Magnetic resonance angiography with ultrashort echo time evaluates cerebral aneurysm with clip

Usefulness of PETRA-MRA for Postoperative Follow-Up of Stent-Assisted Coil Embolization of Cerebral Aneurysms

Objective

Image evaluation after stent-assisted coil embolization (SAC) for a cerebral aneurysm is difficult with conventional MRA or CTA because of metal artifacts. Pointwise encoding time reduction with radial acquisition (PETRA)-MRA is a noninvasive imaging examination that can reduce metal artifacts. This study aimed to examine whether PETRA-MRA can be used as a follow-up imaging after SAC.

Methods

Twelve patients (eight women and four men; mean age, 66.9 ± 13.2 years) underwent SAC for unruptured aneurysms and were retrospectively evaluated using time-of-flight (TOF)- and PETRA-MRA data from the same follow-up session. Two neurosurgeons independently compared the aneurysm occlusion status and flow visualization score in the stented parent artery (4-point scale, where 4 points represented excellent visualization) between TOF- and PETRA-MRA images. If DSA was performed within 3 months before or after PETRA-MRA, the aneurysm assessment was compared between MRA and DSA. The interobserver agreement for each MRA was evaluated.

Results

Nine of the 12 patients underwent DSA within 3 months before and after TOF- and PETRA-MRA. The aneurysm occlusion status on DSA was more consistent with PETRA-MRA (eight of nine cases) than with TOF-MRA (one of nine cases; P = 0.023). The median visualization score of the stented parent artery was significantly higher for PETRA-MRA (4 [interquartile range {IQR} 3-4]) than for TOF-MRA (1 [IQR 1-1], P = 0.003). The interobserver agreement for evaluation of the aneurysm occlusion status and visualization score of the parent artery for PETRA-MRA were excellent (κ = 0.98 and 0.93, respectively). In one case, PETRA-MRA was able to detect aneurysm recurrence, leading to subsequent retreatment.

Conclusion

PETRA-MRA is a noninvasive examination that can be used to evaluate the occlusion status of aneurysms after SAC and visualize the stented parent artery. PETRA-MRA is useful for repeated follow-up examinations after SAC.

1.5 Tesla Non-ultrashort but Short Echo Time Magnetic Resonance Angiography Describes the Arteries Near a Clipped Cerebral Aneurysm

Cerebral aneurysm and mother artery assessment after clipping is essential to evaluate aneurysm remnant, regrowth, and clip slippage. Usually, cerebral angiography and contrast-enhanced computed tomography angiography (CTA) are used for the evaluation, but they have the side effect of contrast medium and are time-consuming. Time-of-flight magnetic resonance angiography (TOF-MRA) is a non-invasive and fast modality, but clip-induced artifacts limit the signal near the metal clip. Recent ultrashort echo time (UTE)-MRA reduces metal artifacts but its availability is still low worldwide. Therefore, we developed a modified TOF-MRA sequence, named short TE-MRA, using Optima MR 360 1.5T Advance (GE Healthcare Life Sciences, Buckinghamshire, UK). It could describe the artery near the clip using general MRA equipment without recent UTE-MRA technology. We present a subarachnoid hemorrhage patient who underwent short TE-MRA about a year after clipping for the aneurysms at the bilateral internal carotid arteries. Short TE-MRA described the left internal carotid, middle cerebral, and anterior cerebral arteries. The right middle and anterior cerebral arteries were described, but the right internal carotid artery was not. Normal TOF-MRA could not describe them. Without recent UTE-MRA technology, short TE-MRA might be an alternative method for evaluating the artery near the clip. Short TE-MRA can be performed by general MRA equipment with a little time, so it may be helpful until UTE-MRA is widely used. Further research is needed on whether short TE-MRA can describe the aneurysm remnant, regrowth, and clip slippage up to the clinically useful level.

The dataset on the clipped cerebral aneurysm and their radiological findings in three-dimensional computed tomography, time-of-flight magnetic resonance angiography (TOF-MRA), and Pointwise Encoding Time Reduction with Radial Acquisition (PETRA)-MRA

These data present the 141 intracranial arterial branches' visibilities near the 72 cerebral aneurysms in postoperative 58 patients treated with titanium or cobalt-chromium-nickel-molybdenum (CCNM) alloy clips. The visibilities were evaluated using time-of-flight magnetic resonance angiography (TOF-MRA), pointwise encoding time reduction with radial acquisition (PETRA)-MRA, which uses MRA with ultrashort echo time (UTE-MRA) and subtraction technique between saturated and non-saturated images, and three-dimensional computed tomography angiography (3DCTA). We retrospectively acquired the data from the medical records of Suwa Red Cross Hospital. Each method's appearance was compared, and associations between visibility on PETRA-MRA, arterial diameter, clip numbers, clip shapes, clip materials, and amounts of hematoma were summarized. Our article on PETRA-MRA's usefulness for proximal and branched arteries evaluation after cerebral aneurysm clipping [1] was based on these data. This dataset would be useful for reference value for other neurosurgeons or radiologists for further analysis on PETRA-MRA and another UTE-MRA like SILENT-MRA after cerebral aneurysm clipping.

