T1-weighted Fast Low-angle Shot Research Articles

The Direction of Flow and Phase-encoding Schemes Effects on Signal Intensity in T1-weighted Inversion Recovery TurboFLASH Images.

It is needed to minimize the effect of flow direction on the desired area, such as arterial input function (AIF) in magnetic resonance imaging (MRI). The current study aimed to investigate the effect of flow direction on different velocities (0-80.39 cm/s) for the strength of the signal intensity (SI) at the linear phase-encoding (LPE) and the center out phase-encoding (COPE) schemes and to recommend the best flow direction in a selected slice and scheme for absolute perfusion measurement by inversion recovery T1-weighted turbo fast low-angle shot (TurboFLASH) MR images. In this experimental study, the flow rates were measured using a flow phantom, and the signal intensity (SI) was measured at the two opposite flow directions in the Z-axis perpendicular to the coronal image at a concentration of 0.8 mmol/L of gadolinium-diethylenetriaminepantaacetic acid (Gd-DTPA) by using the LPE and COPE schemes. The increase in velocity along with the growth in SI and inflow affected the use of LPE and COPE acquisitions in both directions. The velocity of the arterial input function is needed to calculate the inflow correction factor by using two schemes in two opposite flow directions to investigate perfusion. The COPE scheme was better than the LPE scheme in measuring perfusion since the velocity and direction of blood flow affect SI less.

Automated segmentation of the locus coeruleus in aging and Alzheimer's disease using 3T neuromelanin-sensitive MRI.

The Locus Coeruleus (LC) may play an important role in the pathogenesis of Alzheimer's disease (AD). Neuromelanin-sensitive Magnetic Resonance Imaging (MRI) permits the visualization of the LC in vivo. Previously, we proposed an automatic, deep learning-based approach to segmenting the LC in a cohort of 82 healthy young and older adults (82 HC; Dünnwald et al. 2021). Here, we applied the same automatic segmentation method to baseline data from the DZNE Longitudinal Cognitive Impairment and Dementia (DELCODE) study comprising 42 healthy elderly adults (HEA), 18 participants with subjective cognitive decline (SCD), 25 participants with mild cognitive impairment (MCI) and 11 participants with AD. The LC was visualized using 3T T1-weighted Fast Low Angle Shot (FLASH) MRI acquired at 0.75mm isotropic resolution. Prior to processing, the data was sinc-interpolated to a resolution of 0.375mm³. The automated segmentation pipeline comprises two consecutive Convolutional Neural Networks (CNNs), which perform LC centerpoint regression and segmentation (see Fig. 1). The networks were trained only on the 82 HC dataset using a cross-validation scheme. We applied the networks to the unseen DELCODE data and assessed their performance with respect to manually delineated masks from two trained raters using Dice similarity coefficient (DSC) and intraclass correlation coefficient (ICC) of contrast ratios (CRs). In HEA, the networks showed similar agreement (DSC, ICC) compared to that observed between two independent raters. Using DSC, automated segmentation of SCD, MCI and AD groups showed less agreement than in the HEA group with 66.67%, 64.86%, 59.77% and 67.06% on average respectively (see Fig. 2). However, good reliability between automated and manually delineated masks for all groups using LC MRI contrast was observed (see Tab. 1) indicating that CRs may be relatively robust wrt. mask differences (see Fig. 3 and 4 for qualitative comparisons). The results demonstrate good reliability between manual and automatically generated LC segmentations with respect to LC MRI contrast using networks trained on healthy older adults. Additional fine-tuning of the networks to account for the variance in AD should be explored as a means to further improve reliability.

Fluid-based augmentation of magnetic resonance visualization of interventional devices.

