 0.691, p = 0.037). In conclusion, resting BMIPP and TF myocardial SPECT performed in patients with subacute phase AMI were shown to be useful in predicting improvement of left ventricular function at chronic phase.     

Cerebellar vasoreactivity in stroke patients with crossed cerebellar diaschisis assessed by acetazolamide and 99mTc-HMPAO SPECT.

Crossed cerebellar diaschisis (CCD) tends to persist or even worsen after supratentorial infarction. Several studies have shown impairment of cerebral vasomotor responsiveness in the hemispheric area of diaschisis in patients with hemispheric infarction. This finding has led to the concern that the lack of CCD reversibility might be associated with chronic circulatory abnormalities. We therefore assessed the vasoreactivity in the cerebellar hemisphere in which diaschisis is manifested using acetazolamide (ACZ) and SPECT. METHODS: Eight stroke patients with CCD (5 with unilateral hemispheric infarcts and 3 with unilateral intracerebral hemorrhage) had 99mTc-HMPAO SPECT scanning at rest and 20 min after intravenous injection of 1.0 g ACZ. The time interval after stroke ranged from 25 to 904 d. From the total counts obtained from each cerebellar hemisphere, the asymmetry index (AI) was calculated as (unaffected - affected cerebellar hemisphere)/unaffected cerebellar hemisphere x100. RESULTS: After ACZ, the mean AI (8.7+/-6.6) was significantly decreased (P<0.05) compared with that at rest (17.7+/-5.8). Seven of the 8 patients showed decrease in the AI after ACZ. In 1 patient, the direction of the asymmetry was reversed after ACZ so that the AI was negative. The ACZ-induced change in the AI did not show a significant correlation with the time interval after stroke, whether calculated in absolute terms or as a percentage change. CONCLUSION: This study shows that normal vascular supply is maintained in the CCD-affected cerebellar hemisphere over long periods of time after a stroke. Thus, the lack of CCD reversibility may not be attributed to a chronic circulatory insufficiency. The results lend support to the concept of functional deactivation and subsequent transneuronal degeneration as a likely explanation for CCD. It is unclear whether decreased AI after ACZ indicates a higher vascular response of the affected cerebellar hemisphere than that of the normal side.     

Interictal crossed cerebellar hyperperfusion on Tc-99m ECD SPECT

Crossed cerebellar hyperperfusion (CCH) in epilepsy is a rare condition that is observed on ictal cerebral perfusion SPECT. The mechanism of CCH assumes that hyperperfusion in the epileptic foci of the unilateral supratentorium causes hyperperfusion secondary to the corticopontocerebellar pathway (CPCP)-mediated remote effect in the contralateral cerebellar hemisphere. This phenomenon is similar to that of crossed cerebellar diaschisis (CCD). In this report we demonstrated interictal CCH in a patient with epilepsy in technetium-99m-ethyl cysteinate dimer (Tc-99m ECD) SPECT of the brain. To the best of our knowledge, interictal CCH has not been reported in the literature. This is the first report to describe the phenomenon with interictal Tc-99m ECD SPECT.     

Comparison of dobutamine echocardiography and 99mTc-sestamibi tomography for prediction of left ventricular ejection fraction outcome after acute myocardial infarction treated with successful primary coronary angioplasty.

For patients with acute myocardial infarction who undergo primary percutaneous transluminal coronary angioplasty (PTCA), it is important to promptly identify those in whom a significant delayed improvement of global left ventricular function is to be expected as a result of successful treatment. METHODS: In 51 patients with acute myocardial infarction who underwent primary PTCA with a good angiographic result, the late outcome of the left ventricular ejection fraction (LVEF) was established after a 6-mo follow-up. In the early phase after infarction (within approximately 1 wk of infarction), the contractile reserve of the infarct zone was evaluated using dobutamine echocardiography and compared with the assessment of infarct size, infarct severity, and mean tracer activity of the infarct zone obtained using resting 99mTc-sestamibi SPECT. Receiver-operating-curve (ROC) analysis was used to define the reliability of the various parameters for identifying the patients with a follow-up LVEF increase of > or = 5 LVEF units. RESULTS: Of the 48 patients without restenosis at follow-up, 34 showed significant LVEF improvement. The evaluation of the contractile reserve of the infarct zone achieved an ROC curve area of 0.75 +/- 0.07 with 74% sensitivity, 71% specificity, and 73% overall accuracy. Of the 99mTc-sestamibi SPECT parameters, the extent of the infarct had no diagnostic value according to ROC analysis. The mean activity of the infarct zone had an ROC curve area of 0.64 +/- 0.09 with 82% sensitivity, 50% specificity, and 73% overall accuracy. The infarct severity had an ROC area of 0.76 +/- 0.08 (not significant vs. mean activity and vs. contractile reserve) with 77% sensitivity, 71% specificity, and 75% overall accuracy. CONCLUSION: Evaluation of the contractile reserve of the infarct zone using dobutamine echocardiography and assessment of the tracer activity of the infarct zone or infarct severity using 99mTc-sestamibi SPECT in the early phase after infarction are able to identify the patients in whom successful primary PTCA will be followed by significant late LVEF improvement.     