Usefulness of 3 Tesla Ultrashort Echo Time Magnetic Resonance Angiography (UTE-MRA, SILENT-MRA) for Evaluation of the Mother Vessel after Cerebral Aneurysm Clipping: Case Series of 19 Patients

It is important to assess the cerebral arteries near the clip after cerebral aneurysm clipping. Contrast-enhanced computed tomography angiography has side effects of contrast medium and radiation exposure. Time-of-flight magnetic resonance angiography (TOF-MRA) is a fast and non-invasive method, but clip-induced artifact limits the assessment around the clip. Recently, 3 tesla MRA with ultrashort echo time called SILENT MRA (GE Healthcare Life Sciences, UK) has been reported to have the potential to overcome these disadvantages. We herein present consecutive 19 cerebral aneurysm patients treated by clipping and evaluated using SILENT MRA. The 19 patients (15 women and 4 men) underwent TOF-MRA and SILENT MRA during the same scan session. Two neurosurgeons independently assessed the visibility of the mother vessel at the clipping site in TOF-MRA and SILENT MRA. We also investigated the factors related to visibility in SILENT MRA. All patients’ mother vessels were not described in TOF-MRA, and that of 16 patients (84%) were described in SILENT MRA. Overall agreement was 100% in the two neurosurgeons, and the fixed marginal kappa = 1.00 (95% CI: 0.36–1.00). Univariate analysis revealed that larger aneurysm dome and long clip blade length contributed to the visibility of the mother vessel in SILENT MRA. (p = 0.023, 0.007, each). In conclusion, SILENT MRA can be applied for the assessment of the arteries and aneurysm neck remnants near the clip. Using clips with long blade and ligation with its tip would be related to the visibility of the mother vessels in SILENT MRA.

Usefulness of Pointwise Encoding Time Reduction with Radial Acquisition and Subtraction-Based Magnetic Resonance Angiography after Cerebral Aneurysm Clipping

Objective

Time-of-flight magnetic resonance angiography (MRA) is limited by clip-induced artifacts after cerebral aneurysmal clipping. Recently, ultrashort echo time was shown to reduce metal artifacts. We assessed the pointwise encoding time reduction with radial acquisition (PETRA) sequence in subtraction-based MRA as an ultrashort echo time method during follow-up for clipping surgery.

Methods

We retrospectively evaluated 114 branches of 63 aneurysms in 56 patients treated with titanium clips using MRA and 3-dimensional computed tomography angiography. The appearance using each method was compared, and the associations between visibility on PETRA-MRA, clip number and shape, and amount of hematoma were examined. Furthermore, the visibility of the aneurysm remnants and 2 clipping cases with cobalt-chromium-nickel-molybdenum clips were evaluated.

Results

No branches were visible using time-of-flight-MRA, but 79 of 114 branches (69.3%) were visible on PETRA-MRA. PETRA-MRA was effective for follow-up imaging in 33 of 63 aneurysms (52.4%). The median vessel diameters were 1.67 mm (interquartile range, 1.24–2.62 mm) and 0.96 mm (interquartile range, 0.59–1.53 mm) in the visible and invisible groups, respectively. Only the vessel diameter correlated significantly (P < 0.001) with the visibility on PETRA-MRA. A receiver operating characteristic curve for the association between the vessel diameter and visibility on PETRA-MRA showed a cutoff value of 1.26 mm for vessel diameter. Cobalt-chromium-nickel-molybdenum clips produced a strong artifact, even on PETRA-MRA. All 4 residual aneurysms were visible on PETRA-MRA.

Conclusions

PETRA-MRA can be useful for follow-up aneurysm imaging when the diameter of vessels adjacent to the clip exceeds 1.26 mm. However, its usefulness is limited to titanium clips.

Three tesla magnetic resonance angiography with ultrashort echo time describes the arteries near the cerebral aneurysm with clip and the peripheral cerebral arteries

Background:

The assessment of the clipped cerebral aneurysm and the cerebral arteries after the treatment of subarachnoid hemorrhage (SAH) is important to find aneurysm regrowth or postoperative cerebral vasospasm. Usually, contrast-enhanced computed tomography angiography is performed for the evaluation of the arteries, but it has side effects of contrast medium. Time-of-flight magnetic resonance angiography (MRA) is a fast and non-invasive method, but clip-induced artifact limits assessment of the artery in the vicinity of the clip. 1.5T MRA with ultrashort echo time (UTE) reduces metal artifact, but the obtained image is too rough to evaluate the aneurysm remnant, and the description range is too narrow to assess the cerebral vasospasm. We routinely use SIGNA Pioneer 3.0T (GE Healthcare Life Sciences, Buckinghamshire, England) and perform SILENT SCAN with UTE-MRA for the postoperative assessment of the clipped aneurysm and cerebral arteries for SAH patients treated by clipping. It has better image quality and describes arteries with a wide description range, so it possesses the potential to overcome the disadvantages of 1.5T UTE-MRA.

Case Description:

We presented a representative SAH patient who postoperatively underwent 3.0T UTE- MRA after clipping. The artery near the clipped aneurysm was evaluated in detail, and the cerebral arteries were described from the main trunk to the peripheral parts with a wide description range, which enabled the assessment of cerebral vasospasm.

Conclusion:

3.0T UTE-MRA may be helpful for the usual assessment of the arteries after clipping and cerebral vasospasm in the future.