Prostate MR elastography with transperineal electromagnetic actuation and a fast fractionally encoded steady‐state gradient echo sequence

Abstract

Our aim is to develop a clinically viable, fast-acquisition, prostate MR elastography (MRE) system with transperineal excitation. We developed a new actively shielded electromagnetic transducer, designed to enable quick deployment and positioning within the scanner. The shielding of the transducer was optimized using simulations. We also employed a new rapid pulse sequence that encodes the three-dimensional displacement field in the prostate gland using a fractionally encoded steady-state gradient echo sequence, thereby shortening the acquisition time to a clinically acceptable 8-10 min. The methods were tested in two phantoms and seven human subjects (six volunteers and one patient with prostate cancer). The MRE acquisition time for 24 slices, with an isotropic resolution of 2 mm and eight phase offsets, was 8 min, and the total scan, including positioning and set-up, was performed in 15-20 min. The phantom study demonstrated that the transducer does not interfere with the acquisition process and that it generates displacement amplitudes that exceed 100 µm even at frequencies as high as 300 Hz. In the in vivo human study, average wave amplitudes of 30 µm (46 µm at the apex) were routinely achieved within the prostate gland at 70 Hz. No pain or discomfort was reported. Results in a single patient suggest that MRE can identify cancer tumors, although this result is preliminary. The proposed methods allow the integration of prostate MRE with other multiparametric MRI methods. The results of this study clearly motivate the clinical evaluation of transperineal MRE in patients.

MR elastography to measure the effects of cancer and pathology fixation on prostate biomechanics, and comparison withT1,T2and ADC

“…In this work PZ was found to be stiffer than CG; agreeing with earlier observations (Krouskop et al , 1998; Kemper et al , 2004) (mechanical frequencies: 0.1–4.0 Hz, and 65 Hz respectively). However some in vivo work has reported higher elastic modulus values in the CG compared with the PZ for healthy volunteers (Sahebjavaher et al , 2014) (70 Hz mechanical wave frequency). However (Sahebjavaher et al , 2014) also reported data for a prostate cancer patient for whom E was higher in the PZ compared with the CG.…”

“…However some in vivo work has reported higher elastic modulus values in the CG compared with the PZ for healthy volunteers (Sahebjavaher et al , 2014) (70 Hz mechanical wave frequency). However (Sahebjavaher et al , 2014) also reported data for a prostate cancer patient for whom E was higher in the PZ compared with the CG. (Dresner et al , 1999) used dynamic MRE (mechanical frequency 100–600 Hz) on ex vivo prostate specimens, and found that for non-cancerous prostate the CG was stiffer than PZ, while cancer increased stiffness in the PZ, and also demonstrated that prostate shear modulus increases with the mechanical driving frequency, and therefore prostate tissue exhibits viscoelastic properties.…”

Prostate Cancer: Diagnostic Performance of Real-time Shear-Wave Elastography

“…Recently, MR elastography has also proved capable of providing an elasticity image of the prostate. Although MR imaging shows promise, only a few clinical studies have been performed yet, and these were performed in a limited number of patients (38,39).…”

MR elastography of prostate cancer: quantitative comparison with histopathology and repeatability of methods

“…A shielded electromagnetic transducer was placed against the perineum of the subject in the supine position (13,14), as shown in Fig. 1.…”