HASTE sequence with parallel acquisition and T2 decay compensation: application to carotid artery imaging

Advanced MRI techniques in abdominal imaging

Magnetic resonance imaging (MRI) is a crucial modality for abdominal imaging evaluation of focal lesions and tissue properties. However, several obstacles, such as prolonged scan times, limitations in patients' breath-hold capacity, and contrast agent-associated artifacts, remain in abdominal MR images. Recent techniques, including parallel imaging, three-dimensional acquisition, compressed sensing, and deep learning, have been developed to reduce the scan time while ensuring acceptable image quality or to achieve higher resolution without extending the scan duration. Quantitative measurements using MRI techniques enable the noninvasive evaluation of specific materials. A comprehensive understanding of these advanced techniques is essential for accurate interpretation of MRI sequences. Herein, we therefore review advanced abdominal MRI techniques.

Comprehensive review of artifacts in cardiac MRI and their mitigation

Cardiac magnetic resonance imaging (CMR) is an important clinical tool that obtains high-quality images for assessment of cardiac morphology, function, and tissue characteristics. However, the technique may be prone to artifacts that may limit the diagnostic interpretation of images. This article reviews common artifacts which may appear in CMR exams by describing their appearance, the challenges they mitigate true pathology, and offering possible solutions to reduce their impact. Additionally, this article acts as an update to previous CMR artifacts reports by including discussion about new CMR innovations.

Analysis of blurring due to short T2 decay at different resolutions in 23Na MRI

The nuclear magnetic resonance signal from sodium (23Na) nuclei demonstrates a fast bi-exponential T2 decay in biological tissues (T2,short = 0.5-5 ms and T2,long = 10-30 ms). Hence, blurring observed in sodium images acquired with center-out sequences is generally assumed to be dominated by signal attenuation at higher k-space frequencies. Most of the studies in the field primarily focus on the impact of readout duration on blurring but neglect the impact of resolution. In this paper, we examine the blurring effect of short T2 on images at different resolutions. A series of simulations, as well as phantom and in vivo scans were performed at varying resolutions and readout durations in order to evaluate progressive changes in image quality. We demonstrate that, given a fixed readout duration, T2 decay produces distinct blurring effects at different resolutions. Therefore, in addition to voxel size-dependent partial volume effects, the choice of resolution adds additional T2-dependent blurring.

Free-breathing accelerated whole-body MRI using an automated workflow: Comparison with conventional breath-hold sequences

Whole-body magnetic resonance imaging (MRI) has become increasingly popular in oncology. However, the long acquisition time might hamper its widespread application. We sought to assess and compare free-breathing sequences with conventional breath-hold examinations in whole-body MRI using an automated workflow process. This prospective study consisted of 20 volunteers and six patients with a variety of pathologies who had undergone whole-body 1.5-T MRI that included T1-weighted radial and Dixon volumetric interpolated breath-hold examination sequences. Free-breathing sequences were operated by using an automated user interface. Image quality, diagnostic confidence, and image noise were evaluated by two experienced radiologists. Additionally, signal-to-noise ratio was measured. Diagnostic performance for the overall detection of pathologies was assessed using the area under the receiver operating characteristics curve (AUC). Study participants were asked to rate their examination experiences in a satisfaction survey. MR free-breathing scans were rated as at least equivalent to conventional MR scans in more than 92% of cases, showing high overall diagnostic accuracy (95% [95% CI 92-100]) and performance (AUC 0.971, 95% CI 0.942-0.988; p < 0.0001) for the assessment of pathologies at simultaneously reduced examination times (25 ± 2 vs. 32 ± 3 min; p < 0.0001). Interrater agreement was excellent for both free-breathing (ϰ = 0.96 [95% CI 0.88-1.00]) and conventional scans (ϰ = 0.93 [95% CI 0.84-1.00]). Qualitative and quantitative assessment for image quality, image noise, and diagnostic confidence did not differ between the two types of MR image acquisition (all p > 0.05). Scores for patient satisfaction were significantly better for free-breathing compared with breath-hold examinations (p = 0.0145), including significant correlations for the grade of noise (r = 0.79, p < 0.0001), tightness (r = 0.71, p < 0.0001), and physical fatigue (r = 0.52, p = 0.0065). In summary, free-breathing whole-body MRI in tandem with an automated user interface yielded similar diagnostic performance at equivalent image quality and shorter acquisition times compared to conventional breath-hold sequences.

