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.     

High-resolution,three-dimensional diffusion-weighted breast imaging using DESS

PurposeTo evaluate the use of the double-echo steady-state (DESS) sequence for acquiring high-resolution breast images with diffusion and T2 weighting.Materials and MethodsPhantom scans were used to verify the T2 and diffusion weighting of the DESS sequence. Image distortion was evaluated in volunteers by comparing DESS images and conventional diffusion-weighted images (DWI) to spoiled gradient-echo images. The DESS sequence was added to a standard clinical protocol, and the resulting patient images were used to evaluate overall image quality and image contrast in lesions.ResultsThe diffusion weighting of the DESS sequence can be easily modulated by changing the spoiler gradient area and flip angle. Radiologists rated DESS images as having higher resolution and less distortion than conventional DWI. Lesion-to-tissue contrast ratios are strongly correlated between DWI and DESS images (R = 0.83) and between T2-weighted fast spin-echo and DESS images (R = 0.80).ConclusionThe DESS sequence is able to acquire high-resolution 3D diffusion- and T2-weighted images in short scan times, with image quality that facilitates morphological assessment of lesions.     

Clinical feasibility of 3D-QALAS – Single breath-hold 3D myocardial T1- and T2-mapping

PurposeTo investigate the in-vivo precision and clinical feasibility of 3D-QALAS - a novel method for simultaneous three-dimensional myocardial T1- and T2-mapping.MethodsTen healthy subjects and 23 patients with different cardiac pathologies underwent cardiovascular 3 T MRI examinations including 3D-QALAS, MOLLI and T2-GraSE acquisitions. Precision was investigated in the healthy subjects between independent scans, between dependent scans and as standard deviation of consecutive scans. Clinical feasibility of 3D-QALAS was investigated for native and contrast enhanced myocardium in patients. Data were analyzed using mean value and 95% confidence interval, Pearson correlation, Paired t-tests, intraclass correlation and Bland-Altman analysis.ResultsAverage myocardial relaxation time values and SD from eight repeated acquisitions within the group of healthy subjects were 1178 ± 18.5 ms (1.6%) for T1 with 3D-QALAS, 52.7 ± 1.2 ms (2.3%) for T2 with 3D-QALAS, 1145 ± 10.0 ms (0.9%) for T1 with MOLLI and 49.2 ± 0.8 ms (1.6%) for T2 with GraSE.Myocardial T1 and T2 relaxation times obtained with 3D-QALAS correlated very well with reference methods; MOLLI for T1 (r = 0.994) and T2-GraSE for T2 (r = 0.818) in the 23 patients. Average native/post-contrast myocardial T1 values from the patients were 1166.2 ms/411.8 ms for 3D-QALAS and 1174.4 ms/438.9 ms for MOLLI. Average native myocardial T2 values from the patients were 53.2 ms for 3D-QALAS and 54.4 ms for T2-GraSE.ConclusionsRepeated independent and dependent scans together with the intra-scan repeatability, demonstrated all a very good precision for the 3D-QALAS method in healthy volunteers. This study shows that 3D T1 and T2 mapping in the left ventricle is feasible in one breath hold for patients with different cardiac pathologies using 3D-QALAS.     

Quantitative Dixon MRI sequences to relate muscle atrophy and fatty degeneration with range of motion and muscle force in brachial plexus injury

BackgroundAssessment of muscle atrophy and fatty degeneration in brachial plexus injury (BPI) could yield valuable insight into pathophysiology and could be used to predict clinical outcome. The objective of this study was to quantify and relate fat percentage and cross-sectional area (CSA) of the biceps to range of motion and muscle force of traumatic brachial plexus injury (BPI) patients.MethodsT1-weighted TSE sequence and three-point Dixon images of the affected and non-affected biceps brachii were acquired on a 3 Tesla magnetic resonance scanner to determine the fat percentage, total and contractile CSA of 20 adult BPI patients. Regions of interest were drawn by two independent investigators to determine the inter-observer reliability. Paired Students' t-test and multivariate analysis were used to relate fat percentage, total and contractile CSA to active flexion and biceps muscle force.ResultsThe mean fat percentage 12 ± 5.1% of affected biceps was higher than 6 ± 1.0% of the non-affected biceps (p < 0.001). The mean contractile CSA 8.1 ± 5.1 cm² of the affected biceps was lower than 19.4 ± 4.9 cm² of the non-affected biceps (p < 0.001). The inter-observer reliability was excellent (ICC 0.82 to 0.96). The contractile CSA contributed most to the reduction in active flexion and muscle force.ConclusionQuantitative measurement of fat percentage, total and contractile CSA using three-point Dixon sequences provides an excellent reliability and relates with active flexion and muscle force in BPI.     

