Evaluation of a Workflow to Define Low Specific Absorption Rate MRI Protocols for Patients With Active Implantable Medical Devices.

BACKGROUND: MRI exams for patients with MR-conditional active implantable medical devices (AIMDs) are contraindicated unless specific conditions are met. This limits the maximum specific absorption rate (SAR, W/kg). Currently, there is no general framework to guide meeting a lower SAR limit. PURPOSE: To design and evaluate a workflow for modifying MRI protocols to whole-body SAR (WB-SAR ≤0.1 W/kg) and local-head SAR (LH-SAR ≤0.3 W/kg) limits while mitigating the impact on image quality and exam time. STUDY TYPE: Prospective. POPULATION: Twenty healthy volunteers on head (n = 5), C-spine (n = 5), T-spine (n = 5), and L-spine (n = 5) with IRB consent. ASSESSMENT: Vendor-provided head, C-spine, T-spine, and L-spine protocols (SARRT ) were modified to meet both low SAR targets (SARLOW ) using the proposed workflow. in vitro SNR and CNR were evaluated with a T1 -T2 phantom. in vivo image quality and clinical acceptability were scored using a 5-point Likert scale for two blinded readers. FIELD STRENGTH/SEQUENCES: 1.5T/spin-echoes, gradient-echoes. STATISTICAL ANALYSIS: In vitro SNR and CNR values were evaluated with a repeated measures general linear model. in vivo image quality and clinical acceptability were evaluated using a generalized estimating equation analysis (GEE). The two reader's level of agreement was analyzed using Cohen's kappa statistical analysis. RESULTS: Using the workflow, SAR limits were met. LH-SAR: 0.12 ± 0.02 W/kg, median (SD) values for LH-SAR were 0.12 (0.02) W/kg and WB-SAR: 0.09 (0.01) W/kg. Examination time did not increase ≤2x the initial time. SARRT SNR values were higher and significantly different than SARLOW (P < 0.05). However, no significant difference was observed between the CNR values (value = 0.21). Median (IQR) CNR values were 14.2 (25.0) vs. 15.1 (9.2) for head, 12.1 (16.9) vs. 25.3 (14.2) for C-spine, 81.6 (70.1) vs. 71.0 (26.6) for T-spine, and 51.4 (52.6) vs. 37.7 (27.3) for L-spine. Image quality scores were not significantly different between SARRT and SARLOW (median [SD] scores were 4.0 [0.01] vs. 4.3 [0.2], P > 0.05). DATA CONCLUSION: The proposed workflow provides guidance for modifying routine MRI exams to achieve low SAR limits. This can benefit patients referred for an MRI exam with low SAR MR-conditional AIMDs. LEVEL OF EVIDENCE: 1 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2020;52:91-102.

An infundibulum of thalamoperforator arteries: Importance of angiographic images for appropriate diagnosis.

BACKGROUND: The identification of infundibula on noninvasive imaging modalities may be challenging. Because these lesions have generally been viewed as nonpathological, distinguishing them from small or micro-aneurysms is important. CASE DESCRIPTION: A 39-year-old male was diagnosed with recurrence of typical orgasmic headache. An outpoutching arising from the distal part of the right P1 at the take-off of thalamoperforator arteries was visualized on noninvasive investigations. The patient was referred to neurosurgery for surgical management of a right P1 aneurysm. Its unusual location and morphology led to be suspicious of an infundibular dilatation. Catheter angiography with 2D projections and 3D rotational reconstruction revealed an infundibulum at the common origin of two thalamoperforators, giving rise to a double-peaked shape, mimicking a true aneurysm, rather than the more characteristic conical shape of an infundibulum. CONCLUSION: Although noninvasive modalities may identify typical infundibula, the catheter angiogram with 2D projections was critical to establishing the diagnosis. The 3D rotational reconstruction enabled a straightforward understanding of the 3D vascular anatomy. This pyramidal variant of infundibular dilatation should be included in the differential diagnosis of a wide-based nonsaccular arterial contour deformities located in an area of multiple perforators.