PurposeTo evaluate the transient artifact augmentation of microtubes in magnetic resonance imaging by fluid injection.MethodsTwenty‐one fluorinated ethylene propylene catheters (inner diameter 760 μm) were filled with three different contrast media at various concentrations (Ferucarbotran, Resovist®, Bayer Schering Pharma; Manganese dichloride, MnCl2, Sigma‐Aldrich; Gadobutrol, Gadovist®, Bayer Schering Pharma). Artifact appearance was determined in an ex vivo phantom at 1.5 T using three different sequences: T1‐weighted three‐dimensional volume interpolated breath‐hold examination, T2‐weighted turbo spin echo, and T1‐weighted fast low angle shot. Catheter angulation to the main magnetic field (B0) was varied. Influence of parameters on artifact diameters was assessed with a multiple linear regression similar to an analysis of variance.ResultsArtifact diameter was significantly influenced by the contrast agent (p < 0.001), concentration of the contrast agent (p < 0.001), angulation of the phantom to B0 with the largest artifact at 90° (p < 0.001), and encoding direction with a larger diameter in phase encoding direction (PED, p < 0.001). Mean artifact diameters at 90° angulation to B0 in PED were 18.5 ± 5.4 mm in 0.5 mmol/ml Ferucarbotran, 8.7 ± 2.5 mm in 1 mmol/ml Gadobutrol, and 11.6 ± 4.6 mm in 5 mmol/ml MnCl2.ConclusionsFluid‐based contrast agents might be applied to interventional devices and thus temporarily augment the artifact ensuring both visibility and safe navigation.

In vivo quantification of the locus coeruleus and substantia nigra in parkinson's disease

Objectives: Locus coeruleus (LC) pathology in Parkinson's disease (PD) precedes and may be of even greater magnitude than that in the substantia nigra (SN). Novel magnetic resonance imaging (MRI) techniques now provide an opportunity to visualise and quantify LC degeneration in vivo. In this study we used in vivo T1-weighted Fast Low Angle Shot (FLASH) imaging to assess changes in LC volume and MRI contrast with respect to the SN in idiopathic PD and assessed the relationship to motor and non-motor symptoms.

Applicability of 3.0T MRI images in the estimation of full age based on shoulder joint ossification: Single-centre study.

Skeletal maturity is evaluated by many radiological methods for forensic age estimation. Direct radiography and computed tomography lead to a rise in ethical concerns due to radiation exposure. Therefore, magnetic resonance imaging (MRI) has currently been used in recent studies. In this study, the ossification stage of the shoulder joint was determined retrospectively in 178 male and 109 female individuals in the age group 12 to 30years using 3.0T MRI. All the images were evaluated with T1-weighted turbo spin echo (T1 TSE) sequence and T1 fast low angle shot two-dimensional sequence (T1 FL2D). The combined staging method, which was defined by Kellinghaus et al. and Schmeling et al., was used. The intra- and inter-observer agreement levels were very good (κ and κw). There were no significant age differences between males and females in all stages. In most of the stages, the ossification of the proximal humeral epiphyses occurred earlier in females than in males. Stage 4 did not occur in either of the sexes before the 18th birthday as the youngest patients in this stage was at 19 and 18years of age in males and females, respectively. We concluded that evaluating the ossification of the proximal humeral epiphysis with MRI imaging for forensic age estimation may be beneficial. Evaluating the same anatomical structure with different MRI sequences may be useful for accurate staging diagnosis.

Artefact and ablation performance of an MR-conditional high-power microwave system in bovine livers: an exvivo study

BackgroundWe evaluated a magnetic resonance (MR)-conditional high-power microwave ablation system.MethodsAn exvivo 1.5-T evaluation was conducted by varying the sequence (T1-weighted volume interpolated breath-hold examination, T1w-VIBE; T1-weighted fast low-angle shot, T1w-FLASH; T2-weighted turbo spin-echo, T2w-TSE), applicator angulation to B0 (A-to-B0), slice orientation, and encoding direction. Tip location error (TLE) and artefact diameters were measured, and influence of imaging parameters was assessed with analysis of variance and post hoc testing. Twenty-four exvivo ablations were conducted in three bovine livers at 80 W and 120 W. Ablation durations were 5, 10, and 15 min. Ablation zones were compared for short-axis diameter (SAD), volume, and sphericity index (SI) with unpaired t test.ResultsThe artefact pattern was similar for all sequences. The shaft artefact (4.4 ± 2.9 mm, mean ± standard deviation) was dependent on the sequence (p = 0.012) and the A-to-B0 (p < 0.001); the largest shaft diameter was measured with T1w-FLASH (6.3 ± 3.4 mm) and with perpendicular A-to-B0 (6.7 ± 2.4 mm). The tip artefact (1.6 ± 0.7 mm) was dependent on A-to-B0 (p = 0.001); TLE was -2.6 ± 1.0 mm. Ablation results at the maximum setting (15 min, 120 W) were SAD = 42.0 ± 1.41 mm; volume = 56.78 ± 3.08 cm3, SI = 0.68 ± 0.05. In all ablations, SI ranged 0.68–0.75 with the smallest SI at 15 min and 120 W (p = 0.048).ConclusionThe system produced sufficiently large ablation zones and the artefact was appropriate for MR-guided interventions.