Colorectal carcinoma: Ex vivo evaluation using 3-T high-spatial-resolution quantitative T2 mapping and its correlation with histopathologic findings

PurposeIn this study, we aimed to evaluate the feasibility of determining the mural invasion depths of colorectal carcinomas using high-spatial-resolution (HSR) quantitative T2 mapping on a 3-T magnetic resonance (MR) scanner.Materials and methodsTwenty colorectal specimens containing adenocarcinomas were imaged on a 3-T MR system equipped with a 4-channel phased-array surface coil. HSR quantitative T2 maps were acquired using a spin-echo sequence with a repetition time/echo time of 7650/22.6–361.6 ms (16 echoes), 87 × 43.5-mm field of view, 2-mm section thickness, 448 × 224 matrix, and average of 1. HSR fast-spin-echo T2-weighted images were also acquired. Differences between the T2 values (ms) of the tumor tissue, colorectal wall layers, and fibrosis were measured, and the MR images and histopathologic findings were compared.ResultsIn all specimens (20/20, 100%), the HSR quantitative T2 maps clearly depicted an 8-layer normal colorectal wall in which the T2 values of each layer differed from those of the adjacent layer(s) (P < 0.001). Using this technique, fibrosis (73.6 ± 9.4 ms) and tumor tissue (104.2 ± 6.4 ms) could also be clearly differentiated (P < 0.001). In 19 samples (95%), the HSR quantitative T2 maps and histopathologic data yielded the same findings regarding the tumor invasion depth.ConclusionsOur results indicate that 3-T HSR quantitative T2 mapping is useful for distinguishing colorectal wall layers and differentiating tumor and fibrotic tissues. Accordingly, this technique could be used to determine mural invasion by colorectal carcinomas with a high level of accuracy.     

Comparison of 7 T and 3 T MRI in patients with moyamoya disease

Magnetic resonance imaging and magnetic resonance angiography (MRI/MRA) are widely used for evaluating the moyamoya disease (MMD). This study compared the diagnostic accuracy of 7 Tesla (T) and 3 T MRI/MRA in MMD. In this case control study, 12 patients [median age: 34 years; range (10–66 years)] with MMD and 12 healthy controls [median age: 25 years; range (22–59 years)] underwent both 7 T and 3 T MRI/MRA. To evaluate the accuracy of MRI/MRA in MMD, five criteria were compared between imaging systems of 7 T and 3 T: Suzuki grading system, internal carotid artery (ICA) diameter, ivy sign, flow void of the basal ganglia on T2-weighted images, and high signal intensity areas of the basal ganglia on time-of-flight (TOF) source images. No difference was observed between 7 T and 3 T MRI/MRA in Suzuki stage, ICA diameter, and ivy sign score; while, 7 T MRI/MRA showed a higher detection rate in the flow void on T2-weighted images and TOF source images (p < 0.001). Receiver operating characteristic curves of both T2 and TOF criteria showed that 7 T MRI/MRA had higher sensitivity and specificity than 3 T MRI/MRA. Our findings indicate that 7 T MRI/MRA is superior to 3 T MRI/MRA for the diagnosis of MMD in point of detecting the flow void in basal ganglia by T2-weighted and TOF images.     

Clinical value of routine use of thin-section 3D MRI using 3D FSE sequences with a variable flip angle technique for internal derangements of the knee joint at 3T