Nuclear medicine for general radiologists: clinical application of brain SPECT

Brain SPECT studies are used to evaluate the cerebral hemodynamic changes in cerebrovascular diseases and other neuro-psychiatric disorders. I-123 and Tc-99m labeled radiopharmaceuticals widely used for brain perfusion SPECT studies include I-123 IMP, Tc-99m HMPAO, and Tc-99m ECD. I-123 IMP is suitable for the quantitative evaluation of cerebral blood flow, while Tc-99m HMPAO and Tc-99m ECD have problems owing to the non-linearity between cerebral radioactivity and cerebral blood flow. In addition, Tc-99m ECD does not show cerebral blood flow in the subacute phase of cerebral infarct or other conditions. Thus, it is important to consider the characteristics of radiopharmaceuticals and the clinical aspect of brain lesions in the interpretation of brain perfusion SPECT images. In this review, some useful information on brain perfusion SPECT is presented mainly as it relates to the cerebrovascular diseases.     

Visualization of pressure-dependent luxury perfusion in a patient with subacute cerebral infarction

Luxury perfusion characterized by depressed metabolism compared with CBF might be changed by decreasing cerebral perfusion pressure during the sitting position. A 77-yr-old man with subacute cerebral infarction was studied with brain X-ray computed tomography (CT), raise-up test with^99mTc-d,1-hexamethylpropyleneamine oxime (HMPAO) brain single photon emission tomography (SPECT) and positron emission tomography (PET). Brain X-ray CT revealed a low-density area in the left middle cerebral artery (MCA) anterior area. Raise-up^99mTc-HMPAO brain SPECT revealed decreased uptake in the left MCA anterior area in the sitting position and subsequent supine^99mTc-HMPAO brain SPECT revealed hot accumulation there. PET study in the supine position demonstrated some differences between CBF and the cerebral metabolic rate for oxygen in the left MCA anterior area, indicating luxury perfusion. CBF in the area of luxury perfusion might be decreased during the sitting or standing position and increased during the supine position by dysautoregulation of the cerebral vessels in the luxury perfusion during the subacute infarct.     

Remote effects in cerebral infarction--123I-IMP SPECT study

We studied the remote effects in 29 patients with middle cerebral artery territory infarction by using single photon emission computed tomography (SPECT) with N-isopropyl-p-[123I]iodoamphetamine. SPECT demonstrated a reduction in blood flow in the cerebellar hemisphere contralateral to the cerebral infarct, the cortex ipsilateral to the subcortical infarct, the visual cortex distal to the optic radiation lesion, and the thalamus ipsilateral to the cortical infarct. In addition to transient neuronal depression identified with diaschisis, our results indicated that persistent phenomena were apparently involved in these remote effects. The degenerative processes might be related to irreversible effects in remote areas. Clinical symptoms corresponding to the areas of hypoperfusion remote from infarcted lesions were not necessarily present.     

Hemodynamic and metabolic state of hyperfixation with99mTc-HMPAO brain SPECT in subacute stroke

By means of positron emission tomography (PET), we investigated the hemodynamic and metabolic state of the hyperfixation identified as the increased accumulation with 99mTc-d,l-hexamethylpropyleneamine oxime (HMPAO) by single photon emission computed tomography (SPECT) in patients with subacute stroke. We studied four patients with subacute stroke having hyperfixed areas evaluated with CBF, CMRO2, OEF and CBV by PET. The hyperfixation rate with 99mTc-HMPAO was obtained by comparing the surplus rate with standardized CBF. The OEF and CMRO2 values in the hyperfixed areas of 4 patients were significantly lower than those in normal 5 controls (p < 0.01), but CBF and CBV were almost the same in patients and normal controls, but the hyperfixation rate of 0.30 +/- 0.15 in 4 patients correlated well with CBV (r = 0.97, y = 11.75x + 0.42; p < 0.05). Hyperfixation with 99mTc-HMPAO in the infarct area revealing a mismatch between CMRO2 and CBF meant relative luxury perfusion. The hyperfixation rate determined by 99mTc-HMPAO brain SPECT correlated with CBV in the PET study. We can conclude that one of the main factors which caused hyperfixation was vasodilatation as well as the blood brain barrier disruption and the neovascularization.     

