Investigative radiology
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Investigative radiology · Jan 2015
Dynamic contrast-enhanced magnetic resonance imaging measurements in renal cell carcinoma: effect of region of interest size and positioning on interobserver and intraobserver variability.
The purpose of this study was to assess the influence of region of interest (ROI) size and positioning on perfusion and permeability parameters as well as on interobserver and intraobserver variability of dynamic contrast-enhanced (DCE-MRI) of primary renal cell carcinoma (RCC) and metastases. ⋯ The ROI size and positioning do substantially influence quantitative perfusion and permeability parameters in DCE-MRI. The best interobserver and intraobserver correlation can be obtained when defining a whole-tumor ROI. The perfusion parameters are the most reliable, whereas the permeability parameters are more susceptible to interobserver variability. No significant differences between placing ROIs on morphological or parametric images were observed.
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Investigative radiology · Jan 2015
Impact of measurement parameters on apparent diffusion coefficient quantification in diffusion-weighted-magnetic resonance imaging.
The scope of this work was to systematically evaluate the reproducibility of diffusion-weighted imaging and the impact of b values used for apparent diffusion coefficient (ADC) calculation as well as the echo time (TE) on the resulting ADC in phantom studies. We attempted to find a minimum upper b value needed for reliable ADC measurements. In addition, we were able to investigate these impacts not only for different diffusivities but also for different T2 relaxation times. The influence of different b values on ADC calculations for different organs was also assessed in a volunteer study. ⋯ Apparent diffusion coefficient can be measured with high reproducibility but strongly depends on b values used and TE, which should be kept constant in each examination protocol. Whereas upper b values as low as 400 s/mm can be used for examinations of tissues with low diffusivities, very high b values (>1000 s/mm) are needed to reach an optimal SNR for high diffusive tissues. An upper b value of 600 s/mm is a good compromise regarding ADC stability, SNR, and measurement time for all tissue types.
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Investigative radiology · Jan 2015
A clinically feasible treatment protocol for magnetic resonance-guided high-intensity focused ultrasound ablation in the liver.
Magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) allows for noninvasive thermal ablation under real-time temperature imaging guidance. The purpose of this study was to assess the feasibility and safety of MR-HIFU ablation of liver tissue in a clinically acceptable setting. The experimental protocol was designed with a clinical ablation procedure of a small malignant tumor in mind; the procedures were performed within a clinically feasible time frame and care was taken to avoid adverse events. The main outcome was the size and quality of the ablated liver tissue volume on imaging and histology. Secondary outcomes were safety and treatment time. ⋯ Our results demonstrate the feasibility and safety of MR-HIFU ablation of liver tissue volumes. The imaging data and cell viability histology show, for the first time, that confluent ablation volumes can be achieved with motion-gated ablation and MR guidance. These results were obtained using a readily available MR-HIFU system with only minor modifications, within a clinically acceptable time frame, and with only minor adverse events. This shows that this technique is sufficiently reliable and safe to initiate a clinical trial.