PurposeTo determine the clinical value of routine use of thin-section 3D MRI using 3D FSE sequences with a variable flip angle technique for internal derangements of the knee joint at 3 T.Method and MaterialsThirty-four knees in 34 patients suspected of having internal derangements of the knee joint were included. Following standard 2D MRI protocol including sagittal PDWI, T1WI and T2*WI, coronal fat-suppressed PDWI, and axial fat-suppressed PDWI with 3-4 mm thicknesses, fat-suppressed and water-excitation PDWI using 3D FSE sequences with a variable flip angle technique with 0.6 mm thickness were obtained in coronal plane and the three major planes with 1 mm thickness (3D MRI) was reformatted. The standard 2D MRI protocol and reformatted 3D MRI protocol (three sagittal 2D sequence images plus 3D MRI) were independently analyzed by two radiologists concerning presence or absence of lesions in the menisci, cartilage, and ligament. Interobserver agreements in both the MRI protocols were assessed by weighted-kappa coefficients. Regarding diagnostic accuracy, areas under the receiver operating characteristic curves (Az values) of both the MRI protocols were compared.ResultsThirty-eight meniscal lesions, 39 cartilage lesions, and 20 ligamentous lesions were surgically detected. Excellent interobserver agreements (kappa = 0.91–0.98) were seen in both the MRI protocols, with a slightly better tendency in the reformatted 3D MRI protocol. Average Az values in detection of the meniscal, cartilage, and ligamentous lesions were significantly higher in the reformatted 3D MRI protocol than in the standard 2D MRI protocol (p < 0.01 or p < 0.001).ConclusionRoutine use of reformatted thin-section 3D MRI using 3D FSE sequences with a variable flip angle technique may improve diagnostic accuracy and confidence in detection of internal derangements of the knee joint.     

3D late gadolinium enhanced cardiovascular MR with CENTRA-PLUS profile/view ordering: Feasibility of right ventricular myocardial damage assessment using a swine animal model

AimsTo develop a high-resolution, 3D late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (MRI) technique for improved assessment of myocardial scars, and evaluate its performance against 2D breath-held (BH) LGE MRI using a surgically implanted animal scar model in the right ventricle (RV).Methods and resultsA k-space segmented 3D LGE acquisition using CENTRA-PLUS (Contrast ENhanced Timing Robust Acquisition with Preparation of LongitUdinal Signal; or CP) ordering is proposed. 8 pigs were surgically prepared with cardiac patch implantation in the RV, followed in 60 days by 1.5 T MRI. LGE with Phase-Sensitive Inversion Recovery (PSIR) were performed as follows: 1) 2DBH using pneumatic control, and 2) navigator-gated, 3D free-breathing (3DFB)-CP-LGE with slice-tracking. The animal heart was excised immediately after cardiac MR for scar volume quantification. RV scar volumes were also delineated from the 2DBH and 3DFB-CP-LGE images for comparison against the surgical standard. Apparent scar/normal tissue signal-to-noise ratio (aSNR) and contrast-to-noise ratio (aCNR) were also calculated.3DFB-CP-LGE technique was successfully performed in all animals. No difference in aCNR was noted, but aSNR was significantly higher using the 3D technique (p < 0.05). Against the surgical reference volume, the 3DFB-CP-LGE-derived delineation yielded significantly less volume quantification error compared to 2DBH-derived volumes (15 ± 10% vs 55 ± 33%; p < 0.05).ConclusionCompared to conventional 2DBH-LGE, 3DFB-LGE acquisition using CENTRA-PLUS provided superior scar volume quantification and improved aSNR.     

Towards intrinsic R2* imaging in the prostate at 3 and 7 tesla

PurposeHypoxia is an important marker for resistance to therapy. In this study, we quantify the macroscopic effects of R2* mapping in prostate cancer patients incorporating susceptibility matching and field strengths effects.Materials and methods91 patients were scanned without endorectal coil (ERC) at 3 T. Only when rectal gas was absent, data was included for analysis. Another group of 10 patients was scanned using a susceptibility matched ERC. To assess the residual contamination of R2 and macroscopic field non-uniformities, a group of 10 patients underwent ultra-high resolution 7 T MRI.ResultsOf the patients scanned at 3 T 60% presented rectal gas and were excluded, due to susceptibility artifacts. At 3 T the tumor was significantly different (P < 0.01) from the healthy surrounding tissue in R2* values at intrapatient level. Using the measured median R2* value of 24.9 s^− 1 at 3 T and 43.2 s^− 1 at 7 T of the peripheral zone, the minimum contribution of macroscopic susceptibility effects is 15% at 3 T.ConclusionR2* imaging might be a promising tool for hypoxia imaging, particularly when minimizing macroscopic susceptibility effects contaminating intrinsic R2* of tissue, such as rectal gas. At 3 T macroscopic effects still contribute 15% in the R2* value, compared to ultra-high resolution R2* mapping at 7 T.     