Comprehensive Clinical Evaluation of a Deep Learning-Accelerated, Single-Breath-Hold Abdominal HASTE at 1.5 T and 3 T

To evaluate the clinical performance of a deep learning-accelerated single-breath-hold half-Fourier acquisition single-shot turbo spin echo (HASTE_DL)-sequence for T2-weighted fat-suppressed MRI of the abdomen at 1.5 T and 3 T in comparison to standard T2-weighted fat-suppressed multi-shot turbo spin echo-sequence. A total of 320 patients who underwent a clinically indicated liver MRI at 1.5 T and 3 T between August 2020 and February 2021 were enrolled in this single-center, retrospective study. HASTE_DL and standard sequences were assessed regarding overall and organ-based image quality, noise, contrast, sharpness, artifacts, diagnostic confidence, as well as lesion detectability using a Likert scale ranging from 1 to 4 (4 = best). The number of visible lesions of each organ was counted and the largest diameter of the major lesion was measured. HASTE_DL showed excellent image quality (median 4, interquartile range 3-4), although BLADE (median 4, interquartile range 4-4) was rated significantly higher for overall and organ-based image quality of the adrenal gland (P < .001), contrast (P < 0.001), sharpness (P < 0.001), artifacts (P < 0.001), as well as diagnostic confidence (P < .001). No significant differences were found concerning noise (P = 0.886), organ-based image quality of the liver, pancreas, spleen, and kidneys (P = 0.120-0.366), number and measured diameter of the detected lesions (ICC = 0.972-1.0). Reduction of the aquisition time (TA) was at least 89% for 1.5 T images and 86% for 3 T images. HASTE_DL provided excellent image quality, good diagnostic confidence and lesion detection compared to a standard T2-sequences, allowing an eminent reduction of the acquisition time.

Lung MRI to predict response or lack of response to treatment in interstitial lung disease: initial observations on SSFSE/PROPELLER T2 match/mismatch

BACKGROUND

Ground-glass opacities (GGO) are frequently found in interstitial lung diseases (ILD) and may represent either active inflammation or subresolution interstitial fibrosis. We sought to investigate the ability of lung MRI to predict treatment response in individuals with ILD presenting with predominant GGO. Methods: prospective cohort, 15 participants presenting with ILD manifested as predominant GGO and referred for a new treatment regimen with a systemic glucocorticoid and/or an immunosuppressive agent, underwent 1.5 T lung MRI. SSFSE/PROPELLER T2 mismatch sign, relative signal intensity on T2-weighted images and relative enhancement of lung lesions were compared to functional response, defined as a greater than 10% increase in forced vital capacity in 10 weeks (primary endpoint).

RESULTS

SSFSE/PROPELLER T2 match/mismatch was able to discriminate responders from nonresponders for the primary endpoint in 12 of 15 participants (80% accuracy, p = 0.026) for readers 1 and 2, and in 13 of 15 participants (87% accuracy, p = 0.011) for reader 3, with interrater agreement of 87% between readers 1 and 2 (Cohen's kappa coefficient of 0.732) and 93% between readers 1/2 and 3 (Cohen's kappa coefficient of 0.865).

CONCLUSIONS

SSFSE-PROPELLER T2 match/mismatch was predictive of treatment response status in this group of ILD patients. Abbreviations FVC: forced vital capacityGGO; ground-glass opacities; HRCT: High-Resolution Computed Tomography; ILD: interstitial lung disease; LAVA: Liver Acquisition with Volume Acceleration; mMRC: modified Medical Research Council dyspnea score; MRI: Magnetic Resonance Image; PROPELLER: Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction; SI: signal intensity; SSFSE: Single-Shot Fast Spin Echo.

Optimization of pulse sequences in ultrafast magnetic resonance imaging for the diagnosis of acute abdominal pain caused by gastrointestinal disease

Background

Magnetic resonance imaging (MRI) is widely used to diagnose acute abdominal pain; however, it remains unclear which pulse sequence has priority in acute abdominal pain.

Purpose

To investigate the diagnostic accuracy of MRI and to assess the conspicuity of each pulse sequence for the diagnosis of acute abdominal pain due to gastrointestinal diseases

Material and Methods

We retrospectively enrolled 60 patients with acute abdominal pain who underwent MRI for axial and coronal T2-weighted (T2W) imaging, fat-suppressed (FS)-T2W imaging, and true-fast imaging with steady-state precession (True-FISP) and axial T1-weighted (T1W) imaging and investigated the diagnosis with endoscopy, surgery, histopathology, computed tomography, and clinical follow-up as standard references. Two radiologists determined the diagnosis with MRI and rated scores of the respective sequences in assessing intraluminal, intramural, and extramural abnormality using a 5-point scale after one month. Diagnostic accuracy was calculated and scores were compared by Wilcoxon-signed rank test with Bonferroni correction.