SPECT脑血流灌注显像在老年人脑梗塞中的应用

目的：评价ＳＰＥＣＴ脑血流灌注显像在老年病中的临床应用价值。材料和方法：４６例脑梗塞患者行９９ｍＴｃ－ＥＣＤ脑血流灌注显像，并与ＣＴ、ＭＲＩ、对照。其中４例行Ｄｉａｍｏｘ脑血流负荷检查。结果：４６例脑梗塞患者４５例脑血流灌注异常，占９７．８％．３３例同时做过ＣＴ，其灵敏度９６．７％．２５例做过ＭＲＩ，灵敏度９６％。ＳＰＥＣＴ脑血流显像灵敏度与ＣＴ及与ＭＲＩ间无显著性差异（Ｐ＞０．０５）。７例ＳＰＥＣＴ图像上出现＂交叉性小脑神经失联络征＂。４例行Ｄｉａｍｏｘ脑血流负荷检查，１例原梗塞灶血流明显改善；两例显示病灶范围更广泛；另１例除小脑血流分布改善外．余处未见明显改变。４例中３例有＂交叉性小脑神经失联络征＂，使用Ｄｉａｍｏｘ后小脑血流改善。结论：本组病例ＳＰＥＣＴ灵敏度与ＣＴ及ＭＲＩ无显著差异；ＳＰＥＣＴ脑血流灌注显像可探测梗塞后存活的脑组织，为临床治疗提供客观依据；结合Ｄｉａｍｏｘ脑血流负荷检查有望进一步提高诊断的阳性率     

Prediction of improvement of cerebral perfusion with I-123 iomazenil SPECT

We report a case of 61-year old man who was suffering from cerebrovascular disease with right hemiparesis and received I-123 iomazenil (IMZ) SPECT prior to carotid endoarterectomy. Severe stenosis of the right internal carotid artery and occlusion of the left middle cerebral artery (MCA) were revealed by cerebral angiography, and a hypoperfused area in left MCA territory and crossed cerebellar diaschisis (CCD) on I-123 IMP SPECT was demonstrated. In contrast, IMZ SPECT showed symmetric normal distribution. After the carotid endoarterectomy, the hypoperfused area in left MCA territory on IMP SPECT and hemiparesis had improved. It is thought that IMZ SPECT can be a useful tool for the prediction of improvement of cerebral perfusion and the clinical outcome.     

Hypofixation and hyperfixation of 99mTc-hexamethyl propyleneamine oxime in subacute cerebral infarction.

The relationship between hypofixation and hyperfixation of 99mTc-hexamethyl propyleneamine oxime (99mTc-HMPAO) remains unclear. The purpose of this study was to compare 99mTc-HMPAO SPECT with regional cerebral blood flow (CBF) imaging using 133Xe inhalation in patients with subacute cerebral infarction and to investigate the behavior of 99mTc-HMPAO in the infarct area using dynamic SPECT. METHODS: 133Xe and consecutive 99mTC-HMPAO SPECT studies, the latter of which consisted of dynamic and static scanning, were performed on 51 patients (22 women, 29 men; age range, 40-83 y; mean age, 61 y) with cortical infarction in the middle cerebral artery territory 13-15 d after stroke onset. One region of interest (ROI) was drawn in the infarct area. The control ROI was mirrored to the contralateral side, and the same set of ROIs was applied to all SPECT studies. Fractional fixation of 99mTc-HMPAO in the infarct area was evaluated relatively as the ratio of the infarct-to-control region in 99mTc-HMPAO static tomograms/the ratio of the infarct-to-control region in CBF images using 133Xe inhalation and was classified as hyperfixation when this value was >1.1 and hypofixation when this value was <0.9. To investigate the behavior of 99mTc-HMPAO in the infarct area, the second (36-72 s after tracer injection) and eighth (252-288 s after tracer injection) of 8 dynamic scans were selected, and the washout rate was calculated using the formula: 1 - (mean count in the eighth scan/mean count in the second scan). RESULTS: The infarct area showed hyperfixation of 99mTc-HMPAO when CBF in the area was 35 mL/100 g/min or less and showed hypofixation when CBF was >45 mL/U100 g/min. The washout rate was usually negative when CBF imaging using 133Xe inhalation was <20 mL/100 g/min but was positive when it was >45 mUL/100 g/min. The washout rate was negative when the infarct area showed hyperfixation of 99mTc-HMPAO but was positive when it showed hypofixation. CONCLUSION: 99mTc-HMPAO SPECT underestimates CBF in high-flow regions and overestimates CBF in low-flow regions of subacute cerebral infarction. 99mTc-HMPAO hypofixation and hyperfixation are associated with backdiffusion from the brain to blood and gradual accumulation of hydrophilic metabolites, respectively. Dynamic images should be useful for discriminating between 99mTc-HMPAO hypofixation and hyperfixation.