Locus coeruleus MRI contrast is reduced in Alzheimer's disease dementia and correlates with CSF Aβ levels

IntroductionThis study aimed to assess how interindividual differences in locus coeruleus (LC) magnetic resonance imaging (MRI) contrast relate to cerebrospinal fluid (CSF) biomarkers of Alzheimer's disease (AD). MethodsLC MRI contrast was quantified in 73 individuals from the DZNE Longitudinal Cognitive Impairment and Dementia Study (DELCODE) study comprising 25 healthy elderly adults and 21 individuals with subjective cognitive decline, 16 with mild cognitive impairment, and 11 participants with AD dementia using 3D T1-weighted fast low-angle shot (FLASH) imaging (0.75 mm isotropic resolution). Bootstrapped Pearson's correlations between LC contrast, CSF amyloid, and tau were performed in 44 individuals with CSF biomarker status. ResultsA significant regional decrease in LC MRI contrast was observed in patients with AD dementia but not mild cognitive impairment and subjective cognitive decline compared with healthy controls. A negative association between LC MRI contrast and levels of CSF amyloid but not with CSF tau was found. DiscussionThese results provide first evidence for a direct association between LC MRI contrast using in vivo T1-weighted FLASH imaging and AD pathology.

Optimal Conditions for 3D Non-contrast T1-weighted Magnetic Resonance Imaging Segmented Turbo Fast Low-angle Shot for Tissue Characterization of Coronary Plaques

In three-dimensional (3D) T1-weighted magnetic resonance imaging used for tissue characterization of coronary plaques, the contrast for electrocardiographic synchronization may vary according to the R-R interval (RR). The coronary artery plaque image shows suppression of the fluid compartment signal for the coronary artery luminal blood as well as the fat signal in the region of interest; in addition, it is necessary to ensure that the value of the plaque-to-muscle signal intensity ratio (PMR) does not change according to the difference in RR. In the current study, the phantom review and clinical data suggested that the PMR changes that occur due to the differences in RR can be minimized by adjusting the inversion time (TI) in the range of the required black blood effect. Moreover, the signal-to-noise ratio (SNR), which varies according to the difference between the RR and the TI, was determined to identify the maximum value flip angle (FA) value that would lead to improvement in the SNR. Thus, signal suppression of the PMR, SNR, and the fluid compartment of the coronary artery luminal blood can be controlled using different RRs with the relational expressions for calculating optimal TI and FA.

In vivo MRI assessment of the human locus coeruleus along its rostrocaudal extent in young and older adults

The locus coeruleus (LC), a major origin of noradrenergic projections in the central nervous system (CNS), may serve a critical role in the pathogenesis of neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). As such, there is considerable interest to develop magnetic resonance imaging (MRI) techniques to assess the integrity of the LC in vivo. The high neuromelanin content of the LC serves as an endogenous contrast for MRI but existing protocols suffer from low spatial resolution along the rostrocaudal axis of the LC rendering it difficult to differentiate its integrity in caudal and rostral portions. This study presents a novel approach to investigate the human LC in vivo using T1-weighted Fast Low Angle Shot (FLASH) MRI at 3 T (T). Using high-resolution isotropic imaging to minimise the effect of low spatial resolution in the slice direction, this study aimed to characterise the rostrocaudal distribution of LC signal intensity attributed to neuromelanin from 25 young (22–30) and 57 older (61–80) adults. We found a significant age-related increase in maximum but not median signal intensity, indicating age-related differences were not homogenous. Instead, they were confined to the rostral third of the LC with relative sparing of the caudal portion. The findings presented demonstrate in vivo T1-weighted FLASH imaging may be used to characterise signal intensity changes across the entire rostrocaudal length of the LC (a corresponding standardised LC map is available for download), which may help to identify how the human LC is differentially affected in aging and neurodegenerative disease.

