Stefan Margiewicz M.D. Anant Krishnan M.D. Lindsey Kirk M.D. Chris Kazmierczak M.D.

1. eP – 23 – Optimizing MRA Evaluation of Supraclinoid Aneurysms. A Comparison in Detecting Supraclinoid Aneurysms Using Whole 3D MRA MIPs Versus Half 3D MRA MIPs Stefan Margiewicz M.D. Anant Krishnan M.D. Lindsey Kirk M.D. Chris Kazmierczak M.D. Department of Radiology, Oakland University William Beaumont School of Medicine and Beaumont Hospital - Royal Oak

2. Financial Disclosures • The authors do not have any financial disclosures.

4. Purpose • Intracerebral aneurysms are localized weaknesses in the blood vessels that cause focal dilations or areas of ballooning. • Small aneurysms are usually asymptomatic. However, as these aneurysms become larger there is an increased risk for clinical effects, including nausea, dizziness, headaches, vision changes, intracranial hemorrhage, and even death.

5. Purpose • The “gold standard” for identifying cerebral aneurysms remains conventional digital subtraction angiography (DSA). However, this is expensive, time consuming, and invasive. • As such, other imaging modalities such as magnetic resonance angiography (MRA) are employed to evaluate for intracerebral aneurysms. • We found that supraclinoid aneurysms in particular are often difficult to detect utilizing MRA by the method employed at our institution (our routine method includes source images and circle of Willis maximal intensity projections displayed ‘tumbled’ and ‘spun side to side’)

6. Purpose • Our suspicion is that this difficulty is due, in part, to aneurysms in this location being poorly profiled when both right and left sided cerebral arteries are simultaneously displayed on maximum intensity projection (MIP) images, creating overlap in different projections. • Our objective is to evaluate the hypothesis that by showing MIP images of only the right or only the left sided cerebral arteries, similar to how DSAs are obtained, there will be a better detection rate of supraclinoid aneurysms.

8. Materials and Methods • This was a retrospective study in which three different radiologists of varying experience (two board certified neuroradiologists and one neuroradiology fellow) evaluated MRA examinations with and without supraclinoid aneurysms, which had been proven by a previously performed DSA.

9. Materials and Methods • Twenty patients were identified who had a total of 27 supraclinoid aneurysms. • Of the 20 cases positive for supraclinoid aneurysms, 15 patients had one supraclinoid aneurysm, three patients had two supraclinoid aneurysms and two patients had three supraclinoid aneurysms, for 27 total supraclinoid aneurysms.

10. Materials and Methods • We also included 15 patients who had non-supraclinoid aneurysms (ie. basilar tip, anterior communicating, etc.) demonstrated on conventional digital subtraction angiography. • Finally, we included five patients who had no aneurysms in any location, again, proven by DSA.

11. Materials and Methods • The MRA data was anonymized, randomized, and provided to the three reviewers who individually evaluated each study twice.

12. Methods • The exams were reviewed by utilizing the source 3D Time of Flight images in conjunction with whole cerebral arterial MIP images which could be rotated along the transverse or cranial caudal axes. Method A, the routine at our institution.

13. Methods • Additionally , the exams were reviewed by utilizing the source 3D Time of Flight images in conjunction with separate right and left sided cerebral arterial MIP images which could be rotated along the transverse or cranial caudal axes. Method B.

14. Materials and Methods • Reviewers were asked if they found any aneurysms or stenoses or if the study was normal. • If an aneurysm or stenosis was found, the reviewer was asked to name the location. • Results were compared to the previously performed DSA reports for statistical analysis of detection of supraclinoid aneurysms.

16. Results • Summary of the reviewers’ findings in each of the 20 cases with supraclinoid aneurysms, using both method A and method B

17. Results • The following table summarizes the count and percent of aneurysms found, aneurysms missed, and false positives for each method and reviewer.

18. Results • The following table gives the overall averages of each method (all reviewers)

19. Results • Overall, there does not appear to be much evidence that the methods are significantly different. • The majority of findings were identical between the methods. • The ones that differ do not seem to follow any particular pattern (i.e. sometimes A was better, sometimes B was better).

20. Results • The accuracy of the both methods was also assessed. Method A performed better than method B in three total cases between the three reviewers. • Method B on the other hand performed better than Method A in six total cases between the reviewers.

21. Results • Overall, there did not appear to be a statistically significant difference in performance between the two methods in this study; a test of marginal homogeneity has p-value of 0.655 for Reviewer 1, 0.102 for Reviewer 2, 0.782 for Reviewer 3, and 0.414 for the combined data. • This means that we fail to reject the null hypothesis and we cannot definitely conclude that there is any difference between the distribution of correct answers for Methods A and B. • Method B’s results do seem slightlybetter than those of Method A in this study (although not significantly); it is conceivable that Method B is more effective but not enough to detect without a larger sample size.

23. Conclusions • While there was no statistically significant difference between the two methods, more supraclinoid aneurysms were detected utilizing the MIP images that highlighted the left sided and right sided cerebral arteries separately. • These results may be due to the fact that there is no real difference between the two methods. • However, we were limited in the number of cases that we could reasonably ask our observers to review. • It is possible that with a larger sample size this trend of more supraclinoid aneurysms detected with Method B may continue and a statistically significant difference could be proven.

24. Conclusions • It is also possible that the observers performance was affected by their familiarity with Method A, which is the routine way MRA exams are evaluated at our institution. • If Method B became the norm, familiarity could improve the performance of our new method relative to the old. • Additionally, despite our inclusion of distracters (cases of stenosis) to reduce bias, the readers may have developed suspicion that we were targeting supraclinoid aneurysms for the study. This may have increased the detection rate of both methods while decreasing the difference between them. • Lastly, despite anonymizing the data, many of the cases may have been known to the readers if they had previously provided clinical care for the patient. This may also have increased the detection rate of both methods.