Simultaneous 3D T 1 $$ {\mathrm{T}}_1 $$ , T 2 $$ {\mathrm{T}}_2 $$ , and fat-signal-fraction mapping with respiratory-motion correction for comprehensive liver tissue characterization at 0.55 T.

PURPOSE: To develop a framework for simultaneous three-dimensional (3D) mapping of T 1 $$ {\mathrm{T}}_1 $$ , T 2 $$ {\mathrm{T}}_2 $$ , and fat signal fraction in the liver at 0.55 T. METHODS: The proposed sequence acquires four interleaved 3D volumes with a two-echo Dixon readout. T 1 $$ {\mathrm{T}}_1 $$ and T 2 $$ {\mathrm{T}}_2 $$ are encoded into each volume via preparation modules, and dictionary matching allows simultaneous estimation of T 1 $$ {\mathrm{T}}_1 $$ , T 2 $$ {\mathrm{T}}_2 $$ , and M 0 $$ {M}_0 $$ for water and fat separately. 2D image navigators permit respiratory binning, and motion fields from nonrigid registration between bins are used in a nonrigid respiratory-motion-corrected reconstruction, enabling 100% scan efficiency from a free-breathing acquisition. The integrated nature of the framework ensures the resulting maps are always co-registered. RESULTS: T 1 $$ {\mathrm{T}}_1 $$ , T 2 $$ {\mathrm{T}}_2 $$ , and fat-signal-fraction measurements in phantoms correlated strongly (adjusted r 2 > 0 . 98 $$ {r}^2>0.98 $$ ) with reference measurements. Mean liver tissue parameter values in 10 healthy volunteers were 427 ± 22 $$ 427\pm 22 $$ , 47 . 7 ± 3 . 3 ms $$ 47.7\pm 3.3\;\mathrm{ms} $$ , and 7 ± 2 % $$ 7\pm 2\% $$ for T 1 $$ {\mathrm{T}}_1 $$ , T 2 $$ {\mathrm{T}}_2 $$ , and fat signal fraction, giving biases of 71 $$ 71 $$ , - 30 . 0 ms $$ -30.0\;\mathrm{ms} $$ , and - 5 $$ -5 $$ percentage points, respectively, when compared to conventional methods. CONCLUSION: A novel sequence for comprehensive characterization of liver tissue at 0.55 T was developed. The sequence provides co-registered 3D T 1 $$ {\mathrm{T}}_1 $$ , T 2 $$ {\mathrm{T}}_2 $$ , and fat-signal-fraction maps with full coverage of the liver, from a single nine-and-a-half-minute free-breathing scan. Further development is needed to achieve accurate proton-density fat fraction (PDFF) estimation in vivo.

Relaxation measurements of an MRI system phantom at low magnetic field strengths.

OBJECTIVE: Temperature controlled T1 and T2 relaxation times are measured on NiCl2 and MnCl2 solutions from the ISMRM/NIST system phantom at low magnetic field strengths of 6.5 mT, 64 mT and 550 mT. MATERIALS AND METHODS: The T1 and T2 were measured of five samples with increasing concentrations of NiCl2 and five samples with increasing concentrations of MnCl2. All samples were scanned at 6.5 mT, 64 mT and 550 mT, at sample temperatures ranging from 10 °C to 37 °C. RESULTS: The NiCl2 solutions showed little change in T1 and T2 with magnetic field strength, and both relaxation times decreased with increasing temperature. The MnCl2 solutions showed an increase in T1 and a decrease in T2 with increasing magnetic field strength, and both T1 and T2 increased with increasing temperature. DISCUSSION: The low field relaxation rates of the NiCl2 and MnCl2 arrays in the ISMRM/NIST system phantom are investigated and compared to results from clinical field strengths of 1.5 T and 3.0 T. The measurements can be used as a benchmark for MRI system functionality and stability, especially when MRI systems are taken out of the radiology suite or laboratory and into less traditional environments.

Dosimetric comparison of MR-linac-based IMRT and conventional VMAT treatment plans for prostate cancer.

