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Published on: December 28, 2014
Hypofixation and hyperfixation of 99mTc-hexamethyl propyleneamine oxime in subacute cerebral infarction
K Ogasawara1, A Ogawa, K Koshu
1Department of Neurosurgery and Cyclotron Research Center, Iwate Medical University, Morioka, Japan.
Unlabelled:
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.
Insights
99mTc-HMPAO SPECT imaging in subacute cerebral infarction shows that hypofixation indicates higher cerebral blood flow (CBF) and hyperfixation indicates lower CBF. Dynamic SPECT imaging helps differentiate between these 99mTc-HMPAO fixation patterns.
Area of Science:
- Neurology
- Nuclear Medicine
- Radiopharmacology
Background:
- The diagnostic utility of 99mTc-hexamethyl propyleneamine oxime (99mTc-HMPAO) SPECT in subacute cerebral infarction is limited by unclear hypofixation and hyperfixation patterns.
- Regional cerebral blood flow (CBF) assessment is crucial for understanding infarct pathophysiology.
Purpose of the Study:
- To compare 99mTc-HMPAO SPECT findings with 133Xe inhalation CBF imaging in patients with subacute cerebral infarction.
- To investigate the behavior of 99mTc-HMPAO in infarct areas using dynamic SPECT.
Main Methods:
- 51 patients with middle cerebral artery territory infarction underwent 133Xe inhalation CBF imaging and consecutive 99mTc-HMPAO SPECT (dynamic and static).
- Regions of interest (ROIs) were placed in infarct and contralateral areas.
- Fractional fixation was calculated as the ratio of infarct-to-control 99mTc-HMPAO uptake to infarct-to-control CBF.
- Washout rate was calculated from dynamic SPECT scans to assess tracer behavior.
Main Results:
- 99mTc-HMPAO hyperfixation was observed when CBF was ≤35 mL/100 g/min, while hypofixation occurred when CBF was >45 mL/100 g/min.
- Washout rates were typically negative with low CBF (<20 mL/100 g/min) and positive with high CBF (>45 mL/100 g/min).
- Negative washout rates correlated with 99mTc-HMPAO hyperfixation, and positive rates with hypofixation.
Conclusions:
- 99mTc-HMPAO SPECT can underestimate CBF in high-flow regions and overestimate it in low-flow regions of subacute cerebral infarction.
- Hypofixation is linked to backdiffusion from brain to blood, while hyperfixation suggests gradual accumulation of hydrophilic metabolites.
- Dynamic SPECT imaging is valuable for distinguishing between 99mTc-HMPAO hypofixation and hyperfixation.