Diagnostic accuracy of different magnetic resonance imaging sequences for detecting local tumor progression after radiofrequency ablation of hepatic malignancies

ObjectiveTo evaluate the diagnostic accuracy of the individual sequences of a clinical routine liver MRI protocol for the detection of local tumour progression after radiofrequency (RF) ablation of hepatic malignancies. Material and methodsA cohort of 93 patients treated for 140 primary and secondary hepatic malignancies with RF ablation was assembled for this retrospective study. The cohort contained 31 cases of local tumour progression, which occurred 8.3±6.2months (range: 4.0–28.2 months) after treatment. All patients underwent clinical routine follow-up MRI at 1.5T including following sequences: unenhanced T1-weighted fast low angle shot (FLASH-2D), T2-weighted turbo-spin-echo sequence, contrast-enhanced (CE) T1-weighted volume-interpolated breath-hold examination (VIBE), diffusion-weighted imaging (DWI). Follow-up was 32.7±22.5months (range: 4.0–138.3 months). Two readers independently evaluated the individual sequences separately for signs of local tumour progression. Diagnostic confidence was rated on a 4-point scale. Inter-reader agreement was assessed with Coheńs kappa. Long-term follow-up and histological specimen served as standard of reference. ResultsBoth readers reached the highest sensitivity for detection of local tumour progression with unenhanced T1-FLASH 2D (88.2% and 94.1%, respectively) and the highest specificity with CE T1-VIBE (96.2% and 97.2%, respectively). Highest inter-reader agreement was reached with T1-FLASH-2D (kappa=0.83). Typical pitfalls for false-positive diagnoses were focal cholestasis and vasculature adjacent to the ablation zone. Diagnostic confidence was highest with CE T1-VIBE for reader 1 and DWI for reader 2. ConclusionUnenhanced T1-FLASH-2D is an essential sequence for follow-up imaging after tumour ablation with a high sensitivity for detection of local progression and a high inter-reader agreement.

Safety of externally stimulated intracranial electrodes during functional MRI at 1.5 T

Surgical resection of the epileptogenic zone (EZ) is a potential cure for medically refractory focal epilepsy. Proper identification of the EZ is essential for such resection. Synergistic application of functional magnetic resonance imaging (fMRI) simultaneously with stimulation of a single externalized intracranial stereotactic EEG (SEEG) electrode has the potential to improve identification of the EZ. While most EEG-fMRI studies use the electrodes passively to record electrical activity, it is possible to stimulate the brain using the electrodes by connecting them with conducting cables to the stimulation hardware. In this study, we investigated the effect of MRI-induced heating on a single SEEG electrode and its sensitivity to geometry, configuration, and associated connections required for the stimulation. The temperature increase of a single electrode embedded within a gel phantom and connected to an external stimulation system was measured during 1.5T MRI scans using adjacent fluoroptic temperature sensors. A receive-only split-array head coil and a transmit-receive head coil were used for testing. Sequences included a standard localizer, T1-weighted axial fast low-angle shot (FLASH), gradient echo-planar imaging (GE-EPI) axial fMRI, and a high specific absorption rate T2-weighted turbo spin-echo (TSE) axial scan. Variations of the electrode location and connecting cable configuration were tested. No unacceptable heating was observed with the standard sequences used for evaluation of the EZ. Considerable heating (up to 14°C) was observed with the TSE sequence, which is not used clinically. The temperature increase was insignificant (<0.05°C) for electrode contacts closest to the isocenter and connecting cables lying along the isocenter, and varied with configurations of the connecting cable assembly. Simultaneous intracranial electrode stimulation during fMRI using an externalized stimulation system may be safe with strict adherence to settings tested prior to the fMRI. Localizer, FLASH, and GE-EPI fMRI may be safely performed in patients with a single SEEG electrode following the configurations tested in this study, but high SAR TSE scans should not be performed in these patients.

