The development and optimisation of 3D black-blood R2* mapping of the carotid artery wall

PurposeTo develop and optimise a 3D black-blood R₂* mapping sequence for imaging the carotid artery wall, using optimal blood suppression and k-space view ordering.MethodsTwo different blood suppression preparation methods were used; Delay Alternating with Nutation for Tailored Excitation (DANTE) and improved Motion Sensitive Driven Equilibrium (iMSDE) were each combined with a three-dimensional (3D) multi-echo Fast Spoiled GRadient echo (ME-FSPGR) readout. Three different k-space view-order designs: Radial Fan-beam Encoding Ordering (RFEO), Distance-Determined Encoding Ordering (DDEO) and Centric Phase Encoding Order (CPEO) were investigated. The sequences were evaluated through Bloch simulation and in a cohort of twenty volunteers. The vessel wall Signal-to-Noise Ratio (SNR), Contrast-to-Noise Ratio (CNR) and R₂*, and the sternocleidomastoid muscle R₂* were measured and compared. Different numbers of acquisitions-per-shot (APS) were evaluated to further optimise the effectiveness of blood suppression.ResultsAll sequences resulted in comparable R₂* measurements to a conventional, i.e. non-blood suppressed sequence in the sternocleidomastoid muscle of the volunteers. Both Bloch simulations and volunteer data showed that DANTE has a higher signal intensity and results in a higher image SNR than iMSDE. Blood suppression efficiency was not significantly different when using different k-space view orders. Smaller APS achieved better blood suppression.ConclusionThe use of blood-suppression preparation methods does not affect the measurement of R₂*. DANTE prepared ME-FSPGR sequence with a small number of acquisitions-per-shot can provide high quality black-blood R₂* measurements of the carotid vessel wall.     

Neural network enhanced 3D turbo spin echo for MR intracranial vessel wall imaging

PurposeTo improve the signal-to-noise ratio (SNR) and image sharpness for whole brain isotropic 0.5 mm three-dimensional (3D) T₁ weighted (T₁w) turbo spin echo (TSE) intracranial vessel wall imaging (IVWI) at 3 T.MethodsThe variable flip angle (VFA) method enables useful optimization across scan efficiency, SNR and relaxation induced point spread function (PSF) for TSE imaging. A convolutional neural network (CNN) was developed to retrospectively enhance the acquired TSE image with PSF blurring. The previously developed VFA method to increase SNR at the expense of blur can be combined with the presented PSF correction to yield long echo train length (ETL) scan while the acquired image remains high SNR and sharp. The overall approach can enable an optimized solution for accelerated whole brain high-resolution 3D T₁w TSE IVWI. Its performance was evaluated on healthy volunteers and patients.ResultsThe PSF blurred image acquired by a long ETL scan can be enhanced by CNN to restore similar sharpness as a short ETL scan, which outperforms the traditional linear PSF enhancement approach. For accelerated whole brain IVWI on volunteers, the optimized isotropic 0.5 mm 3D T₁w TSE sequence with CNN based PSF enhancement provides sufficient flow suppression and improved image quality. Preliminary results on patients further demonstrated its improved delineation for intracranial vessel wall and plaque morphology.ConclusionThe CNN enhanced VFA TSE imaging enables an overall image quality improvement for high-resolution 3D T₁w IVWI, and may provide a better tradeoff across scan efficiency, SNR and PSF for 3D TSE acquisitions.     

Three-dimensional black-blood T2 mapping with compressed sensing and data-driven parallel imaging in the carotid artery

PurposeTo develop a 3D black-blood T₂ mapping sequence with a combination of compressed sensing (CS) and parallel imaging (PI) for carotid wall imaging.Materials and methodsA 3D black-blood fast-spin-echo (FSE) sequence for T₂ mapping with CS and PI was developed and validated. Phantom experiments were performed to assess T₂ accuracy using a Eurospin Test Object, with different combination of CS and PI acceleration factors. A 2D multi-echo FSE sequence was used as a reference to evaluate the accuracy. The concordance correlation coefficient and Bland-Altman statistics were calculated. Twelve volunteers were scanned twice to determine the repeatability of the sequence and the intraclass correlation coefficient (ICC) was reported. Wall-lumen sharpness was calculated for different CS and PI combinations. Six patients with carotid stenosis > 50% were scanned with optimised sequence. The T₂ maps were compared with multi-contrast images.ResultsPhantom scans showed good correlation in T₂ measurement between current and reference sequence (r = 0.991). No significant difference was found between different combination of CS and PI accelerations (p = 0.999). Volunteer scans showed good repeatability of T₂ measurement (ICC: 0.93, 95% CI 0.84–0.97). The mean T₂ of the healthy wall was 48.0 ± 9.5 ms. Overall plaque T₂ values from patients were 54.9 ± 12.2 ms. Recent intraplaque haemorrhage and fibrous tissue have higher T₂ values than the mean plaque T₂ values (88.1 ± 6.8 ms and 62.7 ± 9.3 ms, respectively).ConclusionThis study demonstrates the feasibility of combining CS and PI for accelerating 3D T₂ mapping in the carotid artery, with accurate T₂ measurements and good repeatability.     

