Safely assessing radiofrequency heating potential of conductive devices using image-based current measurements.

PURPOSE: Many procedures involving catheters and implanted medical devices could benefit from MRI guidance but are currently contraindicated due to risk of significant heating near linear conductive structures. A priori safety prediction is impossible in vivo and thus, safety is typically investigated in vitro by directly measuring temperature rise. Existing methods of investigating safety are inflexible and provide few data. Furthermore, they are fundamentally limited because dangerous temperatures rises can only be investigated if induced. A method of remotely predicting safety is necessary for ensuring safety in patients. THEORY AND METHODS: Electric current induced on the metallic object causes any dangerous heating; thus a remote method of safely characterizing the induced radiofrequency (RF) current distribution would suffice to evaluate safety assuming conservative estimates for local tissue properties. Here we propose a method of analyzing induced phase artifacts seen in low-specific absorption rate characterization images, to determine induced current on an interventional device. This induced current distribution can then be used to predict RF heating behavior under application of any other imaging sequence. RESULTS: This method has been successfully used to reproduce numerical simulations in a phantom. Furthermore, the heating behavior around a conductive wire produced by a scan other than that used to characterize current was successfully predicted. CONCLUSION: It has been shown in phantom experiments that remote current characterization can safely prevent dangerous scans as well as enable safe scans that previously would not have been attempted.

Impact of extended pre-scan written instructions on motion artifacts during head magnetic resonance imaging.

This study aimed to assess the effect of extending pre-scan written instructions to patients undergoing head magnetic resonance imaging (MRI) examinations on motion artifacts. A controlled study was conducted in King Fahad Hospital at the Department of Radiology. A total of 100 patients were involved: 50 received only routine oral hospital instructions (control group), and another 50 received pre-scan extended written instructions besides routine oral hospital instructions (intervention group). The head MRI images were assessed regarding motion artifacts. Informed consent was obtained from all patients included in the study. The incidence of motion artifacts was significantly less in the intervention group than in the control group, 10% and 58%, respectively (p-value=0.001). The motion artifacts decreased significantly in the intervention group compared to the control group. Extending written information before an MRI scan could significantly reduce motion artifacts and improve image quality.

Recommendations of Choice of Head Coil and Prescan Normalize Filter Depend on Region of Interest and Task.

The performance of MRI head coils together with the influence of the prescan normalize filter in different brain regions was evaluated. Functional and structural data were recorded from 26 participants performing motor, auditory, and visual tasks in different conditions: with the 20- and 64-channel Siemens head/neck coil and the prescan normalize filter turned ON or OFF. Data were analyzed with the MRIQC tool to evaluate data quality differences. The functional data were statistically evaluated by comparison of the ß estimates and the time-course signal-to-noise ratio (tSNR) in four regions of interest, i.e., the auditory, visual, and motor cortices and the thalamus. The MRIQC tool indicated a better data quality for both functional and structural data with the prescan normalize filter, with an advantage for the 20-channel head coil in functional data and an advantage for the 64-channel head coil in structural measurements. Nevertheless, recommendations for the functional data regarding choice of head coils and prescan normalize filter depend on the brain regions of interest. Higher ß estimates and tSNR values occurred in the auditory cortex and thalamus with the prescan normalize filter, whereas the contrary was true for the visual and motor cortices. Due to higher ß estimates in the visual cortex in the 64-channel head coil, this head coil is recommended for studies investigating the visual cortex. For most of the research questions, the 20-channel head coil is better suited for functional experiments, with the prescan normalize filter, especially when investigating deep brain areas. For anatomical studies, the 64-channel head coil seemed to be the better choice.

The accuracy of three-dimensional bladder ultrasonography in determining the residual urinary volume compared with conventional catheterisation.

OBJECTIVE: To determine the accuracy of three-dimensional bladder ultrasonography (US, using the BVI 3000, Verathon, WA, USA) for determining the residual urinary volume, compared with the conventional catheterisation method. PATIENTS AND METHODS: We conducted a cross-sectional study at day-care unit of a University hospital after obtaining approval from the Ethics Review Committee of the hospital. Thirty-four patients with lower urinary tract symptoms requiring cystometrography were included. The postvoid volume was measured by bladder US, with three readings taken, and then patient was catheterised using a 12-F Nelaton catheter to measure the urinary volume. The mean of the three readings was compared with the catheterisation volume. RESULTS: The mean (SD) urinary volumes by US and catheterisation were 261 (186) and 260 (175) mL, respectively, and the correlation (r (2)) was 0.97. There was no effect of age, gender or body mass index on the accuracy of bladder US, which was accurate even when the urinary volume was ⩽100 mL. CONCLUSION: The bladder US estimate is as accurate as catheterisation for determining the postvoid residual urinary volume. Its accuracy was also comparable when the urinary volume is <100 mL, and there was no significant effect of age, gender and body mass index. This system could replace the more invasive catheterisation, and with excellent accuracy.