Musculoskeletal MRI at 3.0T and 7.0T: A comparison of relaxation times and image contrast

Abstract

OBJECTIVE The purpose of this study was to measure and compare the relaxation times of musculoskeletal tissues at 3.0T and 7.0T, and to use these measurements to select appropriate parameters for musculoskeletal protocols at 7.0T. MATERIALS AND METHODS We measured the T1 and T2 relaxation times of cartilage, muscle, synovial fluid, bone marrow and subcutaneous fat at both 3.0T and 7.0T in the knees of five healthy volunteers. The T1 relaxation times were measured using a spin-echo inversion recovery sequence with six inversion times. The T2 relaxation times were measured using a spin-echo sequence with seven echo times. The accuracy of both the T1 and T2 measurement techniques was verified in phantoms at both magnetic field strengths. We used the measured relaxation times to help design 7.0T musculoskeletal protocols that preserve the favorable contrast characteristics of our 3.0T protocols, while achieving significantly higher resolution at higher SNR efficiency. RESULTS The T1 relaxation times in all tissues at 7.0T were consistently higher than those measured at 3.0T, while the T2 relaxation times at 7.0T were consistently lower than those measured at 3.0T. The measured relaxation times were used to help develop high resolution 7.0T protocols that had similar fluid-to-cartilage contrast to that of the standard clinical 3.0T protocols for the following sequences: proton-density-weighted fast spin-echo (FSE), T2-weighted FSE, and 3D-FSE-Cube. CONCLUSION The T1 and T2 changes were within the expected ranges. Parameters for musculoskeletal protocols at 7.0T can be optimized based on these values, yielding improved resolution in musculoskeletal imaging with similar contrast to that of standard 3.0T clinical protocols.

MR imaging of the temporomandibular joint: comparison between acquisitions at 7.0 T using dielectric pads and 3.0 T

“…It is to note that the visibility of the larger anatomical structures, such as the mandibular condyle, mandibular fossa and inferior pterygoid muscle did not benefit from imaging at 7.0 T. These results are well in line with the assumption that fine anatomical structures cannot be depicted in full detail at 3.0 T, 7,12,19 whereas larger structures do not necessarily benefit from a higher spatial resolution. This observation also might explain why the overall image quality was rated similar for both field strengths.…”

“…When assessing a new sequence with respect to a potential clinical application at a new field strength, it is inherently necessary to optimize the imaging protocol with respect to the different relaxation times of musculoskeletal tissue at different static magnetic field strengths. 19 In the current study, selected sequence parameters, such as TE and TR have been chosen to fit different T 1 and T 2 values of specific tissues. However, it is to note that the TMJ consists of various tissue types with a heterogeneous difference between relaxation times at two different field strengths.…”

“…Although a SNR gain has been demonstrated, 20 residual under-and overtipping effects regarding flip angle distribution might still slightly diminish the actual SNR. Second, the 32-channel head coil used at the 3.0-T system was based on the recently developed dStream system (Philips Healthcare, Best, Netherlands), which digitalizes the acquired signal directly in the receive coil and transports it across broadband fibre optic cables, thus avoiding signal losses and noise pickups, which most likely improved the SNR at 3.0 T. This technique is still not available at 7.0 T. Previously, it has been demonstrated that musculoskeletal tissues yield different relaxation times at 7.0 and 3.0 T. 19 Therefore, the TE and TR of newly designed sequences have to be chosen according to the T 1 and T 2 of different tissue types to evaluate the potential of clinical sequences at different field strengths. 13 In the current study, all parameters have been selected in such a way that the whole SNR increase due to higher static magnetic field strength has been invested in higher spatial resolution while keeping the water-fat shift similar, which was considered most beneficial for MRI of the TMJ.…”

“…The intrinsic T 1 time of soft tissue increases with higher field strength, which typically has to be addressed by longer repetition times (TRs) and subsequently longer acquisition times, increasing the risk of movement artefacts. 19 In addition, different tissue relaxation properties might result in different effects of the higher magnetic field strength on SNR. 13 Furthermore, regarding SNR calculation, most of the commonly used algorithms do not account for the distinct spatial variations of noise levels, which are inter alia introduced by multichannel imaging and provide therefore unreliable results, especially when comparing coils with a different number of receive channels.…”

Bilateral Changes in Deep Tissue Environment After Manual Lymphatic Drainage in Patients with Breast Cancer Treatment-Related Lymphedema

“…[36][37][38][39][40][41][42][43][44] Additionally, concentration of other molecules relevant to lymphatic function will influence the water T 2 . It has been shown that in agarose phantoms water T 2 increases with increasing levels of NaCl.…”