Fast PRF-based MR thermometry using double-echo EPI: in vivo comparison in a clinical hyperthermia setting

Abstract

The results indicate that DEPI can replace slower temperature measurement techniques for PRF-based temperature monitoring during thermal treatments. The higher acquisition speed can be exploited for hot spot localization during regional hyperthermia as well as for temperature monitoring during fast thermal therapies.

Optimization of acoustic radiation force imaging: Influence of timing parameters on sensitivity

“…Tissue displacement was simulated using Equation [2]. The tissue constants were measured in a tissuemimicking gel phantom (14) as described further in this section, and used in the simulations: x max ¼ 6.8 mm, s rise ¼ 4 ms, s decay ¼ 2 ms, T Ã 2 ¼ 65 ms, and D ¼ 10 À6 mm 2 / ms. MEG amplitude was set to G ¼ 40 mT/m and slew rate to 160 mT/(mÁms).…”

“…To measure the ARFI-related mechanical tissue constants of the gel phantom for simulations, several MR-ARFI images were acquired with bipolar MEG and different t offset . The phase in the HIFU focus was plotted as a function of t offset , and the phantom-specific constants x max , s rise , and s decay were calculated from a nonlinear fit according to Equations [1] and [2]. For the measurements, the following parameters were used: MEG duration d ¼ 20 ms, HIFU duration d HIFU ¼ 10 ms, t offset ¼ À15-9 ms (in steps of 2 ms), TE ¼ 30 ms, TR ¼ 150 ms. A long TR was chosen to decrease the HIFU duty cycle (here: 6.7%) to minimize residual heating of the phantom.…”

Specialized volumetric thermometry for improved guidance of MRgFUS in brain

“…Multiple‐slice or volumetric thermometry has been proposed using multi‐slice echo‐planar imaging (EPI) , undersampled 3D EPI , novel slice excitation strategies , or a combination of many techniques . Use of multiple readouts has been shown to reduce geometric shift in 2DFT readouts or to improve robustness to off‐resonance with EPI or spiral trajectories, without compromising thermometry precision.…”

MRI for Noninvasive Thermometry

“…Approximately 40 medical centres worldwide routinely carry out MR-guided thermal treatments when surgical resection is not an option, or has been shown to be less effective [27]. Thermal energy is delivered via a high power laser source coupled to a fibre, usually inserted into the tissue in a minimally invasive way [14], delivered via a high intensity focused ultrasound (HIFU) system [7] or a hyperthermia unit [12], in a non-invasive way, or with an interstitial US [5], radio-frequency (RF) [28] or microwave probe [29], again minimally invasively. Laser and US sources are preferably used in conjunction with MRI.…”

“…The most commonly treated tissue is the liver; however with advances in equipment for delivery of thermal energy [5,7,11,14,28,[30][31][32], accurate temperature monitoring, image reconstruction and automation [3,4,6,8,9,[11][12][13][15][16][17][23][24][25], the possibilities are expanding. Emerging applications include local drug-delivery [112][113][114], epilepsy treatment [9], quality control of red blood cells [115], iron mapping [116], diagnosis of multiple sclerosis [117], and brain abnormalities [118,119] and identification of iron-oxide labelled stem cells [120].…”