4D cardiac imaging at clinical 3.0 T provides accurate assessment of murine myocardial function and viability

ObjectivesWe validate a 4D strategy tailored for 3 T clinical systems to simultaneously quantify function and infarct size in wild type mice after ischemia/reperfusion, with improved spatial and temporal resolution by comparison to previous published protocols using clinical field MRI systems.MethodsC57BL/6J mice underwent 60 min ischemia/reperfusion (n = 14) or were controls without surgery (n = 6). Twenty-four hours after surgery mice were imaged with gadolinium injection and sacrificed for post-mortem MRI and histology with serum also taken for Troponin I levels. The double ECG- and respiratory-triggered 3D FLASH (Fast Low Angle Shot) gradient echo (GRE) cine sequence had an acquired isotropic resolution of 344 μm, TR/TE of 7.8/2.9 ms and acquisition time 25–35 min. The conventional 2D FLASH cine sequence had the same in-plane resolution of 344 μm, 1 mm slice thickness and TR/TE 11/5.4 ms for an acquisition time of 20–25 min plus 5 min for planning. Left ventricle (LV) and right ventricle (RV) volumes were measured and functional parameters compared 2D to 3D, left to right and for inter and intra observer reproducibility. MRI infarct volume was compared to histology.ResultsFor the function evaluation, the 3D cine outperformed 2D cine for spatial and temporal resolution. Protocol time for the two methods was equivalent (25–35 min). Flow artifacts were reduced (p = 0.008) and epi/endo-cardial delineation showed good intra and interobserver reproducibility. Paired t-test comparing ejection volume left to right showed no significant difference for 3D (p = 0.37), nor 2D (p = 0.30) and correlation slopes of left to right EV were 1.17 (R² = 0.75) for 2D and 1.05 (R² = 0.50) for 3D.Quantifiable ‘late gadolinium enhancement’ infarct volume was seen only with the 3D cine and correlated to histology (R² = 0.89). Left ejection fraction and MRI-measured infarct volume correlated (R² > 0.3).ConclusionsThe 4D strategy, with contrast injection, was validated in mice for function and infarct quantification from a single scan with minimal slice planning.     

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.     

The effect of morphological and microstructural integrity of the corpus callosum on cognition,fatigue and depression in mildly disabled MS patients

AimTo assess the value of callosal morphological and microstructural integrity in assessing different cognitive domains, fatigue and depression in mildly disabled multiple sclerosis (MS) patients.Materials and methodsWe assessed 29 mildly disabled MS patients and 15 healthy controls using 3T magnetic resonance images (T1-weighted, FLAIR and DTI) and neuropsychological tests assessing different cognitive functions, depression and fatigue. We compared the added value of morphological measures (corpus callosum area corrected for total intracranial volume, index, circularity and the more detailed thickness profile) and diffusion features (fractional anisotropy and mean diffusivity) in multilinear models including standard clinical and whole-brain parameters in assessing neuropsychological scores.ResultsEven in mildly disabled MS patients, a significant reduction of the corpus callosum (p < 0.001) was observed in comparison to healthy controls. Callosal area, index and circularity were significantly (p < 0.002) related to whole-brain white matter volume, T2 lesion load and deep grey matter volume, but not with cortical grey matter.The combination of commonly used imaging and clinical parameters explained between 7% (Fatigue) and 50% (processing speed, verbal memory) of the adjusted variance. Inclusion of the mean diffusivity increased the adjusted R² significantly to 69% (p = 0.004) and 71% (p = 0.002) for visuospatial and verbal memory respectively.ConclusionOur results show that callosal features may be used as an alternative to measuring whole-brain volumes. Furthermore, the microstructural integrity of the corpus callosum can help to predict an MS patient's memory performance.     

Diagnostic accuracy of automatic normalization of CBV in glioma grading using T1- weighted DCE-MRI