High resolution simultaneous imaging of intracranial and extracranial arterial wall with improved cerebrospinal fluid suppression

PurposeTo develop a technique for three dimensional (3D) high resolution joint imaging of intracranial and extracranial arterial walls with improved cerebrospinal fluid (CSF) suppression and good blood suppression based on T1 weighted sampling perfection with application optimized contrast using different angle evolutions (T1w-SPACE) and to compare this technique (hereafter, iSPACE) with alternating with nutation for tailored excitation (DANTE) prepared SPACE sequence (DANTE-SPACE) for their CSF suppression performance around the mid cerebral arteries (MCA) and blood suppression at carotid arteries.Materials and methodsEight volunteers and twelve patients were prospectively recruited in this institutional review board approved study. A custom designed 32-channel coil set covering the intracranial and extracranial arteries was used for signal reception. Imaging was performed in each subject using DANTE-SPACE and iSPACE. Signal-to-noise ratios (SNR) of the vessel walls at the MCA and carotid arteries, and contrast-to-noise ratios (CNR) between vessel wall and CSF at the MCA and between vessel wall and lumen at carotid arteries from the two sequences were compared.ResultsIn volunteers, contrast between CSF and white matter (surrogate for vessel wall signal) at the M2 segments in iSPACE was 67.9% higher than in DANTE-SPACE. At the carotid region, the SNR of vessel wall in iSPACE was 11.6% higher than DANTE-SPACE while the CNR in iSPACE was 13% higher than DANTE-SPACE. In patients, images with 0.6 mm isotropic resolution were obtained in 7.5 min. iSPACE showed 70.9% improvement in CNR between plaque and CSF at the M2 segments compared to DANTE-SPACE.ConclusionSimultaneous extracranial and intracranial arterial wall imaging using iSPACE improved CSF suppression significantly at the M2 segment of MCA while blood suppression was comparable to DANTE-SPACE. The technique achieved 3D images with 0.6 mm isotropic spatial resolution and took 7.5 min using a custom made coil set. Using this technique, intracranial plaque visualization was improved with no observable image SNR degradation.     

3D black blood MR angiography of the carotid arteries. A simple sequence for plaque hemorrhage and stenosis evaluation

ObjectivesTo evaluate the diagnostic performance of a new three-dimensional T1-weighted turbo-spin-echo sequence (3D T1-w TSE) compared to 3D contrast-enhanced angiography (CE-MRA) for stenosis measurement and compared to 2D T1-w TSE for intra-plaque hemorrhage (IPH) detection.MethodsEighty three patients underwent carotid MRI, using a new elliptic-centric phase encoding T1-weighted 3D TSE sequence in addition to the clinical protocol.Two observers evaluated image quality, presence of flow artifacts, and presence of intra-plaque hemorrhage, and computed the NASCET degree of stenosis for CE-MRA and for the new sequence. Inter-observer agreement and correlation between 3D TSE and CE-MRA for NASCET stenosis was estimated using Cohen's kappa, and correlation using linear regression and Bland-Altman plots.Histology was performed on endarterectomy samples for 18 patients. Sensitivity and specificity of 2D and 3D TSE for IPH diagnosis were computed.Results3D TSE showed better image quality than 2D TSE (p < 0.05). Interobserver agreement was good (kappa ≥ 0.86). Correlation between 3D TSE and CE-MRA was excellent (R = 0.95) for NASCET stenosis. Sensitivity and specificity for IPH diagnosis was 50% and 100% for 2D TSE and 100% and 83% for the 3D TSE.ConclusionsThe new 3D T1-w TSE allows both reliable measures of carotid stenosis, with a slight overestimation compared to CE-MRA (5%), and improved IPH identification, compared to 2D TSE.     

