Felmlee, Joel P.

MRI guided focused ultrasound (FUS) has been shown to create thermal lesions where tissue stiffness changes significantly. To assess the correlation between tissue stiffness change and tissue ablation, a pilot animal based study was conducted to treat LNCaP tumors in vivo and Hep3B tumors immediately post mortem. MR elastography was used to analyze tissue stiffness before and after ablation. Treated tissue was excised immediately after each experiment and processed by routine histological analysis. Four prostate cancer tumors and four liver cancer tumors showed, on average, a threefold increase in stiffness due to FUS thermal treatment. Histology showed complete (100%) coagulation necrosis in these cases. These data suggest that MRE may be an effective means to assess tissue ablation.

Background: Reliable measurement of subfascial pressures represents an essential part of compartment syndrome management. To date, there is neither consensus on the number or location of foot compartments, nor a standardized protocol for needle placement. The purpose of this study was to devise a new system using 3-Tesla MRI that assesses the number and location of these compartments. Methods: To document the specific location of foot compartments, high resolution 3-Tesla MRI (General Electric, Milwaukee, WI) was coupled with a dedicated transmit-receive high signal-to-noise foot/ankle coil (IGC-Medical Advances, Milwaukee, WI). Individual compartments were highlighted and mapped to T1-weighted MRI. Three-dimensional image analysis allowed standardized needle placement recommendations. Results: Six feet from healthy volunteers were imaged. From these, ten compartments were described: (1) medial, (2) central superficial, (3) central deep (adductor), (4) lateral, (5–8) interossei, (9) calcaneal, and (10) skin. Optimal needle placement and depth were identified. Conclusions: The proposed system allowed us to assess the number and location of foot compartments. Computer image analysis enabled us to define exact points for needle insertion and depth of penetration for accurate pressure monitoring.

In this study, we propose a quality control program for MR‐guided focused ultrasound (FUS) ablation treatment to assess FUS beam positioning accuracy, FUS power delivery accuracy, MR imaging quality, and FUS ablation system safety. A total of 353 sonication points in Lucite cards were measured, the average placement errors were in the SI direction and in the LR direction. Temperature elevation was calculated from MR phase difference images and the measured water proton chemical shift (WPCS) temperature coefficient. WPCS temperature calibration for phantoms yielded a temperature coefficient of 0.011 ppm/°C. Sixteen experiments were conducted using six different phantoms to test the reliability of FUS power delivery. SNR and RF power calculated from phantom images were analyzed and stored at the MR console. A computer program was developed to integrate the system power delivery and the MR image quality control into one automated process. In the clinical trial at our institution, we expect this quality control program to be carried out before each patient treatment. If measured quality control values exceeds or below the preset values, a system service and retest should be conducted before the treatment.PACS number(s): 87.61.–c, 87.54.–n

OBJECTIVE:To assess the magnetic resonance imaging (MRI) safety of titanium middle ear prostheses at 3.0 tesla (T).STUDY DESIGN AND SETTING:Titanium middle ear prostheses from 3 commercial vendors were examined for magnetic field interactions at 3 T. Initially, ex vivo studies were performed to test for rotational motion and forward displacement (translational motion) of the prostheses in a static magnetic field. If movement was observed during this screening study, then the prosthesis was tested to determine the translational or rotational force acting upon the prosthesis. In addition to testing for prosthesis displacement, temperature changes of the prostheses were measured to assess for radiofrequency heating during imaging.RESULTS:Twenty‐one of the 24 titanium prostheses tested revealed no movement when tested in the 3 T static magnetic field. Three prostheses revealed minimal movement during the screening study. A translational force test (string test) was performed upon these 3 prostheses, and the measured angle of displacement was used to determine the force. This calculated force acting upon each prosthesis was essentially zero. Therefore, we conclude that the magnetic field interaction is negligible. A positive control with a ferromagnetic stainless steel prosthesis demonstrated obvious displacement during the screening study, as well as deflection of the prosthesis by 90° in the translational force test. Last, heating of the titanium prostheses did not occur in the 7 models tested.CONCLUSIONS:Middle ear prostheses made from titanium are safe, neither deflecting nor heating during magnetic resonance examinations conducted at 3 T. EBM rating: C‐1.