PurposeAim of this retrospective study was to compare diagnostic accuracy of proposed automatic normalization method to quantify the relative cerebral blood volume (rCBV) with existing contra-lateral region of interest (ROI) based CBV normalization method for glioma grading using T1-weighted dynamic contrast enhanced MRI (DCE-MRI).Material and methodsSixty patients with histologically confirmed gliomas were included in this study retrospectively. CBV maps were generated using T1-weighted DCE-MRI and are normalized by contralateral ROI based method (rCBV_contra), unaffected white matter (rCBV_WM) and unaffected gray matter (rCBV_GM), the latter two of these were generated automatically. An expert radiologist with > 10 years of experience in DCE-MRI and a non-expert with one year experience were used independently to measure rCBVs. Cutoff values for glioma grading were decided from ROC analysis. Agreement of histology with rCBV_WM, rCBV_GM and rCBV_contra respectively was studied using Kappa statistics and intra-class correlation coefficient (ICC).ResultThe diagnostic accuracy of glioma grading using the measured rCBV_contra by expert radiologist was found to be high (sensitivity = 1.00, specificity = 0.96, p < 0.001) compared to the non-expert user (sensitivity = 0.65, specificity = 0.78, p < 0.001). On the other hand, both the expert and non-expert user showed similar diagnostic accuracy for automatic rCBV_WM (sensitivity = 0.89, specificity = 0.87, p = 0.001) and rCBV_GM (sensitivity = 0.81, specificity = 0.78, p = 0.001) measures. Further, it was also observed that, contralateral based method by expert user showed highest agreement with histological grading of tumor (kappa = 0.96, agreement 98.33%, p < 0.001), however; automatic normalization method showed same percentage of agreement for both expert and non-expert user. rCBV_WM showed an agreement of 88.33% (kappa = 0.76,p < 0.001) with histopathological grading.ConclusionIt was inferred from this study that, in the absence of expert user, automated normalization of CBV using the proposed method could provide better diagnostic accuracy compared to the manual contralateral based approach.     

Intravoxel incoherent motion diffusion-weighted imaging as an adjunct to dynamic contrast-enhanced MRI to improve accuracy of the differential diagnosis of benign and malignant breast lesions

PurposeTo investigate the value of use of intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) as an adjunct to dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to distinguish benign from malignant breast lesions.Materials and methodsRetrospective analysis of data pertaining to 117 patients with breast lesions who underwent DCE-MRI and IVIM-DWI examination with 3.0 T MRI was conducted. A total of 128 lesions were pathologically confirmed (47 benign and 81 malignant). Between-group differences in DCE-MRI parameters (Morphology, enhancement pattern, maximum slope of increase (MSI) and time–signal curve (TIC) type) and IVIM-DWI parameters (f value, D value and D* value) were assessed. Multivariate logistic regression was performed to identify variables that distinguished benign from malignant breast lesions. The diagnostic performance of DCE-MRI and DCE-MRI plus IVIM-DWI, to distinguish benign from malignant breast lesions, was evaluated using pathology results as the gold standard.ResultsLesion morphology, MSI, and TIC type (P < 0.05), but not the enhancement pattern (P > 0.05), were significantly different between the benign and malignant groups. The f (8.53 ± 2.14) and D* (7.64 ± 2.07) values in the malignant group were significantly higher than those in the benign group (7.68 ± 1.97 and 6.83 ± 2.13, respectively), while the D value (0.99 ± 0.22) was significantly lower than that (1.34 ± 0.17) in the benign group (P < 0.05 for all). On logistic regression analysis, the sensitivity, specificity and accuracy of DCE-MRI were 90.1%, 70.2% and 82.8% respectively; the corresponding figures for the combination of IVIM-DWI and DCE-MRI were 88.8%, 85.1%, and 87.5%respectively.ConclusionIVIM-DWI method as an adjunct to DCE-MRI can improve the specificity and accuracy in differential diagnosis of benign and malignant lesions of breast.     

Reduced distortion artifact whole brain CBF mapping using blip-reversed non-segmented 3D echo planar imaging with pseudo-continuous arterial spin labeling

PurposeTo implement and evaluate interleaved blip-up, blip-down, non-segmented 3D echo planar imaging (EPI) with pseudo-continuous arterial spin labeling (pCASL) and post-processing for reduced susceptibility artifact cerebral blood flow (CBF) maps.Materials and methods3D EPI non-segmented acquisition with a pCASL labeling sequence was modified to include alternating k-space coverage along phase encoding direction (referred to as “blip-reversed”) for alternating dynamic acquisitions of control and label pairs. Eight volunteers were imaged on a 3T scanner. Images were corrected for distortion using spatial shifting transformation of the underlying field map. CBF maps were calculated and compared with maps obtained without blip reversal using matching gray matter (GM) images from a high resolution 3D scan. Additional benefit of using the correction for alternating blip-up and blip-down acquisitions was assessed by comparing to corrected blip-up only and corrected blip-down only CBF maps. Matched Student t-test of overlapping voxels for the eight volunteers was done to ascertain statistical improvement in distortion.ResultsMean CBF value in GM for the eight volunteers from distortion corrected CBF maps was 50.8 ± 9.9 ml/min/100 gm tissue. Corrected CBF maps had 6.3% and 4.1% more voxels in GM when compared with uncorrected blip up (BU) and blip down (BD) images, respectively. Student t-test showed significant reduction in distortion when compared with blip-up images and blip-down images (p < 0.001). When compared with corrected BU and corrected BD only CBF maps, BU and BD corrected maps had 2.3% and 1% more voxels (p = 0.006 and 0.04, respectively).ConclusionPseudo-continuous arterial spin labeling with non-segmented 3D EPI acquisition using alternating blip-reversed k-space traversal and distortion correction provided significantly better matching GM CBF maps. In addition, employing alternating blip-reversed acquisitions during pCASL acquisition resulted in statistically significant improvement over corrected blip-up and blip-down CBF maps.     