50. Magnetic Resonance Imaging optimization for liver SBRT: Breath-triggered acquisition in treatment position to improve lesion contouring

Introduction Magnetic Resonance Imaging (MRI) acquisition in treatment position was implemented in our institution for the need of stereotactic body radiotherapy (SBRT) program. During imaging acquisition, significant liver motion is usually observed due to breathing motion. The aim of this study is to report the benefits of setting out a breath-triggered MRI protocol optimized for radiotherapy (RT) planning in order to account for liver motion. Material and methods Prior to imaging, three internal gold fiducials were implanted under echo or CT guidance in the vicinity of the lesion site in order to improve images registration, patient’s positioning and target volume tracking during SBRT treatment. A 4D CT scan was acquired in treatment position. Images were reconstructed in six phases across the respiratory cycle with CT50 being the exhale image set used for MR image registration. MRI was acquired with a 18-channel design body ex coil on a 1.5T MR scan. The patients were set up with the same immobilization and positioning devices as for CT imaging thanks to a MR compatible table. The three sequences were systematically used:- For lesion visualization, axial single shot fast spin echo T2-weighted (T2) with fat saturation was first acquired with breath triggering on exhale. – Fiducials are visible on ultra-fast gradient echo T1-weighted DIXON (T1 DIXON) water reconstructed images acquired in exhale breath hold. – Lesion are also well defined after injected T1-weighted Fast Low Angle Shot (T1 TFL) imaging sequence acquired with breath triggering on expiration phase. Gold fiducials are also visible on this sequence. Slice thickness was set to 2 mm and all sequences were acquired in the same plane with the same slice position in order to ease image registration in the treatment planning software. The entire MRI protocol acquisition lasts around 20 min depending on the regularity of the patient’s breathing pattern. Results The lesion was not always visible on 4D CT scan, even on images with contrast enhancement hence the need of MRI to better define the lesion. Target motion range was assessed based on fiducials’ displacement. Most frequently, treatment planning is performed on expiration phases but when lesion movement is small with breathing, target contouring is done over all phases and treatment planning is achieved in free breathing. The use of the same table and immobilization device for MRI minimized uncertainties due to patient position for image registration. An example of MR/CT50 registration and target volume definition is illustrated on Fig. 1. Download : Download high-res image (447KB) Download : Download full-size image Conclusion The use of MR imaging sequences optimized to account for fiducial visualization and tumor delineation allow high precision target delineation for treatment planning. Increasing cases of patients eligible for SBRT and its proof of benefit have stimulated the effort to setup and improve new imaging protocols at our institute for a personalized and optimal SBRT treatment. Recent developments in 4D MRI demonstrated the possibility to sort and reconstruct the images according to the respiratory phases [1] , [2] , [3] . Future implementation of 4D MRI in our institution would allow better registration with 4D CT planning over the entire breathing cycle and delineation accuracy will benefit from significant improvements.

In vitro artefact assessment of a new MR-compatible microwave antenna and a standard MR-compatible radiofrequency ablation electrode for tumour ablation.

To evaluate and compare artefact configuration and diameters in a magnetic resonance (MR)-compatible prototype microwave (MW) applicator and a standard MR-compatible radiofrequency (RF) applicator for MR-guided tumour ablation. Both applicators were tested in a phantom study at 1.5T with three sequences: T1-weighted three-dimensional volume interpolated breath-hold examination (VIBE), T1-weighted fast low angle shot (FLASH), T2-weighted turbo spin echo (TSE). Applicator orientation to main magnetic field (B0) and slice orientation were varied. Needle tip location error (TLE) was assessed, and artefact diameters were calculated. Influence of imaging parameters on artefacts was assessed with analysis of variance (ANOVA) and post hoc testing. MW applicator: the shaft artefact diameter measured 2.3 +/- 0.8 mm. Tip artefact diameter and length measured 2.2 ± 0.8 mm and 2.4 ± 1.3 mm, respectively. A prominent oval artefact (diameter: 16.5 +/- 1.8 mm, length: 19.1 +/- 2.5 mm) appeared close to the tip. TLE: - .3 +/- 0.6 mm. RF applicator: shaft and tip diameter measured 8.9 +/- 4.7 mm and 9.0 +/- .0 mm, respectively. TLE: -0.1 +/- 0.8 mm. Minimal artefacts were measured with RF applicator orientation parallel to B0 (P < 0.0001), whereas no such influence was found for MW applicator. For both applicators, significantly large artefacts were measured with T1 FLASH (P = 0.03). The MW applicator's artefact is satisfactory and seems useable for MR-guided ablation procedures. MW applicator's artefact appearance is independent of angulation to main magnetic field. MW applicator's prominent distal artefact may increase visibility under MR-guidance. RF and MW applicator's artefacts are precise concerning tip depiction. Largest artefact diameters are measured with T1-weighted fast low angle shot sequence.

