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Effects of spatial and temporal resolution for MR image‐guided thermal ablation of prostate with transurethral ultrasound
Author(s) -
Pisani Laura J.,
Ross Anthony B.,
Diederich Chris J.,
Nau William H.,
Sommer F. Graham,
Glover Gary H.,
Butts Kim
Publication year - 2005
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.20339
Subject(s) - image resolution , materials science , temporal resolution , ablation , ultrasound , pixel , prostate , scanner , biomedical engineering , noise (video) , magnetic resonance imaging , signal to noise ratio (imaging) , planar , optics , physics , acoustics , nuclear magnetic resonance , computer science , medicine , radiology , image (mathematics) , artificial intelligence , cancer , computer graphics (images)
Purpose To describe approaches for determining optimal spatial and temporal resolutions for the proton resonance frequency shift method of quantitative magnetic resonance temperature imaging (MRTI) guidance of transurethral ultrasonic prostate ablation. Materials and Methods Temperature distributions of two transurethral ultrasound applicators (90° sectored tubular and planar arrays) for canine prostate ablation were measured via MRTI during in vivo sonication, and agree well with two‐dimensional finite difference model simulations at various spatial resolutions. Measured temperature distributions establish the relevant signal‐to‐noise ratio (SNR) range for thermometry in an interventional MR scanner, and are reconstructed at different resolutions to compare resultant temperature measurements. Various temporal resolutions are calculated by averaging MRTI frames. Results When noise is added to simulated temperature distributions for tubular and planar applicators, the minimum root mean squared (RMS) error is achieved by reconstructing to pixel sizes of 1.9 and 1.7 mm, respectively. In in vivo measurements, low spatial resolution MRTI data are shown to reduce the noise without significantly affecting thermal dose calculations. Temporal resolution of 0.66 frames/minute leads to measurement errors of more than 12°C during rapid heating. Conclusion Optimizing MRTI pixel size entails balancing large pixel SNR gain with accuracy in representing underlying temperature distributions. J. Magn. Reson. Imaging 2005;22:109–118. © 2005 Wiley‐Liss, Inc.