Compressed sensing based simultaneous black- and gray-blood carotid vessel wall MR imaging

ObjectiveIn this study, we sought to demonstrate the blood suppression performance, image quality and morphological measurements for compressed sensing (CS) based simultaneous 3D black- and gray-blood imaging sequence (CS-siBLAG) in carotid vessel wall MR imaging.Materials and methodsSeven healthy volunteers and five patients were recruited. Healthy subjects underwent five CS-siBLAG scans with 1, 2, 3, 4 and 5-fold accelerations. Signal-to-tissue ratio (STR) and contrast-to-tissue ratio (CTR) were computed as the measures of flowing signal suppression performance and the image quality for black-blood imaging of the technique. Vessel lumen area (LA) and wall area (WA) were compared between fully sampled acquisition and each accelerated acquisition. Patients underwent three CS-siBLAG scans with 1, 3 and 5-fold accelerations as well as a 3D time of flight (3D TOF) scan. Two radiologists reviewed the under-sampled black- and gray-blood image quality.ResultsSTR and CTR values obtained with 2 to 5-fold accelerations were not significantly different from those with full acquisition. LA and WA measured at 2 ×, 3 ×, 4 × and 5 × were all highly correlated to the corresponding values at 1 ×. For patients imaging, two radiologists both found that the dual-contrast images at 3 × acceleration exhibited comparable image quality to that of the fully sampled acquisition, and that the images at 5 × exhibited slightly blurred vessel wall and outer vessel wall boundaries.ConclusionBy combining the CS under-sampling pattern and reconstruction, pseudo-centric phase encoding order and dual blood contrast sequences, this technique provides spatially registered black- and gray-blood images and excellent visualization for vessel wall imaging and gray-blood imaging in a short scan time.     

Synthetic T2-weighted images of the lumbar spine derived from an accelerated T2 mapping sequence: Comparison to conventional T2w turbo spin echo

ObjectivesTo evaluate the diagnostic usefulness of synthetic T₂-weighted images of the lumbar spine derived from ten-fold undersampled k-space data using GRAPPATINI, a combination of a model-based approach for rapid T₂ and M₀ quantification (MARTINI) extended by generalized autocalibrating partial parallel acquistion (GRAPPA).Materials and methodsOverall, 58 individuals (26 female, mean age 23.3 ± 8.1 years) were examined at 3 Tesla with sagittal and axial T₂w turbo spin echo (TSE) sequences compared to synthetic T₂₋weighted contrasts derived at identical effective echo times and spatial resolutions. Two blinded readers graded disk degeneration and evaluated the lumbar intervertebral disks for present herniation or annular tear. One reader reassessed all studies after four weeks. Weighted kappa statistics were calculated to assess inter-rater and intra-rater agreement. Also, all studies were segmented manually by one reader to compute contrast ratios (CR) and contrast-to-noise ratios (CNR) of the nucleus pulposus and the annulus fibrosus.ResultsOverall, the CR_T2w was 4.45 ± 1.80 and CR_T2synth was 4.71 ± 2.14. Both correlated (rsp = 0.768;p < 0.001) and differed (0.26 ± 1.38;p = 0.002) significantly. The CNR_T2w was 1.73 ± 0.52 and CNR_T2synth was 1.63 ± 0.50. Both correlated (rsp = 0.875;p < 0.001) and differed (−0.10 ± 0.25;p < 0.001) significantly. The inter-rater agreement was substantial to almost perfect (κ = 0.808–0.925) with the intra-rater agreement also substantial to almost perfect (κ = 0.862–0.963). The area under the curve of the receiver operating characteristics assessing disk herniation or annular tear ranged from 0.787 to 0.892.ConclusionsThis study concludes that synthetic images derived by GRAPPATINI can be used for clinical routine assessment with inter-rater and intra-rater agreements comparable to conventional T₂w TSE.     