BACKGROUND: The aim of this study was to evaluate and compare the performance of intensity modulated radiation therapy (IMRT) plans, planned for low-field strength magnetic resonance (MR) guided linear accelerator (linac) delivery (labelled IMRT MRL plans), and clinical conventional volumetric modulated arc therapy (VMAT) plans, for the treatment of prostate cancer (PCa). Both plans used the original planning target volume (PTV) margins. Additionally, the potential dosimetric benefits of MR-guidance were estimated, by creating IMRT MRL plans using smaller PTV margins. MATERIALS AND METHODS: 20 PCa patients previously treated with conventional VMAT were considered. For each patient, two different IMRT MRL plans using the low-field MR-linac treatment planning system were created: one with original (orig.) PTV margins and the other with reduced (red.) PTV margins. Dose indices related to target coverage, as well as dose-volume histogram (DVH) parameters for the target and organs at risk (OAR) were compared. Additionally, the estimated treatment delivery times and the number of monitor units (MU) of each plan were evaluated. RESULTS: The dose distribution in the high dose region and the target volume DVH parameters (D98%, D50%, D2% and V95%) were similar for all three types of treatment plans, with deviations below 1% in most cases. Both IMRT MRL plans (orig. and red. PTV margins) showed similar homogeneity indices (HI), however worse values for the conformity index (CI) were also found when compared to VMAT. The IMRT MRL plans showed similar OAR sparing when the orig. PTV margins were used but a significantly better sparing was feasible when red. PTV margins were applied. Higher number of MU and longer predicted treatment delivery times were seen for both IMRT MRL plans. CONCLUSIONS: A comparable plan quality between VMAT and IMRT MRL plans was achieved, when applying the same PTV margin. However, online MR-guided adaptive radiotherapy allows for a reduction of PTV margins. With a red. PTV margin, better sparing of the surrounding tissues can be achieved, while maintaining adequate target coverage. Nonetheless, longer treatment delivery times, characteristic for the IMRT technique, have to be expected.

Chronological low field magnetic resonance appearance of canine spinal epidural hemorrhage model.

The magnetic resonance (MR) features of spinal epidural hemorrhage depending with the passage of time have a meaning in veterinary medicine. The aim of this study is to propose the characteristic MR image of spinal epidural hemorrhage using a lower field permanent magnet scanner in dogs. A total of 8 clinically normal beagle dogs, weighing about 9 kg, were allocated. After a baseline MR examination, spinal epidural hemorrhage was created. MR scanning was executed on days 1, 2, 3, 4, 5, 10, 15, 20, 25, and 30 using 0.25 Tesla low field MR. Transverse MR images were attained for image examination. T2W, T1W, fluid-attenuated inversion recovery (FLAIR), short tau inversion recovery (STIR), and T2*-GRE sequences were used. Images were compared subjectively for signal transition assessment. Spinal epidural hemorrhage models were produced positively in 8 dogs at the T12 to L2 region. Initially, the spinal cord and epidural lesions were hyper-intense on T2W and T1W images. On T2W, FLAIR and STIR images, the spinal cord lesion was steadily hyperintense. No significant and consistent hypointense signal indicating hemorrhage was seen on T2*-GRE images. This study result suggests that relatively consistent hyperinstensity on T2 and FLAIR is observed for 30 days, meanwhile T2*-GRE imaging is less useful in hemorrhage detection.

Chronological low field magnetic resonance appearance of canine spinal epidural hemorrhage model

The magnetic resonance (MR) features of spinal epidural hemorrhage depending with the passage of time have a meaning in veterinary medicine. The aim of this study is to propose the characteristic MR image of spinal epidural hemorrhage using a lower field permanent magnet scanner in dogs. A total of 8 clinically normal beagle dogs, weighing about 9 kg, were allocated. After a baseline MR examination, spinal epidural hemorrhage was created. MR scanning was executed on days 1, 2, 3, 4, 5, 10, 15, 20, 25, and 30 using 0.25 Tesla low field MR. Transverse MR images were attained for image examination. T2W, T1W, fluid-attenuated inversion recovery (FLAIR), short tau inversion recovery (STIR), and T2*-GRE sequences were used. Images were compared subjectively for signal transition assessment. Spinal epidural hemorrhage models were produced positively in 8 dogs at the T12 to L2 region. Initially, the spinal cord and epidural lesions were hyper-intense on T2W and T1W images. On T2W, FLAIR and STIR images, the spinal cord lesion was steadily hyperintense. No significant and consistent hypointense signal indicating hemorrhage was seen on T2*-GRE images. This study result suggests that relatively consistent hyperinstensity on T2 and FLAIR is observed for 30 days, meanwhile T2*-GRE imaging is less useful in hemorrhage detection.

The Diagnostic Value of Paramagnetic Contrast Media in MagneticResonance Imaging(MRI)of low Field(A Report of 406 Cases) / 实用放射学杂志

Objective To research paramagnetic contrast media(PCM)dose,injection speed and imaging time etc in low field MRI.Methods 406 patients with lesions spreading all over the body received Gadolinium-DTPA-enhanced scan by bolus injection with the dose of 0.1～0.15 mmol/kg within 60 seconds,and the effects of contrast-enhanced were observed.Results Among 406 patients lesions,337 cases(83%)were enhanced,9 undiscovered lesions displayed enhancement on the precontrast views,5 cases were discovered new lesions in delaying enhancement scan.Conclusion It is safe to apply the above mentioned dose and injection speed in clinic.The side-effects is small,and the development effect is good.It is especially important for lesions involving the structure of the blood brain barrier(BBB).