Abstract
Background: Perfusion Weighted Magnetic Resonance Imaging (PW-MRI) and HMPAO Single Photon Emission Computed Tomography (SPECT) are both cerebral perfusion measurement techniques. Imaging before and after acetazolamide administration can assess cerebrovascular reserve in symptomatic haemodynamic cerebrovascular disease. We compared SPECT and PW-MRI parameters in this patient group. Methods: We identified 10 patients with haemody-namically induced symptoms and intra- or extra-cranial arterial stenoses with back-to-back acetazolamide challenge SPECT and PW-MRI, 4 of whom had resting studies. Regions of interest (ROIs) were applied to parameter maps using an ASPECTS template and perfusion parameters expressed relative to contralateral ROIs, giving 118 challenge and 48 resting ROIs. Results: SPECT relative cerebral blood flow (rCBF) correlated with PW-MRI time to peak (TTP) (r = ?0.568), mean transit time (MTT) (r = ?0.317), regional cerebral blood flow (rCBF) (r = 0.299) and cerebral blood volume (CBV) (r = 0.224). Bias between SPECT and PW-MRI rCBF was small (?0.018) with wide limits of agreement and a systematic measurement error. Pre- to post-acetazolamide PW-MRI rCBF change showed poor sensitivity and specificity for detecting change in SPECT rCBF. SPECT and PW-MRI rCBF had stronger correlation and smaller bias in unilateral stenosis than with bilateral stenosis. Conclusion: Systematic bias between techniques limits interchange- ability in cerebrovascular reserve measurement in patients with cerebrovascular stenosis.
Highlights
Cerebral hypoperfusion may contribute to the pathogenesis of stroke or transient ischaemic attack in patients with occlusive cerebrovascular disease, recognised in the carotid system, where characteristic patterns of both clinical and radiological deficit are recognised [1]
Different brain perfusion imaging techniques have been used to assess cerebrovascular reserve (CVR). These include Single Photon Emission Computed Tomography (SPECT), which uses an intravenous radioactive tracer, most commonly Technetium 99-hexamethylpropylene amine oxime (99mTcHMPAO), which diffuses across the blood brain barrier and fixes in the brain tissue proportionately to flow, [8] and perfusion weighted Magnetic Resonance Imaging (PW-MRI), most commonly using intravascular gadolinium contrast bolus [9,10]
Perfusion Weighted Magnetic Resonance Imaging (PW-MRI) has the potential advantage that it does not expose patients to ionising radiation, and so could be more readily repeated, but has limitations that include exclusion of patients with metallic implants including cardiac pacemakers, or claustrophobia, and gadolinium contrast agents are contraindicated in patients with renal failure
Summary
Cerebral hypoperfusion may contribute to the pathogenesis of stroke or transient ischaemic attack in patients with occlusive cerebrovascular disease, recognised in the carotid system, where characteristic patterns of both clinical and radiological deficit are recognised [1]. Different brain perfusion imaging techniques have been used to assess CVR These include Single Photon Emission Computed Tomography (SPECT), which uses an intravenous radioactive tracer, most commonly Technetium 99-hexamethylpropylene amine oxime (99mTcHMPAO), which diffuses across the blood brain barrier and fixes in the brain tissue proportionately to flow, [8] and perfusion weighted Magnetic Resonance Imaging (PW-MRI), most commonly using intravascular gadolinium contrast bolus [9,10]. SPECT can be used to measure relative cerebral blood flow (CBF), whereas PW-MRI can produce various parameters including CBF, cerebral blood volume (CBV), signal time to peak (TTP), and mean transit time of the contrast bolus (MTT) [11]. Conclusion: Systematic bias between techniques limits interchangeability in cerebrovascular reserve measurement in patients with cerebrovascular stenosis
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