A fast screening protocol for carotid plaques imaging using 3D multi-contrast MRI without contrast agent

PurposeTo implement a fast (~ 15 min) MRI protocol for carotid plaque screening using 3D multi-contrast MRI sequences without contrast agent on a 3 Tesla MRI scanner.Materials and methods7 healthy volunteers and 25 patients with clinically confirmed transient ischemic attack or suspected cerebrovascular ischemia were included in this study. The proposed protocol, including 3D T1-weighted and T2-weighted SPACE (variable-flip-angle 3D turbo spin echo), and T1-weighted magnetization prepared rapid acquisition gradient echo (MPRAGE) was performed first and was followed by 2D T1-weighted and T2-weighted turbo spin echo, and post-contrast T1-weighted SPACE sequences. Image quality, number of plaques, and vessel wall thicknesses measured at the intersection of the plaques were evaluated and compared between sequences.ResultsAverage examination time of the proposed protocol was 14.6 min. The average image quality scores of 3D T1-weighted, T2-weighted SPACE, and T1-weighted magnetization prepared rapid acquisition gradient echo were 3.69, 3.75, and 3.48, respectively. There was no significant difference in detecting the number of plaques and vulnerable plaques using pre-contrast 3D images with or without post-contrast T1-weighted SPACE. The 3D SPACE and 2D turbo spin echo sequences had excellent agreement (R = 0.96 for T1-weighted and 0.98 for T2-weighted, p < 0.001) regarding vessel wall thickness measurements.ConclusionThe proposed protocol demonstrated the feasibility of attaining carotid plaque screening within a 15-minute scan, which provided sufficient anatomical coverage and critical diagnostic information. This protocol offers the potential for rapid and reliable screening for carotid plaques without contrast agent.     

Intracranial vessel wall imaging framework – Data acquisition,processing, and visualization

ObjectiveAssessment of vessel walls is an integral part in diagnosis and disease monitoring of vascular diseases such as vasculitis. Vessel wall imaging (VWI), in particular of intracranial arteries, is the domain of Magnetic Resonance Imaging (MRI) – but still remains a challenge. The tortuous anatomy of intracranial arteries and the need for high resolution within clinically acceptable scan times require special technical conditions regarding the hardware and software environments.Materials and methodsIn this work a dedicated framework for intracranial VWI is presented offering an optimized, black-blood 3D T1-weighted post-contrast Compressed Sensing (CS)-accelerated MRI sequence prototype combined with dedicated 3D-GUI supported post-processing tool for the CPR visualization of tortuous arbitrary vessel structures.ResultsUsing CS accelerated MRI sequence, the scanning time for high-resolution 3D black-blood CS-space data could be reduced to under 10 min. These data are adequate for a further processing to extract straightened visualizations (curved planar reformats – CPR). First patient data sets could be acquired in clinical environment.ConclusionA highly versatile framework for VWI visualization was demonstrated utilizing a post-processing tool to extract CPR reformats from high-resolution 3D black-blood CS-SPACE data, enabling simplified and optimized assessment of intracranial arteries in intracranial vascular disorders, especially in suspected intracranial vasculitis, by stretching their tortuous course. The processing time from about 15–20 min per patient (data acquisition and further processing) allows the integration into clinical routine.     

Clinical comparison of single-shot EPI,readout-segmented EPI and TGSE-BLADE for diffusion-weighted imaging of cerebellopontine angle tumors on 3 tesla

ObjectiveThe complex anatomical structures of cerebellopontine angle (CPA) pose a unique challenge to diffusion weighted imaging (DWI). This study aimed to compare the clinical utility of the prototypic 2D turbo gradient- and spin echo-BLADE-DWI (TGSE-BLADE-DWI) with that of readout-segmented echo-planar DWI (RESOLVE-DWI) and single-shot echo-planar DWI (SS-EPI-DWI) to visualize CPA anatomic structures and identify CPA tumors.MethodsA total of 8 volunteers and 36 patients with pathological CPA tumors were enrolled to perform the three DWI sequences at 3 T. Scan time of TGSE-BLADE-DWI, RESOLVE-DWI and SS-EPI-DWI was 5 min 51 s, 5 min 15 s and 1 min 22 s, respectively. Subjective analysis, including visualization of anatomical structures, geometric distortion, ghosting artifacts, lesion conspicuity, diagnostic confidence, and overall image quality of the three DWI sequences were scored and assessed. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and apparent diffusion coefficient (ADC) of CPA tumors were measured and compared.ResultsA total of 39 lesions were identified, TGSE-BLADE-DWI detected all of them, RESOLVE-DWI 36 and SS-EPI-DWI 27. Significant differences were found in all the subjective parameters among the three DWI sequences (all p < 0.001). TGSE-BLADE-DWI was significantly better than RESOLVE-DWI in visualization of CPA anatomical structures, geometric distortion, ghosting artifacts, lesion conspicuity, diagnostic confidence, and overall image quality (all p < 0.01), and RESOLVE-DWI showed significantly superior performance than SS-EPI-DWI in all parameters (all p < 0.001). CNRs and ADCs were not significantly different among the three DWI sequences (p = 0.355, p = 0.590, respectively). No significant differences were detected between TGSE-BLADE-DWI SNR and RESOLVE-DWI SNR (p = 0.058), or TGSE-BLADE-DWI SNR and SS-EPI-DWI SNR (p = 0.155).ConclusionCompared with RESOLVE-DWI and SS-EPI-DWI, TGSE-BLADE-DWI minimized geometric distortions and ghosting artifacts and demonstrated an improved ability for depicting CPA tumors with better lesion conspicuity.SummaryGeometric distortions and ghosting artifacts are found at bone-air interfaces using conventional diffusion-weighted imaging (DWI), which is a challenge for imaging cerebellopontine angle (CPA) tumors. Our study validated that geometric distortions and ghosting artifacts were not present on 2D turbo gradient- and spin-echo-BLADE-DWI scans, making this technique useful for visualizing CPA anatomic structures and diagnosing CPA tumors.     