Water and lipid diffusion MRI using chemical shift displacement-based separation of lipid tissue (SPLIT)

PurposeTo obtain water and lipid diffusion-weighted images (DWIs) simultaneously, we devised a novel method utilizing chemical shift displacement-based separation of lipid tissue (SPLIT) imaging.Materials and methodsSingle-shot diffusion echo-planar imaging without fat suppression was used and the imaging parameters were optimized to separate water and lipid DWIs by chemical shift displacement of the lipid signals along the phase-encoding direction. Using the optimized conditions, transverse DWIs at the maximum diameter of the right calf were scanned with multiple b-values in five healthy subjects. Then, apparent diffusion coefficients (ADCs) were calculated in the tibialis anterior muscle (TA), tibialis bone marrow (TB), and subcutaneous fat (SF), as well as restricted and perfusion-related diffusion coefficients (D and D*, respectively) and the fraction of the perfusion-related diffusion component (F) for TA.ResultsWater and lipid DWIs were separated adequately. The mean ADCs of the TA, TB, and SF were 1.56 ± 0.03 mm²/s, 0.01 ± 0.01 mm²/s, and 0.06 ± 0.02 mm²/s, respectively. The mean D*, D, and F of the TA were 13.7 ± 4.3 mm²/s, 1.48 ± 0.05 mm²/s, and 4.3 ± 1.6%, respectively.ConclusionSPLIT imaging makes it possible to simply and simultaneously obtain water and lipid DWIs without special pulse sequence and increases the amount of diffusion information of water and lipid tissue.     

Fast carotid artery MR angiography with compressed sensing based three-dimensional time-of-flight sequence

ObjectiveIn this study, we sought to investigate the feasibility of fast carotid artery MR angiography (MRA) by combining three-dimensional time-of-flight (3D TOF) with compressed sensing method (CS-3D TOF).Materials and methodsA pseudo-sequential phase encoding order was developed for CS-3D TOF to generate hyper-intense vessel and suppress background tissues in under-sampled 3D k-space. Seven healthy volunteers and one patient with carotid artery stenosis were recruited for this study. Five sequential CS-3D TOF scans were implemented at 1, 2, 3, 4 and 5-fold acceleration factors for carotid artery MRA. Blood signal-to-tissue ratio (BTR) values for fully-sampled and under-sampled acquisitions were calculated and compared in seven subjects. Blood area (BA) was measured and compared between fully sampled acquisition and each under-sampled one.ResultsThere were no significant differences between the fully-sampled dataset and each under-sampled in BTR comparisons (P > 0.05 for all comparisons). The carotid vessel BAs measured from the images of CS-3D TOF sequences with 2, 3, 4 and 5-fold acceleration scans were all highly correlated with that of the fully-sampled acquisition. The contrast between blood vessels and background tissues of the images at 2 to 5-fold acceleration is comparable to that of fully sampled images. The images at 2 × to 5 × exhibit the comparable lumen definition to the corresponding images at 1 ×.ConclusionBy combining the pseudo-sequential phase encoding order, CS reconstruction, and 3D TOF sequence, this technique provides excellent visualizations for carotid vessel and calcifications in a short scan time. It has the potential to be integrated into current multiple blood contrast imaging protocol.     

