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The entire duration of 64-slice CTA, from start of contrast injection to conclusion of scanning, is approximately 20 to 25 sec. Because image acquisition only requires 3 to 4 sec, most of this time is due to the delay between when contrast is injected and when scanning is begun.
Intracranial vascular imaging: Pearls and pitfalls Jane J. Kim, MD, and Max Wintermark, MD T here has been increasing reliance diplopia, diffuse weakness and vomit- after the initial CTA, to reevaluate his on computed tomography angi- ing. Given the concern for posterior- vasculature (Figure 3). Again, there ography (CTA) and magnetic circulation ischemia, a CT/CTA was was no neurologic deterioration at the resonance angiography (MRA) for eval- requested and performed within the first time of the study. DSA demonstrated uation of the intracranial vasculature in hour of symptom onset (Figure 1). Our occlusion of the right vertebral artery, patients suspected of acute stroke. Digi- standard CT stroke protocol included occlusion of the left vertebral artery tal subtraction angiography (DSA), 64-slice CTA from the base of the heart proximal to the posterior inferior cere- while traditionally the gold standard, is through the cerebral vertex, as well as bellar artery (PICA), reconstitution of invasive and associated with potential delayed contrast-enhanced head CT the vertebrobasilar confluence distal to complications. Further, DSA is not read- obtained approximately 1 min after CTA the PICA, and occlusion of the remain- ily accessible anytime day or night. In (without the need for additional contrast der of the basilar artery with filling of the acute stroke setting, DSA is typically material because contrast has already the basilar tip via the posterior commu- reserved for patients undergoing thera- been injected for CTA). In this patient, nicating artery. peutic intervention with intra-arterial the initial CTA demonstrated lack of The important point about this case is thrombolysis or embolectomy. opacification of the bilateral distal verte- that CTA, contrast-enhanced CT, MRA The purpose of this article is to com- bral arteries and proximal basilar artery, and DSA obtained within 24 hours of pare the diagnostic accuracy of CTA, while the delayed contrast-enhanced each other, and without any change in MRA and DSA for evaluation of the images demonstrated normal opacifica- the patient’s clinical status, demon- intracranial circulation in patients with tion of the left distal vertebral artery and strated very different findings. Both stroke. We will discuss the technical proximal basilar artery. MRA and DSA appeared to demon- parameters and potential artifacts that Based on the clinical and imaging strate occlusion of the basilar artery, as must be understood so that an accurate findings, the patient received IV tissue well as occlusion of the bilateral distal interpretation of each modality can be plasminogen activator (tPA) and vertebral arteries. However, most of the made. We will structure our discussion underwent 3-dimensional time of flight basilar artery appeared patent on CTA, around an illustrative clinical case of a (TOF) intracranial MRA approxi- which showed occlusion limited to the patient who underwent CTA, MRA and mately 4 hours following CTA to bilateral distal vertebral arteries and DSA within a 24 hour time frame. reassess his vasculature after throm- only the most proximal aspect of the bolysis (Figure 2). The MRA demon- basilar artery. Delayed contrast- Clinical case strated absence of flow-related enhanced CT, in turn, appeared to A 62-year-old man presented to the enhancement in the bilateral distal ver- demonstrate patency of the distal left emergency room with acute onset tebral and entire basilar artery, which vertebral and entire basilar artery. was discrepant with the initial CTA, One explanation for the discrepancy Dr. Kim is Assistant Professor of Clini- especially considering that there was is that the patient’s basilar artery cal Radiology, Neuroradiology Section, San Francisco General Hospital, Uni- no change in the patient’s clinical thrombosed between the time of CTA versity of California, San Francisco, CA; examination and no evidence of neuro- and MRA/DSA. However, the absence and Dr. Wintermark is Chief of the Divi- logic deterioration between initial CTA of any neurological changes between sion of Neuroradiology, University of and follow-up MRA. examinations, as would be expected Virginia Health System, Charlottesville, The patient then underwent DSA the with a typically devastating basilar VA. following day, approximately 24 hours artery occlusion, weighs against this 28 ■ APPLIED RADIOLOGY © www.appliedradiology.com April 2010 INTRACRANIAL VASCULAR IMAGING A B
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