Results

Diagnostic accuracy was 90.0% and 93.3% for readers 1 and 2, respectively. Regarding intraluminal abnormality, T2W, FS-T2W, and True-FISP imaging were superior to T1W imaging in both readers. FS-T2W imaging was superior to True-FISP in reader 2 (P < 0.0083). For intramural findings, there was no significant difference in reader 1, whereas T2W, FS-T2W, and True-FISP imaging were superior to T1W imaging in reader 2 (P < 0.0083). For extramural findings, FS-T2W imaging was superior to T2W, T1W, and True-FISP imaging in both readers (P < 0.0083).

Conclusion

T2W and FS-T2W imaging are pivotal pulse sequences and should be obtained before T1W and True-FISP imaging.

MR Imaging-based Evaluation of Mesenteric Ischemia Caused by Strangulated Small Bowel Obstruction and Mesenteric Venous Occlusion: An Experimental Study Using Rabbits

PURPOSE

This study assessed the MRI findings of strangulated small bowel obstruction (SBO) and mesenteric venous occlusion (MVO) in a rabbit model using 3T MRI.

MATERIALS AND METHODS

Twenty rabbits were included in this study. The strangulated SBO and MVO models were generated via surgical procedures in nine rabbits, and sham surgery was performed in two rabbits. The success of generating the models was confirmed via angiographic, macroscopic, and microscopic findings after the surgical procedure. MRI was performed before and 30 min after inducing mesenteric ischemia. T₁-weighted images (T₁WIs), T₂-weighted images (T₂WIs), and fat-suppressed T₂WIs (FS-T₂WIs) were obtained using the BLADE technique, and fat-suppressed T₁WIs (FS-T₁WIs) were obtained. The signal intensities of the affected bowel before and after the surgical procedures were visually categorized as high, iso, and low intense compared with the findings for the normal bowel wall on all sequences. Bowel wall thickness was measured, and the signal intensity ratio (SI ratio) was calculated using the signal intensities of the bowel wall and psoas muscle.

RESULTS

Angiographic, macroscopic, and microscopic findings confirmed that all surgical procedures were successful. The ischemic bowel wall was thicker than the normal bowel. The bowel wall was thicker in the MVO model (3.17 ± 0.55 mm) than in the strangulated SBO model (2.26 ± 0.46 mm). The signal intensity and SI ratio of the bowel wall were significantly higher after the procedure than before the procedure on all sequences in both models. The mesentery adjacent to the ischemic bowel loop exhibited a high signal intensity in all animals on FS-T₂WIs.

CONCLUSION

Non-contrast MRI can be used to evaluate mesenteric ischemia caused by strangulated SBO and MVO. FS-T₂WIs represented the best modality for depicting the high signal intensity in the bowel wall and mesentery caused by ischemia.

Comparison of 2D BLADE Turbo Gradient- and Spin-Echo and 2D Spin-Echo Echo-Planar Diffusion-Weighted Brain MRI at 3 T: Preliminary Experience in Children

RATIONALE AND OBJECTIVES

We describe our preliminary experience using a 2D turbo gradient- and spin-echo (TGSE) diffusion-weighted (DW) pulse sequence with non-Cartesian BLADE trajectory at 3 T in pediatric patients. We compared the TGSE BLADE to conventional DW spin-echo echo-planar imaging (SE-EPI) in pediatric brain imaging, assessing the presence of artifacts from signal pile-ups, geometric distortion, motion, susceptibility from air-tissue interface, shunts and orthodontia, and diagnostic image quality.

MATERIALS AND METHODS

Data were acquired in 53 patients (10.4 ± 7.9 years). All DW imaging data were acquired precontrast, with SE-EPI first. A four-point scale for rating was used-1 (best) and 4 (worst). A neuroradiologist scored the two sequences and further noted whether the TGSE BLADE approach or SE-EPI was preferred in each case. Apparent diffusion coefficients were compared quantitatively between the two sequences in a subset of 16 patients, in 41 separate regions of interests including caudate nucleus, putamen, globus pallidus, thalamus, and pathological areas.

RESULTS

In 43.4% of the cases, TGSE BLADE was preferred; in 49.1% of the cases, both sequences were preferred equally. Average scores for SE-EPI were 2.2 ± 0.8 versus TGSE's 1.2 ± 0.4 in assessing diagnostic quality (p < 0.05). Motion artifacts were minimal on both sequences in 92.5% of the cases. In the TGSE BLADE scores, no case received a "4" for significant artifacts with marginally acceptable image quality. Apparent diffusion coefficients values between the two sequences were statistically similar, with a linear regression slope of 0.92 (r² = 0.97).