Bi-phase age-related brain gray matter magnetic resonance T1ρ relaxation time change in adults

ObjectivesTo investigate normative value and age-related change of brain magnetic resonance T1ρ relaxation at 1.5 T.MethodsThis study was approved by the local ethical committee with participants' written consent obtained. There were 42 adults healthy volunteers, including 20 males (age: 41 ± 16 (mean ± standard deviation) years, range: 22–68 years,) and 22 females (age: 39 ± 15 years, range: 21–62 years). MRI was performed at 1.5 T using 3D fluid suppressed turbo spin echo sequence. Regions-of-interests (ROIs) were obtained by atlas-based tissue segmentation and T1ρ was calculated by fitting the mean value to mono-exponential model. Correlation between T1ρ relaxation of brain gray matter regions and age was investigated.ResultsA regional difference among individual gray matter areas was noted; the highest values were observed in the hippocampus (98.37 ± 5.37 ms, median: 97.88 ms) and amygdala (94.95 ± 4.34 ms, median: 94.73 ms), while the lowest values were observed in the pallidum (83.81 ± 5.49 ms, median: 83.77 ms) and putamen (83.93 ± 4.76 ms, median: 83.99 ms). Gray matter T1ρ values decreased slowly (mean slope: − 0.256) and significantly (p < 0.05) with age in gray matter for subjects younger than 40 years old, while for subjects older than 40 years old there was no apparent correlation between T1ρ relaxation and age. Global white matter measured T1ρ value of 88.65 ± 3.47 ms (median: 87.86 ms), and the correlation with age was not significant (p = 0.18).ConclusionGray matter T1ρ relaxation demonstrates a bi-phase change with age in adults of 22–68 years.     

Assessment of cerebral blood perfusion reserve with acetazolamide using 3D spiral ASL MRI: Preliminary experience in pediatric patients

PurposeTo demonstrate the clinical feasibility of a new non-Cartesian cylindrically-distributed spiral 3D pseudo-continuous arterial spin labeling (pCASL) magnetic resonance imaging (MRI) pulse sequence in pediatric patients in quantifying cerebral blood flow (CBF) response to an acetazolamide (ACZ) vasodilator challenge.Materials and methodsMRI exams were performed on two 3 Tesla Philips Ingenia systems using 32 channel head coil arrays. After local institutional review board approval, the 3D spiral-based pCASL technique was added to a standard brain MRI exam and evaluated in 13 pediatric patients (average age: 11.7 ± 6.4 years, range: 1.4–22.2 years). All patients were administered ACZ for clinically indicated reasons. Quantitative whole-brain CBF measurements were computed pre- and post-ACZ to assess cerebrovascular reserve.Results3D spiral pCASL data were successfully reconstructed in all 13 cases. In 11 patients, CBF increased 2.8% to 93.2% after administration of ACZ. In the two remaining patients, CBF decreased by 2.4 to 6.0% after ACZ. The group average change in CBF due to ACZ was approximately 25.0% and individual changes were statistically significant (p < 0.01) in all patients using a paired t-test analysis. CBF perfusion data were diagnostically useful in supporting conventional MR angiography and clinical findings.Conclusion3D cylindrically-distributed spiral pCASL MRI provides a robust approach to assess cerebral blood flow and reserve in pediatric patients.     

MRI ductography of contrast agent distribution and leakage in normal mouse mammary ducts and ducts with in situ cancer

High resolution 3D MRI was used to study contrast agent distribution and leakage in normal mouse mammary glands and glands containing in situ cancer after intra-ductal injection. Five female FVB/N mice (~ 19 weeks old) with no detectable mammary cancer and eight C3(1) SV40 Tag virgin female mice (~ 15 weeks old) with extensive in situ cancer were studied. A 34G, 45° tip Hamilton needle with a 25μL Hamilton syringe was inserted into the tip of the nipple and approximately 15 μL of a Gadodiamide was injected slowly over 1 min into the nipple and throughout the duct on one side of the inguinal gland. Following injection, the mouse was placed in a 9.4 T MRI scanner, and a series of high resolution 3D T1-weighted images was acquired with a temporal resolution of 9.1 min to follow contrast agent leakage from the ducts. The first image was acquired at about 12 min after injection. Ductal enhancement regions detected in images acquired between 12 and 21 min after contrast agent injection was five times smaller in SV40 mouse mammary ducts (p < 0.001) than in non-cancerous FVB/N mouse mammary ducts, perhaps due to rapid washout of contrast agent from the SV40 ducts. The contrast agent washout rate measured between 12 min and 90 min after injection was ~ 20% faster (p < 0.004) in SV40 mammary ducts than in FVB/N mammary ducts. These results may be due to higher permeability of the SV40 ducts, likely due to the presence of in situ cancers. Therefore, increased permeability of ducts may indicate early stage breast cancers.