Joint Program in Nuclear Medicine

Diamox Imaging of the Brain

Barry Julius, MD
Scott Britz-Cunningham, MD

February 3, 2004

Presentation

A 49-year-old male presented with transient ischemic attacks (TIAs).

Imaging Technique

Thirty mCi of Tc-99m ECD was administered intravenously. SPECT imaging of the brain was performed both at baseline and after administration of 1000 mg intravenously.

Imaging Findings

SPECT imaging of the brain reveals moderately decreased radiopharmaceutical uptake at the left parietal, temporal and posterior frontal lobes after administration of diamox (shown with arrows). Baseline imaging demonstrates symmetric normal bilateral radiopharmaceutical uptake at the brain.

CT scan demonstrates a left dense middle cerebral artery (shown with arrow). Gray white matter differentiation is still maintained.

CT angiography demonstrates absence of contrast enhancement at the left middle cerebral arterial (MCA) distribution and decreased left cerebral hemispheric arterial collateralization compared to the right cerebral hemisphere. The intensity of the vessels on the left is decreased as compared with those on the right.

Post extracranial-intracranial artery (ECA ICA) bypass, CT angiography demonstrates persistently decreased left MCA arterial enhancement and decreased left cerebral collateralization. Again note the decrease in the vessels on the left.

Diagnosis

Ischemia in the left middle cerebral artery distribution caused by middle cerebral arterial thrombosis.

Discussion

Introduction

There are multiple causes of ischemia including thrombosis, aneurysms, tumors, arterial venous malformations. Arterial thrombosis can be a cause for infarction, cerebral emboli and may need to be treated. Acetazolamide perfusion imaging is a mechanism for determining the vascular reserve of the hemispheric abnormality for possible revascularization.

Imaging Modalities

The primary imaging modalities at the present time includes CT scan, CT angiography, MRI, MR angiography, and acetazolamide SPECT perfusion imaging.
CT scan is appropriate for determining any acute findings that may be associated with thrombosis such as hemorrhage or acute infarction.
MRI is appropriate for determining any acute findings that may be associated with thrombosis such as dating of hemorrhage, acute infarction, and other causes for thrombosis such as tumors and arteriovenous malformations.
CT and MR angiography is an appropriate anatomic modality for determination of the anatomy of the circle of Willis including arterial occlusions and narrowing. Collateralization can also be assessed prior to other imaging.
Acetazolamide perfusion imaging presently plays a role in determining if the region of vascular thrombosis may be clinically significant and if there is a role for intervention.

Acetazolamide Action Mechanism

Acetazolamide is a carbonic anhydrase inhibitor that acts as cerebral vasodilator. Ischemic tissue will demonstrate decreased uptake of cerebral perfusion radiopharmaceutical because of decreased vascular reserve relative the normal spared brain parenchyma. Acetazolamide peaks in the blood stream at 20 minutes.

Common Reasons for Cerebral Perfusion Acetazolamide Imaging

Acetazolamide cerebral perfusion imaging is most commonly used as a test for vascular reserve in such entities as stroke, transient ischemic attacks, arteriovenous malformations, epilepsy, and dementia prior to intervention. One series of 44 patients noted that patients with increased collateralization and positive reactivity to diamox imaging demonstrated improved flow upon intracranial bypass surgery.

Future Directions for Cerebral Perfusion Acetazolamide Imaging

There are many potential applications for imaging with acetazolamide. Multiple preliminary studies have been performed some of which include differentiation of vascular dementias from Alzheimer's disease, diagnosis of autoimmune syndromes, prediction of hyperperfusion syndrome post intervention, detection of hypoperfusion prior to coiling or balloon occlusion, diagnosis of migraines, and prognosis determination for stroke victims.

References

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J. Anthony Parker, MD PhD, Tony_Parker@CareGroup.Harvard.edu