Three-dimensional turbo-spin-echo amide proton transfer-weighted and intravoxel incoherent motion MR imaging for type I endometrial carcinoma: Correlation with Ki-67 proliferation status

BackgroundTo evaluate 3-dimensional amide proton transfer weighted (APTw) imaging for type I endometrial carcinoma (EC), and investigate correlations of Ki-67 labelling index with APTw and intravoxel incoherent motion (IVIM) imaging.Methods54 consecutive patients suspected of endometrial lesions underwent pelvic APTw and IVIM imaging on a 3 T MR scanner. APTw values and IVIM-derived parameters (Dt, D*, f) were independently measured by two radiologists on 22 postoperative pathological confirmed of type I EC lesions. Results were compared between histological grades and Ki-67 proliferation groups. ROC analysis was performed. Pearson's correlation analysis was performed for APTw values and IVIM-derived parameters with Ki-67 labeling index.ResultsAPTw values and Dt, D*, f of all type I EC were 2.9 ± 0.1%, 0.677 ± 0.027 × 10⁻³ mm²/s, 31.801 ± 11.492 × 10⁻³ mm²/s, 0.179 ± 0.050 with inter-observer ICC 0.996, 0.850, 0.956, 0.995, respectively. APTw values of Ki-67 low-proliferation group (<30%, n = 8) were 2.5 ± 0.2%, significantly lower than the high-proliferation group (>30%, n = 14) with APTw values of 3.1 ± 0.1% (p = 0.016). Area under the curve was 0.768. APTw values of type I EC were moderately positively correlated with Ki-67 labelling index (r = 0.583, p = 0.004). There was no significant difference of Dt (p = 0.843), D* (p = 0.262), f (p = 0.553) between the two groups. No correlation was found between IVIM-derived parameters and Ki-67 labelling index (Dt, p = 0.717; D* p = 0.151; f, p = 0.153).Conclusion3D TSE APTw imaging is a feasible approach for detecting type I EC. Ki-67 labeling index positively moderately correlates with APTw not with IVIM.     

An optimized 3D inversion recovery prepared fast spoiled gradient recalled sequence for carotid plaque hemorrhage imaging at 3.0 T

An optimized 3D inversion recovery prepared fast spoiled gradient recalled sequence (IR FSPGR) on a 3-T scanner for carotid plaque imaging is described. It offers clear blood and fat signal suppression at the carotid artery bifurcation and highlights the regions of carotid plaque affected by hemorrhage at 3 T with high contrast and contrast-to-noise ratio compared with other sequences. It can potentially be used to replace the more traditional noncontrast T₁-weighted 2D black-blood imaging for hemorrhage detection and offers additional benefits of high-resolution 3D volumetric visualization.     

