T1, T2 and proton density measurements in the grading of cerebral gliomas

The possibility that cerebral tumours may be graded by measuring T1 or T2 with magnetic resonance (MR) imaging was studied. A consecutive series of patients with subsequently verified gliomas was enrolled, and studied with MR. Patients who had prior surgical, chemotherapeutic or steroid treatment were excluded. Single slice multiple saturation recovery and multiple spin echo techniques were used to measure T1, T2 and proton density in the tumour. In 33 patients with cerebral gliomas there were 5 grade I, 12 grade II, 7 grade III and 9 grade IV. T1 and T2 values tended to be smaller in grade I gliomas than in grades II, III and IV gliomas. Relaxation parameters overlapped considerably in tumours with different grades. Proton density values did not show much change between different grades of gliomas. Relaxation parameters cannot be used to determine tumour grade reliably. Correspondence to: S. Newman     

Optimizing the precision-per-unit-time of quantitative MR metrics: examples for T1, T2, and DTI.

Quantitative MR metrics (e.g., T1, T2, diffusion coefficients, and magnetization transfer ratios (MTRs etc)) are often derived from two images collected with one acquisition parameter changed between them (the "two-point" method). Since a low signal-to-noise-ratio (SNR) adversely affects the precision of these metrics, averaging is frequently used, although improvement accrues slowly-in proportion to the square root of imaging time. Fortunately, the relationship between the images' SNRs and the metric's precision can be exploited to our advantage. Using error propagation rules, we show that for a given sequence, specifying the total imaging time uniquely determines the optimal acquisition protocol. Specifically, instead of changing only one acquisition parameter and repeating the imaging pair until all available time is spent, we propose to adjust all of the parameters and the number of averages at each point according to their contribution to the sought metric's precision. The tactic is shown to increase the precision of the well-known two-point T1, T2, and diffusion coefficients estimation by 13-90% for the same sample, sequence, hardware, and duration. It is also shown that under this general framework, precision accrues faster than the square root of time. Tables of optimal parameters are provided for various experimental scenarios.     

Features of the hypointense solid lesions in the female pelvis on T2‐weighted MRI

Most solid lesions in the female pelvis appearing hyperintense on T2‐weighted images should be interpreted as malignant. In contrast, if the solid lesions in the female pelvis appear hypointense on T2‐weighted images they may be benign. The characteristic imaging features of hyperintense solid lesions in the female pelvis on T2‐weighted images are well known, but various unusual causes and imaging features of hypointense solid lesions in the female pelvis on T2‐weighted images can be particularly misleading. Therefore, careful assessment of hypointense solid lesions in the female pelvis on T2‐weighted images is warranted. In this article, we demonstrate a variety of hypointense solid lesions in the female pelvis on T2‐weighted images. Familiarity with the clinical setting and imaging features of hypointense solid lesions in the female pelvis on T2‐weighted images will facilitate prompt, accurate diagnosis and treatment. J. Magn. Reson. Imaging 2014;39:493–503 . © 2014 Wiley Periodicals, Inc .     

Spatial characterization of T1 and T2 relaxation times and the water apparent diffusion coefficient in rabbit Achilles tendon subjected to tensile loading.

Tendons exhibit viscoelastic mechanical behavior under tensile loading. The elasticity arises from the collagen chains that form fibrils, while the viscous response arises from the interaction of the water with the solid matrix. Therefore, an understanding of the behavior of water in response to the application of a load is crucial to the understanding of the origin of the viscous response. Three-dimensional MRI mapping of rabbit Achilles tendons was performed at 2.0 T to characterize the response of T(1) and T(2) relaxation times and the apparent diffusion coefficient (ADC) of water to tensile loading. The ADC was measured in directions both parallel (ADC( parallel)) and perpendicular (ADC( perpendicular)) to the long axis of the tendon. At a short diffusion time (5.8 ms) MR parameter maps showed the existence of two regions, here termed "core" and "rim", that exhibited statistically significant differences in T(1), T(2), and ADC( perpendicular) under the baseline loading condition. MR parameter maps were also generated at a second loading condition of approximately 1 MPa. At a diffusion time of 5.8 ms, there was a statistically significant increase in the rim region for both ADC( perpendicular) (57.5%) and ADC( parallel) (20.5%) upon tensile loading. The changes in core ADC(( perpendicular), ( parallel)), as well as the relaxation parameters in both core and rim regions, were not statistically significant. The effect of diffusion time on the ADC(( perpendicular), ( parallel)) values was investigated by creating maps at three additional diffusion times (50.0, 125.0, 250.0 ms) using a diffusion-weighted, stimulated-echo (DW-STE) pulse sequence. At longer diffusion times, ADC(( perpendicular), ( parallel)) values increased rather than approaching a constant value. This observation was attributed to T(1) spin-editing during the DW-STE pulse sequence, which resulted in the loss of short-T(1) components (with correspondingly lower ADCs) at longer diffusion times (corroborating the results from earlier spectroscopic work). The T(1) spin-editing effect was observed both in the core and in the rim regions of the tendon and hence was not solely due to the redistribution of water from the core to the rim upon loading. A measure reflective of the regional change in proton density was noted to be consistent with tensile-load-induced water transport from the central to the peripheral tendon region.