Effect of k‐space‐weighted image contrast and ultrasound focus size on the accuracy of proton resonance frequency thermometry

Abstract

The accuracy and precision of proton resonance frequency temperature measurements from a stack-of-stars acquisition using a sliding KWIC window reconstruction are dependent on the size of the KWIC window and the size and shape of the heated region. The temporal modulation transfer function of KWIC reconstructions for any object size can predict the temporal response to changes in signal being acquired, such as temperature and contrast enhancement.

Simultaneous proton resonance frequency shift thermometry and T1 measurements using a single reference variable flip angle T1 method

“…The experiment setup is shown in Figure . The single reference VFA angle was used in conjunction with a multi‐echo linearly rotated stack‐of‐stars imaging sequence with an in‐plane pseudo‐golden angle increment and reconstructed with a dynamic (KWIC) reconstruction to increase the temporal resolution . The 3D rotated SOS imaging volume was prescribed in a sagittal orientation (voxel size = 1.3 mm isotropic; FOV = 208 × 208 × 20.8 mm; matrix = 160 × 160 × 16; 1514 radial projections; TR = 10.5 ms; TE = ms; readout bandwidth = 1200 Hz/pixel).…”

“…The proton resonance frequency (PRF) shift method has been widely adopted due to its linearity over the temperature range of interest, the constant of proportionality being largely independent of tissue type (except adipose tissue), and its ability to produce temperature maps with the spatial and temporal resolution required to monitor treatments in real time. There have been several successful implementations of fully 3D thermometry methods using the PRF shift thermometry technique . Many FUS treatment targets are surrounded by or have adipose tissue in the near field (e.g., breast, abdominal targets).…”

“…In this work, we describe and implement a single reference VFA method to measure T 1 . The proposed method, when combined with a multi‐echo pseudo golden angle stack of stars (SOS) acquisition and k‐space weighted image contrast (KWIC) reconstruction method, will allow for rapid simultaneous PRF and T 1 thermometry techniques, providing T 1 images with temporal resolution equivalent to that of the magnitude image. This work presents the theory behind single reference VFA T 1 calculations and the optimal sequence parameters for simultaneous PRF and single reference VFA T 1 , determined using Monte Carlo simulations of noisy signal as a function of flip angle.…”

“…There have been several successful implementations of fully 3D thermometry methods using the PRF shift thermometry technique. [12][13][14][15][16][17][18][19][20][21] Many FUS treatment targets are surrounded by or have adipose tissue in the near field (e.g., breast, abdominal targets). PRF thermometry is unable to monitor temperature changes in adipose tissue; therefore, several alternative methods to monitor temperature changes in adipose tissue have been proposed.…”

A variable flip angle golden‐angle‐ordered 3D stack‐of‐radial MRI technique for simultaneous proton resonant frequency shift and T1‐based thermometry

“…The backward‐looking KWIC filter used in this study reduced latency as the radial spokes filling the center of k‐space contained the most recent temperature information. However, it was shown that a symmetric KWIC filter would have the highest temperature accuracy since the temperature error from radial spokes acquired in the past and future would more likely cancel each other out.…”