3D spin-lock imaging of human gliomas

We investigated whether the simultaneous use of paramagnetic contrast medium and 3D on-resonance spin lock (SL) imaging could improve the contrast of enhancing brain tumors at 0.1 T. A phantom containing serial concentrations of gadopentetate dimeglumine (Gd-DTPA) in cross-linked bovine serum albumin (BSA) was imaged. Eleven patients with histologically verified glioma were also studied. T₁-weighted 3D gradient echo images with and without SL pulse were acquired before and after a Gd-DTPA injection. SL effect, contrast, and contrast-to-noise ratio (CNR) were calculated for each patient. In the glioma patients, the SL effect was significantly smaller in the tumor than in the white and gray matter both before (p = 0.001, p = 0.025, respectively), and after contrast medium injection (p < 0.001, p < 0.001, respectively). On post-contrast images, SL imaging significantly improved tumor contrast (p = 0.001) whereas tumor CNR decreased slightly (p = 0.024). The combined use of SL imaging and paramagnetic Gd-DTPA contrast agent offers a modality for improving tumor contrast in magnetic resonance imaging (MRI) of enhancing brain tumors. 3D gradient echo SL imaging has also shown potential to increase tissue characterization properties of MR imaging of human gliomas.     

Magnetic resonance neurography of the lumbosacral plexus at 3 Tesla – CSF-suppressed imaging with submillimeter resolution by a three-dimensional turbo spin echo sequence

PurposeTo investigate magnetic resonance neurography (MRN) of the lumbosacral plexus (LSP) with cerebrospinal fluid (CSF) suppression by using submillimeter resolution for three-dimensional (3D) turbo spin echo (TSE) imaging.Materials and methodsUsing extended phase graph (EPG) analysis, the signal response of CSF was simulated considering dephasing from coherent motion for frequency-encoding voxel sizes ranging from 0.3 to 1.3 mm and for CSF velocities ranging from 0 to 4 cm/s. In-vivo MRN included 3D TSE data with frequency encoding parallel to the feet/head axis from 15 healthy adults (mean age: 28.5 ± 3.8 years, 5 females; acquisition voxel size: 2 × 2 × 2 mm³) and 16 pediatric patients (mean age: 6.7 ± 4.1 years, 7 females; acquisition voxel size: 0.7 × 0.7 × 1.4 mm³) acquired at 3 Tesla. Five of the adults were scanned repetitively with changing acquisition voxel sizes (1 × 2 × 2 mm³, 0.7 × 2× 2 mm³, and 0.5 × 2 × 2 mm³). Measurements of the bilateral ganglion of the L5 nerve root, averaged between sides, as well as the CSF in the thecal sac were obtained for all included subjects and compared between adults and pediatric patients and between voxel sizes, using a CSF-to-nerve signal ratio (CSFNR).ResultsAccording to simulations, the CSF signal is reduced along the echo train for moving spins. Specifically, it can be reduced by over 90% compared to the maximum simulated signal for flow velocities above 2 cm/s, and could be most effectively suppressed by considering a frequency-encoding voxel size of 0.8 mm or less. For in-vivo measurements, mean CSFNR was 1.52 ± 0.22 for adults and 0.10 ± 0.03 for pediatric patients (p < .0001). Differences in CSFNR were significant between measurements using a voxel size of 2 × 2 × 2 mm³ and measurements in data with reduced voxel sizes (p ≤ .0012), with submillimeter resolution (particularly 0.5 × 2 × 2 mm³) providing highest CSF suppression.ConclusionsApplying frequency-encoding voxel sizes in submillimeter range for 3D TSE imaging with frequency encoding parallel to the feet/head axis may considerably improve MRN of LSP pathology in adults in the future because of favorable CSF suppression.     

Quantification of intervertebral displacement with a novel MRI-based modeling technique: Assessing measurement bias and reliability with a porcine spine model

