Assessment of metallic patient support devices and other items at 7-Tesla: Findings applied to 46 additional devices.

OBJECTIVE: Recently, the first 7-Tesla MR system was approved for clinical use in Europe and the United States. Unfortunately, few metallic objects have undergone testing in association with this high-field-strength scanner, including essential equipment such as patient support devices and other items. Therefore, the objective of this investigation was to assess metallic patient support devices and other items for translational attraction at 7-Tesla. METHODS: Thirteen different metallic items (e.g., gurney, Mayo stand, step stool, utility table, wheelchair, etc.) underwent testing for translational attraction using a previously described methodology in association with a clinical 7-T MR system. The findings were categorized as pass (no translational attraction) or fail (the item was attracted by the scanner). RESULTS: Every metallic item tested exhibited a lack of magnetism while in a worst-case use position and, thus, passed the test for translational attraction in associated with the 7-Tesla MR system. CONCLUSIONS: The different thirteen different metallic patient support devices and other items can be designated as MR Conditional at 7-T or less. Furthermore, because each item represented a worst-case with respect to its mass and the type of metallic material used for its fabrication, the results can be applied to 46 additional smaller items made from the same material or material with a lower magnetic susceptibility. This expanded list of essential patient support devices and other items will facilitate the clinical use of a comparable 7-Tesla scanner, or another UHF scanner with similar fringe field characteristics.

3-Dimensional elastic registration system of prostate biopsy location by real-time 3-dimensional transrectal ultrasound guidance with magnetic resonance/transrectal ultrasound image fusion.

PURPOSE: We determined the accuracy of the novel Urostation 3-dimensional transrectal ultrasound system (Koelis, La Tranche, France) for image based mapping biopsies in a prostate phantom. The system is capable of 1) registering the 3-dimensional location of each biopsy track in the 3-dimensional prostate volume data and 2) performing elastic image fusion of transrectal ultrasound with magnetic resonance imaging. MATERIALS AND METHODS: We used 3 CIRS-053 prostate phantoms containing 3 hypoechoic lesions to perform ultrasound guided biopsy and 3 CIRS-066 phantoms (Computerized Imaging Reference Systems, Norfolk, Virginia) containing 3 isoechoic but magnetic resonance imaging visible lesions to perform magnetic resonance fusion guided biopsy. Three targeted biopsies were done per lesion. Each biopsy tract was injected with gadolinium based magnetic resonance contrast mixed with india ink. Phantoms were then subjected to 1 mm slice magnetic resonance imaging and serial step sectioning to assess the accuracy of targeted biopsy. RESULTS: A total of 27 ultrasound guided biopsies were targeted into 9 hypoechoic lesions. All 27 biopsies (100%) successfully hit the target lesion. For hypoechoic lesions mean ± SD procedural targeting error was 1.52 ± 0.78 mm and system registration error was 0.83 mm, resulting in an overall error of 2.35 mm. Of the 27 magnetic resonance fusion biopsies 24 (84%) hit the lesion. For isoechoic lesions mean procedural targeting error was 2.09 ± 1.28 mm, resulting in an overall error of 2.92 mm. CONCLUSIONS: The novel, computer assisted, 3-dimensional transrectal ultrasound biopsy localization system achieved encouraging accuracy with less than 3 mm error for targeting hypoechoic and isoechoic lesions. The ability to register actual biopsy trajectory and perform elastic magnetic resonance/ultrasound image fusion is a significant advantage for future focal therapy application.

MR spectroscopy in diagnosis and neurological decision-making.

One of the most prolific chemical and anatomical imaging techniques of recent decades, magnetic resonance imaging (MRI), includes the ability to noninvasively assess neurochemical changes with magnetic resonance spectroscopy (MRS). Practical concerns are paramount in applying MRS, such as what the manufacturer provides with a routine MRI scanner, what methods are well tolerated by patients, and what has proved most diagnostically productive over a 25 year span of preliminary exploration of the technology. In this review, the authors explain the technical and neurochemical aspects of MRS and critically discuss its clinical neuroimaging applications.

Ventricular assist device implant (AB 5000) prototype cannula: in vitro assessment of MRI issues at 3-Tesla.

PURPOSE: To evaluate MRI issues at 3-Tesla for a ventricular assist device (VAD). METHODS: The AB5000 Ventricle with a prototype Nitinol wire-reinforced In-Flow Cannula and Out-Flow Cannula attached (Abiomed, Inc., Danvers, MA) was evaluated for magnetic field interactions, heating, and artifacts at 3-Tesla. MRI-related heating was assessed with the device in a gelled-saline-filled, head/torso phantom using a transmit/received RF body coil while performing MRI at a whole body averaged SAR of 3-W/kg for 15-min. Artifacts were assessed for the main metallic component of this VAD (atrial cannula) using T1-weighted, spin echo and gradient echo pulse sequences. RESULTS: The AB5000 Ventricle with the prototype In-Flow Cannula and Out-Flow Cannula attached showed relatively minor magnetic field interactions that will not cause movement in situ. Heating was not excessive (highest temperature change, +0.8 degrees C). Artifacts may create issues for diagnostic imaging if the area of interest is in the same area or close to the implanted metallic component of this VAD (i.e., the venous cannula). CONCLUSION: The results of this investigation demonstrated that it would be acceptable for a patient with this VAD (AB5000 Ventricle with a prototype Nitinol wire-reinforced In-Flow Cannula and Out-Flow Cannula attached) to undergo MRI at 3-Tesla or less. Notably, it is likely that the operation console for this device requires positioning a suitable distance (beyond the 100 Gauss line or in the MR control room) from the 3-Tesla MR system to ensure proper function of the VAD.

Septal repair implants: evaluation of magnetic resonance imaging safety at 3 T.

Specialized implants are used for transcatheter closure of septal defects, including atrial and ventricular septal defects, and patent foramen ovale. These metallic devices may pose a risk to patients undergoing magnetic resonance imaging (MRI) procedures especially if performed at 3 T. Therefore, this investigation evaluated MRI safety at 3 T for septal repair implants (CardioSEAL Septal Repair Implant and STARFlex Septal Repair Implant, NMT Medical, Boston, MA, USA) by characterizing magnetic field interactions, heating and artifacts. These implants exhibited minor magnetic field interactions; heating was not excessive (+0.5 degrees C); and artifacts will only create a problem if the area of interest is in the same area as or near these devices. Thus, the findings indicated that it would be safe for a patient with these implants to undergo MRI at 3 T or lower. Importantly, because of the minor magnetic field interactions, MRI may be performed immediately after implantation.