CONCLUSION

TGSE BLADE DW imaging exhibited less geometric distortion in the brain and reduced signal pile-ups in areas of high susceptibility than conventional SE-EPI.

Denoising spinal cord fMRI data: Approaches to acquisition and analysis

Functional magnetic resonance imaging (fMRI) of the human spinal cord is a difficult endeavour due to the cord's small cross-sectional diameter, signal drop-out as well as image distortion due to magnetic field inhomogeneity, and the confounding influence of physiological noise from cardiac and respiratory sources. Nevertheless, there is great interest in spinal fMRI due to the spinal cord's role as the principal sensorimotor interface between the brain and the body and its involvement in a variety of sensory and motor pathologies. In this review, we give an overview of the various methods that have been used to address the technical challenges in spinal fMRI, with a focus on reducing the impact of physiological noise. We start out by describing acquisition methods that have been tailored to the special needs of spinal fMRI and aim to increase the signal-to-noise ratio and reduce distortion in obtained images. Following this, we concentrate on image processing and analysis approaches that address the detrimental effects of noise. While these include variations of standard pre-processing methods such as motion correction and spatial filtering, the main focus lies on denoising techniques that can be applied to task-based as well as resting-state data sets. We review both model-based approaches that rely on externally acquired respiratory and cardiac signals as well as data-driven approaches that estimate and correct for noise using the data themselves. We conclude with an outlook on techniques that have been successfully applied for noise reduction in brain imaging and whose use might be beneficial for fMRI of the human spinal cord.

Magnetic Resonance Enterography in Crohn׳s Disease

Over the past decade, magnetic resonance (MR) enterography has become established as the first-line imaging test for patients with Crohn׳s disease. This article reviews the role of MR enterography in assessing the extent and activity of Crohn׳s disease at baseline and on treatment follow-up. It discusses the role of diffusion-weighted imaging, and the recent introduction of MR scoring systems to facilitate noninvasive objective assessment of disease activity and cumulative bowel damage.

Application of a protocol for magnetic resonance spectroscopy of adrenal glands: an experiment with over 100 cases

Objective

To evaluate a protocol for two-dimensional (2D) hydrogen proton (1H) magnetic resonance spectroscopy (MRS) (Siemens Medical Systems; Erlangen, Germany) in the detection of adrenal nodules and differentiation between benign and malignant masses (adenomas, pheochromocytomas, carcinomas and metastases).

Materials and Methods

A total of 118 patients (36 men; 82 women) (mean age: 57.3 ± 13.3 years) presenting with 138 adrenal nodules/masses were prospectively assessed. A multivoxel system was utilized with a 2D point-resolved spectroscopy/chemical shift imaging sequence. The following ratios were calculated: choline (Cho)/creatine (Cr), 4.0–4.3/Cr, lipid (Lip)/Cr, Cho/Lip and lactate (Lac)/Cr.

Results

2D-1H-MRS was successful in 123 (89.13%) lesions. Sensitivity and specificity values observed for the ratios and cutoff points were the following: Cho/Cr ≥ 1.2, 100% sensitivity, 98.2% specificity (differences between adenomas/pheochromocytomas and carcinomas/ metastases); 4.0–4.3 ppm/Cr ≥ 1.5, 92.3% sensitivity, 96.9% specificity (differences between carcinomas/pheochromocytomas and adenomas/metastases); Lac/Cr ≤ –7.449, 90.9% sensitivity and 77.8% specificity (differences between pheochromocytomas and carcinomas/adenomas).

Conclusion

Information provided by 2D-1H-MRS were effective and allowed for the differentiation between adrenal masses and nodules in most cases of lesions with > 1.0 cm in diameter.

CINE turbo spin echo imaging

High-resolution turbo spin echo (TSE) images have demonstrated important details of carotid artery morphology; however, it is evident that pulsatile blood and wall motion related to the cardiac cycle are still significant sources of image degradation. Although ECG gating can reduce artifacts due to cardiac-induced pulsations, gating is rarely used because it lengthens the acquisition time and can cause image degradation due to nonconstant repetition time. This work introduces a relatively simple method of converting a conventional TSE acquisition into a retrospectively ECG-correlated cineTSE sequence. The cineTSE sequence generates a full sequence of ECG-correlated images at each slice location throughout the cardiac cycle in the same scan time that is conventionally used by standard TSE sequences to produce a single image at each slice location. The cineTSE images exhibit reduced pulsatile artifacts associated with a gated sequence but without the increased scan time or associated nonconstant repetition time effects.