The purpose of this study was to develop a novel magnetic resonance imaging (MRI)-based modeling technique for measuring intervertebral displacements. Here, we present the measurement bias and reliability of the developmental work using a porcine spine model. Porcine lumbar vertebral segments were fitted in a custom-built apparatus placed within an externally calibrated imaging volume of an open-MRI scanner. The apparatus allowed movement of the vertebrae through pre-assigned magnitudes of sagittal and coronal translation and rotation. The induced displacements were imaged with static (T₁) and fast dynamic (2D HYCE S) pulse sequences. These images were imported into animation software, in which these images formed a background ‘scene’. Three-dimensional models of vertebrae were created using static axial scans from the specimen and then transferred into the animation environment. In the animation environment, the user manually moved the models (rotoscoping) to perform model-to-‘scene’ matching to fit the models to their image silhouettes and assigned anatomical joint axes to the motion-segments. The animation protocol quantified the experimental translation and rotation displacements between the vertebral models. Accuracy of the technique was calculated as ‘bias’ using a linear mixed effects model, average percentage error and root mean square errors. Between-session reliability was examined by computing intra-class correlation coefficients (ICC) and the coefficient of variations (CV). For translation trials, a constant bias (β₀) of 0.35 (± 0.11) mm was detected for the 2D HYCE S sequence (p = 0.01). The model did not demonstrate significant additional bias with each mm increase in experimental translation (β₁Displacement = 0.01 mm; p = 0.69). Using the T₁ sequence for the same assessments did not significantly change the bias (p > 0.05). ICC values for the T₁ and 2D HYCE S pulse sequences were 0.98 and 0.97, respectively. For rotation trials, a constant bias (β₀) of 0.62 (± 0.12)° was detected for the 2D HYCE S sequence (p < 0.01). The model also demonstrated an additional bias (β₁Displacement) of 0.05° with each degree increase in the experimental rotation (p < 0.01). Using T₁ sequence for the same assessments did not significantly change the bias (p > 0.05). ICC values for the T₁ and 2D HYCE S pulse sequences were recorded 0.97 and 0.91, respectively. This novel quasi-static approach to quantifying intervertebral relationship demonstrates a reasonable degree of accuracy and reliability using the model-to-image matching technique with both static and dynamic sequences in a porcine model. Future work is required to explore multi-planar assessment of real-time spine motion and to examine the reliability of our approach in humans.     

Effect of hybrid of compressed sensing and parallel imaging on the quantitative values measured by 3D quantitative synthetic MRI: A phantom study

IntroductionRecently, three-dimensional (3D) quantitative synthetic magnetic resonance imaging (MRI), which quantifies tissue properties and creates multiple contrast-weighted images, has been enabled by 3D-quantification using an interleaved Look-Locker acquisition sequence with a T2 preparation pulse (3D-QALAS). However, the relatively long scan time has hindered its introduction into clinical practice. A hybrid of compressed sensing and parallel imaging (Compressed sensing-sensitivity encoding: CS-SENSE) can accelerate 3D-QALAS; however, whether CS-SENSE affects the quantitative values acquired by 3D-QALAS remains unexplored. Therefore, this study aimed to examine the effects of reduction factors of CS-SENSE (R_CSS) on the quantitative values derived from 3D-QALAS, by assessing the signal-to-noise ratio (SNR) of the quantitative maps, as well as accuracy (linearity and bias) and repeatability of measured quantitative values.MethodsIn this study, the ISMRM/NIST standardized phantom was scanned on a 1.5-T MRI scanner with 3D-QALAS using R_CSS in the range between 1 and 3, with intervals of 0.2, and between 3 and 10 with intervals of 0.5. The T1, T2, and proton density (PD) values were calculated from the imaging data. For each quantitative value, the SNR, the coefficient of determination (R²) of a linear regression model, the error rate, and the within-subject coefficient of variation (wCV) were calculated for each R_CSS and compared.ResultsWithin the clinically-relevant dynamic range of the brain of T1 and T2 (T1: 200–1400 ms; T2; 50–400 ms) and PD value of 15–100% calculated from 3D-QALAS, the effects of R_CSS on quantitative values was small between 1 and 2.8, with SNR ≧ 10, R² ≧ 0.9, error rate ≦ 10%, and wCV ≦ 10%, except for T2 values of 186.1 and 258.4 ms.ConclusionsCS-SENSE enabled the reduction of the scan time of 3D-QALAS by 63.5% (R_CSS = 2.8) while maintaining the SNR of quantitative maps and accuracy and repeatability of the quantitative values.     

Vessel length on SNAP MRA and TOF MRA is a potential imaging biomarker for brain blood flow