Detection of small brain metastases at 3 T: comparing the diagnostic performances of contrast-enhanced T1-weighted SPACE, MPRAGE, and 2D FLASH imaging

The aim of this study was to compare the diagnostic performance of contrast-enhanced T1-weighted sampling perfection with application-optimized contrasts using different flip angle evolutions (SPACE), magnetization-prepared rapid gradient-echo (MPRAGE), and two-dimensional (2D) fast low angle shot (FLASH) for the detection of small brain metastases.Twelve patients who had brain metastases less than 10 mm in diameter were enrolled. The diagnostic performance was evaluated using alternative free-response receiver operating characteristic analysis. Sensitivity and positive predictive value were also calculated.The mean Az and sensitivities of SPACE for all observers were significantly higher than those of MPRAGE and 2D FLASH.

Non-uniformity of Clinical Head, Head and Neck, and Body Coils in Magnetic Resonance Imaging (MRI)

Introduction Signal intensity uniformity in a magnetic resonance (MR) image indicates how well the MR imaging (MRI) system represents an object. One of the major sources of image non-uniformity in high-field MRI scanners is inhomogeneity of radio-frequency coil. The aim of this study was to investigate non-uniformity in head, head and neck, and body coils and compare the obtained results to determine the best clinical coil for future clinical application. Materials and Methods A phantom was designed to investigate the non-uniformity of coils. All evaluations were carried out using a 1.5 T clinical MRI scanner. T1-weighted inversion recovery sequence (linear phase encoding) and turbo fast low angle shot (TurboFLASH) images were used to find non-uniformity in the clinical coils. For testing the uniformity of coils, signal intensity profiles in parts of the coronal image of phantom were measured over X and Y axes. Results The results showed that body coil was the most uniform coil of all; in addition, the head and neck coil was more uniform than the head coil. The results also indicated that signal-to-noise ratio (SNR) of the head and neck coil was higher than the head and body coils. Moreover, SNR of the head coil was higher than that of the body coil. Conclusion In order to accurately find or apply an image signal intensity for measuring organ blood flow or perfusion, coil non-uniformity corrections are required.

Detection of lung tumors in mice using a 1-tesla compact magnetic resonance imaging system.

Due to their small size, lung tumors in rodents are typically investigated using high-field magnetic resonance (MR) systems (4.7 T or higher) to achieve higher signal-to-noise ratios, although low-field MR systems are less sensitive to susceptibility artifacts caused by air in the lung. We investigated the feasibility of detecting lung tumors in living, freely breathing mice with a 1-T compact permanent magnet MR system. In total, 4 mice were used, and MR images of mouse lungs were acquired using a T1-weighted three-dimensional fast low-angle shot sequence without cardiac or respiratory gating. The delineation and size of lung tumors were assessed and compared with histopathological findings. Submillimeter lesions were demonstrated as hyperintense, relative to the surrounding lung parenchyma, and were delineated clearly. Among the 13 lesions validated in histopathological sections, 11 were detected in MR images; the MR detection rate was thus 84.6%. A strong correlation was obtained in size measurements between MR images and histological sections. Thus, a dedicated low-field MR system can be used to detect lung tumors in living mice noninvasively without gating.

