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The purpose of this study is to develop and test a tapping device for needle insertion for prostate brachytherapy. This device will tap the needle into the prostate with a certain, well-defined, amount of momentum, instead of the currently used method of pushing the needle. Because of the high needle insertion velocity, we expect prostate motion and deformation to be less compared to current methods. We measured the momentum that is applied when manually tapping the needle into the prostate and found a mean momentum of 0.50 +/- 0.07 N s. The tapping device is pneumatically driven and we found that the delivered momentum increased linearly with the applied air pressure. The efficacy of the tapping device was tested on a piece of beef, placed on a freely moving and rotating platform. A significant correlation was found between the applied pressure and the rotation and displacement of the beef. Displacements and rotations were minimal for the highest pressure (4 bar) and amounted to only 2 mm and 6 degrees, respectively. Higher air pressures will further reduce displacements and rotations.

Proton resonance frequency shift (PRFS)‐based MR thermometry is hampered by temporal field changes. Temporal changes in the susceptibility distribution lead to field changes and are therefore a possible source of errors. The susceptibility of fat, χfat, is temperature dependent, in the same order of magnitude as the temperature dependence of the chemical shift of water (0.01 ppm/° C). PRFS‐based temperature measurements may therefore be corrupted by non‐local field effects due to temperature induced susceptibility changes in fatty tissue. We performed simulations to quantify the influence of dχfat/dT on PRFS‐based MR temperature maps during thermal interventions in the breast. Susceptibility distributions were calculated for a 3D breast model without and with a stationary Gaussian temperature distribution and a maximum temperature of 57° C. Subsequently, the magnetic field was calculated in Fourier‐domain from these susceptibility distributions. Changes in the magnetic field distribution were quantified b...

We developed a magnetic resonance (MR)-safe tracking catheter using an optical fiber with a light-diffusing tip segment to transport laser energy through the catheter. This energy is converted to a DC current running through a small coil at the catheter tip. Our method is inherently MR-safe since the use of long conducting wires is avoided. The intravoxel dephasing induced by the tip coil was clearly visible for laser powers between 250 mW and 750 mW for all angular positions of the catheter. J. Magn. Reson. Imaging 2001;13:131-135.

We examined the unwanted radiofrequency (RF) heating of an endovascular guidewire frequently used in interventional magnetic resonance imaging (MRI). A Terumo guidewire was partly immersed in an oblong saline bath to simulate an endovascular intervention. The temperature rise of the guidewire tip during an FFE sequence [average specific absorption rate (SAR) = 3.9 W/kg] was measured with a Luxtron fluoroscopic fiber. Starting from 26 degrees C, the guidewire tip reached temperatures up to 74 degrees C after 30 seconds of scanning. Touching the guidewire may cause sudden heating at the point of contact, which in one instance caused a skin burn. The excessive heating of a linear conductor like the guidewire can only be explained by resonating RF waves. The capricious dependencies of this resonance phenomenon on environmental factors have severe consequences for predictability and safety guidelines.