PurposeTo explore feasibility of using the vessel length on time-of-flight (TOF) or simultaneous non-contrast angiography and intraplaque hemorrhage (SNAP) MRA as an imaging biomarker for brain blood flow, by using arterial spin labeling (ASL) perfusion imaging and 3D phase contrast (PC) quantitative flow imaging as references.MethodsIn a population of thirty subjects with carotid atherosclerotic disease, the visible intracranial arteries on TOF and SNAP were semi-automatically traced and the total length of the distal segments was calculated with a dedicated software named iCafe. ASL blood flow was calculated automatically using the recommended hemodynamic model. PC blood flow was obtained by generating cross-sectional arterial images and semi-automatically drawing the lumen contours. Pearson correlation coefficients were used to assess the associations between the different whole-brain or hemispheric blood flow measurements.ResultsUnder the imaging protocol used in this study, TOF vessel length was larger than SNAP vessel length (P < 0.001). Both whole-brain TOF and SNAP vessel length showed a correlation with whole brain ASL and 3D PC blood flow measurements, and the correlation coefficients were higher for SNAP vessel length (TOF vs ASL: R = 0.554, P = 0.002; SNAP vs ASL: R = 0.711, P < 0.001; TOF vs 3D PC: R = 0.358, P = 0.052; SNAP vs 3D PC: R = 0.425, P = 0.019). Similar correlation results were observed for the hemispheric measurements. Hemispheric asymmetry index of SNAP vessel length also showed a significant correlation with hemispheric asymmetry index of ASL cerebral blood flow (R = 0.770, P < 0.001).ConclusionThe results suggest that length of the visible intracranial arteries on TOF or SNAP MRA can serve as a potential imaging marker for brain blood flow.     

Non-contrast MR Lymphography of lipedema of the lower extremities

AimTo assess imaging findings and characteristics of the lymphatic system in patients affected by lipedema and lipolymphedema of the lower extremities on Non-Contrast MR Lymphography (NCMRL).Materials and methods44 lower extremities in 11 consecutive female patients affected by lipedema, and 11 patients with lipolymphedema were examined by NCMRL. MR imaging was performed on 1.5-T system MR equipment. The examination consisted of one 3D short-tau inversion recovery (STIR) and one heavily T2-weighted 3D-Turbo Spin Echo (TSE) sequence.ResultsAll patients showed symmetrical enlargement of the lower extremities with increased subcutaneous fat tissue. The fat tissue was homogeneous, without any signs of edema in pure lipedema patients. In all the extremities with lipolymphedema, high signal intensity areas in the epifascial region could be detected on the 3D-TSE sequence (p < .001) with evidence of mild epifascial fluid collections (p < .001). No sign of honeycomb pattern fat appearance was observed. The appearance of the iliac lymphatic trunks was normal in both lipedema and lipolymphedema patients. Dilated peripheral lymphatics were observed in 2 patients affected by lipedema, indicating a subclinical status of lymphedema, and in 10 patients with lipolymphedema (p = .001). Signs of vascular stasis were observed in both groups, without statistically significant difference (p = .665).ConclusionNCMRL is a non-invasive imaging technique that is suitable for the evaluation of patients affected by lipedema and lipolymphedema, helping in the differential diagnosis.     

Rapid whole-brain quantitative magnetization transfer imaging using 3D selective inversion recovery sequences

Selective inversion recovery (SIR) is a quantitative magnetization transfer (qMT) method that provides estimates of parameters related to myelin content in white matter, namely the macromolecular pool-size-ratio (PSR) and the spin-lattice relaxation rate of the free pool (R_1f), without the need for independent estimates of ∆B₀, B₁⁺, and T₁. Although the feasibility of performing SIR in the human brain has been demonstrated, the scan times reported previously were too long for whole-brain applications. In this work, we combined optimized, short-TR acquisitions, SENSE/partial-Fourier accelerations, and efficient 3D readouts (turbo spin-echo, SIR-TSE; echo-planar imaging, SIR-EPI; and turbo field echo, SIR-TFE) to obtain whole-brain data in 18, 10, and 7 min for SIR-TSE, SIR-EPI, SIR-TFE, respectively. Based on numerical simulations, all schemes provided accurate parameter estimates in large, homogenous regions; however, the shorter SIR-TFE scans underestimated focal changes in smaller lesions due to blurring. Experimental studies in healthy subjects (n = 8) yielded parameters that were consistent with literature values and repeatable across scans (coefficient of variation: PSR = 2.2–6.4%, R_1f = 0.6–1.4%) for all readouts. Overall, SIR-TFE parameters exhibited the lowest variability, while SIR-EPI parameters were adversely affected by susceptibility-related image distortions. In patients with relapsing remitting multiple sclerosis (n = 2), focal changes in SIR parameters were observed in lesions using all three readouts; however, contrast was reduced in smaller lesions for SIR-TFE, which was consistent with the numerical simulations. Together, these findings demonstrate that efficient, accurate, and repeatable whole-brain SIR can be performed using 3D TFE, EPI, or TSE readouts; however, the appropriate readout should be tailored to the application.