MRI of the hip at 7T: Feasibility of bone microarchitecture, high-resolution cartilage, and clinical imaging

To demonstrate the feasibility of performing bone microarchitecture, high-resolution cartilage, and clinical imaging of the hip at 7T. This study had Institutional Review Board approval. Using an 8-channel coil constructed in-house, we imaged the hips of 15 subjects on a 7T magnetic resonance imaging (MRI) scanner. We applied: 1) a T1-weighted 3D fast low angle shot (3D FLASH) sequence (0.23 × 0.23 × 1-1.5 mm(3) ) for bone microarchitecture imaging; 2) T1-weighted 3D FLASH (water excitation) and volumetric interpolated breath-hold examination (VIBE) sequences (0.23 × 0.23 × 1.5 mm(3) ) with saturation or inversion recovery-based fat suppression for cartilage imaging; 3) 2D intermediate-weighted fast spin-echo (FSE) sequences without and with fat saturation (0.27 × 0.27 × 2 mm) for clinical imaging. Bone microarchitecture images allowed visualization of individual trabeculae within the proximal femur. Cartilage was well visualized and fat was well suppressed on FLASH and VIBE sequences. FSE sequences allowed visualization of cartilage, the labrum (including cartilage and labral pathology), joint capsule, and tendons. This is the first study to demonstrate the feasibility of performing a clinically comprehensive hip MRI protocol at 7T, including high-resolution imaging of bone microarchitecture and cartilage, as well as clinical imaging.

Nonenhanced Magnetic Resonance Angiography of the Lower Extremity Vessels at 7 Tesla

The aim of this study was to investigate the feasibility of nonenhanced magnetic resonance angiography (MRA) of the lower extremities at 7 tesla (T). Eight healthy volunteers were examined on a 7-T whole-body magnetic resonance system. For image acquisition, a custom-built 16-channel transmit/receive coil and a manually positionable AngioSURF table for multistation imaging were used. A nonenhanced T1-weighted 2-dimensional fast low-angle shot (2D FLASH) sequence was acquired with and without venous saturation radiofrequency pulses in axial orientation, covering the vasculature from the pelvis to the feet. Acquisition time of 1 table position amounted to 2 minutes and 19 seconds (with venous saturation pulse) and 1 minute and 9 seconds (without venous saturation pulse), covering a field of view of approximately 10 cm in the z-axis. Time-interleaved acquisition of modes was integrated to obtain homogeneous image quality of the vasculature. A qualitative image analysis was performed in the iliac, femoral, popliteal, and tibiofibular vessel segments regarding vessel delineation using a 5-point scale (5 to 1, excellent vessel delineation to nondiagnostic). For the quantitative image evaluation, the signal was measured in the specified segments and in the surrounding musculature of both legs to obtain contrast ratios (CR). T1-weighted 2D FLASH imaging enabled homogeneous, hyperintense delineation of the arteries with saturation of surrounding tissue in almost all analyzed vessel segments. The qualitative image evaluation demonstrated a moderate to good delineation and assessment of the vessel lumen (mean score: iliac, 3.17; femoral, 3.71; popliteal, 4.00; and tibiofibular, 3.31 for 2D FLASH). The quantitative analysis showed similar CRs in all vessel segments, with the best contrast to surrounding tissue achieved in the femoral segments (CRiliac, 0.59; CRfemoral, 0.69; CRpopliteal, 0.74; and CRtibiofibular, 0.57), although a medial signal drop-off in the thigh region could be found in some volunteers. Transformation of the axial images into coronal maximum intensity projection images revealed an artifact characterized by recurrent short declines of vessel signal, most probably because of an interference between the alternating pressure and flow effects during systole and diastole and the image acquisition frequency. Nevertheless, the use of time-interleaved acquisition of modes enabled a homogenous image quality with successful reduction of B1 field inhomogeneities. The results of our study demonstrate the feasibility of non-contrast-agent-enhanced MRA of the lower extremity vessels at 7 T. Nonenhanced MRA of the lower extremities at this very high magnetic field can be considered to be in an early but promising stage. Further sequence optimization and the examination of a larger number of participants as well as comparison with contrast-enhanced MRA and nonenhanced techniques at lower field strengths should be pursued in future trials.

