Non-enhanced MR imaging of cerebral aneurysms: 7 Tesla versus 1.5 Tesla.

PURPOSE: To prospectively evaluate 7 Tesla time-of-flight (TOF) magnetic resonance angiography (MRA) in comparison to 1.5 Tesla TOF MRA and 7 Tesla non-contrast enhanced magnetization-prepared rapid acquisition gradient-echo (MPRAGE) for delineation of unruptured intracranial aneurysms (UIA). MATERIAL AND METHODS: Sixteen neurosurgical patients (male n = 5, female n = 11) with single or multiple UIA were enrolled in this trial. All patients were accordingly examined at 7 Tesla and 1.5 Tesla MRI utilizing dedicated head coils. The following sequences were obtained: 7 Tesla TOF MRA, 1.5 Tesla TOF MRA and 7 Tesla non-contrast enhanced MPRAGE. Image analysis was performed by two radiologists with regard to delineation of aneurysm features (dome, neck, parent vessel), presence of artifacts, vessel-tissue-contrast and overall image quality. Interobserver accordance and intermethod comparisons were calculated by kappa coefficient and Lin's concordance correlation coefficient. RESULTS: A total of 20 intracranial aneurysms were detected in 16 patients, with two patients showing multiple aneurysms (n = 2, n = 4). Out of 20 intracranial aneurysms, 14 aneurysms were located in the anterior circulation and 6 aneurysms in the posterior circulation. 7 Tesla MPRAGE imaging was superior over 1.5 and 7 Tesla TOF MRA in the assessment of all considered aneurysm and image quality features (e.g. image quality: mean MPRAGE7T: 5.0; mean TOF7T: 4.3; mean TOF1.5T: 4.3). Ratings for 7 Tesla TOF MRA were equal or higher over 1.5 Tesla TOF MRA for all assessed features except for artifact delineation (mean TOF7T: 4.3; mean TOF1.5T 4.4). Interobserver accordance was good to excellent for most ratings. CONCLUSION: 7 Tesla MPRAGE imaging demonstrated its superiority in the detection and assessment of UIA as well as overall imaging features, offering excellent interobserver accordance and highest scores for all ratings. Hence, it may bear the potential to serve as a high-quality diagnostic tool for pretherapeutic assessment and follow-up of untreated UIA

Ratings for dome, neck and parent vessel delineation (mean ratings from both readers).

<p>5 =  excellent. 4 =  good. 3 =  moderate. 2 =  poor. and 1 =  non-diagnostic vessel delineation.</p

Basic demographic data and aneurysm size and location.

<p>internal carotid artery (ICA).</p><p>middle cerebral artery (MCA).</p><p>basilar tip (BT).</p><p>posterior cerebral artery (PCA).</p><p>anterior cerebral artery (ACA).</p><p>posterior inferior cerebellar artery (PICA).</p><p>posterior communicating artery (PcomA).</p><p>superior cerebellar artery (SC).</p><p>mean diameter from both readers.</p

Combined readings of both raters for signal intensities of left middle cerebral artery, adjacent gray matter and calculated vessel-tissue contrast ratio for all subjects.

<p>Vessel-tissue contrast ratio of the middle cerebral artery (MCA) were assessed in correlation to surrounding gray matter (GM) for 7 Tesla (T) magnetization prepared rapid acquisition gradient echo (MPRAGE) sequences, 7T time-of-flight (TOF) sequences and for 1.5T TOF sequences. Therefore, regions of interest (ROI) were defined in the largest diameter of the proximal left M1 segments and adjacent gray matter . The average diameter for the ROI of the vessel was 3–5 mm; the ROI for brain parenchyma amounted to approximately 1 cm.</p><p>standard error  = 0.012, 95% confidence interval [0.623 – 0.675].</p><p>standard error =  0.010, 95% confidence interval [0.639 – 0.681].</p><p>standard error =  0.008, 95% confidence interval [0.587 – 0.622].</p

Combined readings of both raters for dome and neck diameter in mm and dome/neck ratio (DNR) for all aneurysms.

<p>standard error  = 0.318, 95% confidence interval [2.098–3.428].</p><p>standard error  = 0.307, 95% confidence interval [2.203–3.489].</p><p>standard error  = 0.299, 95% confidence interval [1.906–3.156].</p

Pulsation artifacts near the carotid bifurcation in TOF MRA scans.

<p>The artifacts in 1.5 Tesla (<b>a</b>) and 7 Tesla (<b>b</b>) TOF MRA scans make vessel depiction more difficult (M1: middle cerebral artery (M1 segment); A1: anterior cerebral artery (A1 segment)).</p

Seventy(subject 5) suffering from basilar tip aneurysm.

<p>White arrows are marking the aneurysm neck, black arrows are marking the aneurysm dome. <b>a:</b> Volume rendering of the 7 Tesla TOF MRA demonstrating the three dimensional structure of the aneurysm; <b>b:</b> transverse plane of the 7 Tesla TOF MRA clearly depicting the aneurysm dome, neck and parent vessel; <b>c:</b> 7 Tesla MPRAGE sequence with excellent delineation of the aneurysm; <b>d:</b> 1.5 Tesla TOF MRA scan with minor irregularities of the parent vessel and aneurysm dome.</p

Ratings for artifacts. vessel-tissue contrast (VTC) and overall image quality (mean ratings from both readers).

<p>5 =  excellent. 4 =  good. 3 =  moderate. 2 =  poor. and 1 =  non-diagnostic vessel delineation.</p

Interobserver accordance (kappa-statistic).

<p><b>According to Landis the kappa coefficient (k) was rated as follows:</b></p><p>Poor (k<0.00), Slight (k = 0.00–0.20), Fair (k = 0.21–0.40), Moderate (k = 0.41–0.60).</p><p>Substantial (k = 0.61–0.80), Almost Perfect (k = 0.81–1.00).</p><p>Disagreements were weighted by 1– {(i–j)/(k–1)}2 where i and j index the rows and columns of the ratings by the two raters and k is the maximum number of possible ratings.</p

Forty-five years old male patient (subject 6) with partially thrombosed left sided fusiform posterior cerebral artery aneurysm.

<p>White arrows are marking the aneurysm neck, black arrows are marking the aneurysm dome. p1: posterior cerebral artery (p1 segment) <b>a:</b> Volume rendering of the 7 Tesla TOF MRA illustrating the three dimensional structure of the aneurysm (ba: basilar artery; sc: superior cerebellar artery; p2: posterior cerebral artery (p2 segment); ab: aneurysm body); <b>b:</b> transverse plane of the 7 Tesla TOF MRA depicting the parent vessel and part of the aneurysm body; <b>c:</b> Excellent delineation of parent vessel and part of the aneurysm body in 7 Tesla MPRAGE scan; <b>d:</b> Moderate depiction of parent vessel and aneurysm body in 1.5 Tesla TOF MRA.</p