Study of surgical indication for knee arthroplasty by cartilage analysis in three compartments using data from Osteoarthritis Initiative (OAI)

BackgroundBicompartmental or unicompartmental knee arthroplasty (BKA, UKA) is currently advocated as an alternative solution to conventional total knee arthroplasty (TKA) in order to preserve bone stock and ligaments for limited osteoarthritis (OA) with intact anterior and posterior cruciate ligaments (ACL, PCL). However, the actual rate of UKA or BKA compared to TKA procedures in OA patients has not been reported. In this study, we retrospectively analyzed preoperative MRI of the knee in subjects who underwent knee arthroplasty and assessed the potential for UKA or BKA as an alternative treatment.MethodsData were extracted from the Osteoarthritis Initiative (OAI) public use data set, which included 4,796 subjects, ages 45–79. 3.0 Tesla MRI scanners were dedicated to imaging the knees of OAI participants annually from February 2004 to March 2010. Extensive quantitative measurements of the knee MRI were performed on 87 patients who underwent knee arthroplasty during follow-up visits. We assessed the cartilage thickness and defect size in the medial femorotibial joint (FTJ), lateral FTJ, and patellofemoral joint (PFJ) as well as ligamentous injury, bone marrow edema, and subchondral cyst size from 2D coronal turbo spin echo (TSE), 2D sagittal TSE, 3D coronal T1-weighted water-excitation fast low angle shot (FLASH), and 3D sagittal water-excitation double echo steady-state (DESS) with axial and coronal reformat images.ResultsEighty-five subjects (97.7%) were subjected to TKA, while only 2 subjects (2.3%) received UKA from the OAI database. Based on the preoperative MRI findings criteria, 51 of 87 subjects (58.6%) met the indication for TKA including the 2 UKA subjects above. This rate was significantly lower (p<0.001) than the actual TKA rate received. Among 85 subjects who actually underwent TKA, 31 subjects (36.5%) and 5 subjects (5.9%) met the indication for BKA and UKA, respectively.ConclusionsMany medial or lateral compartmental OA subjects, with or without patellar compartment defects have undergone TKA. The results of this study suggest the indication for partial arthroplasty, such as UKA or BKA, may increase when cartilage in each compartment, as well as ligaments and subchondral bone status are comprehensively evaluated.

Classification of Coronary Atherosclerotic Plaques Ex Vivo With T1, T2, and Ultrashort Echo Time CMR

This study sought to determine whether the classification of human coronary atherosclerotic plaques with T1, T2, and ultrashort echo time (UTE) cardiac magnetic resonance (CMR) would correlate well with atherosclerotic plaque classification by histology. CMR has been extensively used to classify carotid plaque, but its ability to characterize coronary plaque remains unknown. In addition, the detection of plaque calcification by CMR remains challenging. Here, we used T1, T2, and UTE CMR to evaluate atherosclerotic plaques in fixed post-mortem human coronary arteries. We hypothesized that the combination of T1, T2, and UTE CMR would allow both calcified and lipid-rich coronary plaques to be accurately detected. Twenty-eight plaques from human donor hearts with proven coronary artery disease were imaged at 9.4-T with a T1-weighted 3-dimensional fast low-angle shot (FLASH) sequence (250-μm resolution), a T2-weighted rapid acquisition with refocused echoes (RARE) sequence (in-plane resolution 0.156 mm), and an UTE sequence (300-μm resolution). Plaques showing selective hypointensity on T2-weighted CMR were classified as lipid-rich. Areas of hypointensity on the T1-weighted images, but not the UTE images, were classified as calcified. Hyperintensity on the T1-weighted and UTE images was classified as hemorrhage. Following CMR, histological characterization of the plaques was performed with a pentachrome stain and established American Heart Association criteria. CMR showed high sensitivity and specificity for the detection of calcification (100% and 90%, respectively) and lipid-rich necrotic cores (90% and 75%, respectively). Only 2 lipid-rich foci were missed by CMR, both of which were extremely small. Overall, CMR-based classification of plaque was in complete agreement with the histological classification in 22 of 28 cases (weighted κ = 0.6945, p < 0.0001). The utilization of UTE CMR allows plaque calcification in the coronary arteries to be robustly detected. High-resolution CMR with T1, T2, and UTE contrast enables accurate classification of human coronary atherosclerotic plaque.