T1-weighted Gradient Recalled Echo Sequence Research Articles

Free-Breathing High-Resolution, Swap-Free, and Motion-Corrected Water/Fat Separation in Pediatric Abdominal MRI

Objectives The T1-weighted GRE (gradient recalled echo) sequence with the Dixon technique for water/fat separation is an essential component of abdominal MRI (magnetic resonance imaging), useful in detecting tumors and characterizing hemorrhage/fat content. Unfortunately, the current implementation of this sequence suffers from several problems: (1) low resolution to maintain high pixel bandwidth and minimize chemical shift; (2) image blurring due to respiratory motion; (3) water/fat swapping due to the natural ambiguity between fat and water peaks; and (4) off-resonance fat blurring due to the multipeak nature of the fat spectrum. The goal of this study was to evaluate the image quality of water/fat separation using a high-resolution 3-point Dixon golden angle radial acquisition with retrospective motion compensation and multipeak fat modeling in children undergoing abdominal MRI. Materials and Methods Twenty-two pediatric patients (4.2 ± 2.3 years) underwent abdominal MRI on a 3 T scanner with routine abdominal protocol and with a 3-point Dixon radial-VIBE (volumetric interpolated breath-hold examination) sequence. Field maps were calculated using 3D graph-cut optimization followed by fat and water calculation from k-space data by iteratively solving an optimization problem. A 6-peak fat model was used to model chemical shifts in k-space. Residual respiratory motion was corrected through soft-gating by weighting each projection based on the estimated respiratory motion from the center of the k-space. Reconstructed images were reviewed by 3 pediatric radiologists on a PACS (picture archiving and communication systems) workstation. Subjective image quality and water/fat swapping artifact were scored by each pediatric radiologist using a 5-point Likert scale. The VoL (variance of Laplacian) of the reconstructed images was used to objectively quantify image sharpness. Results Based on the overall Likert scores, the images generated using the described method were significantly superior to those reconstructed by the conventional 2-point Dixon technique (P < 0.05). Water/fat swapping artifact was observed in 14 of 22 patients using 2-point Dixon, and this artifact was not present when using the proposed method. Image sharpness was significantly improved using the proposed framework. Conclusions In smaller patients, a high-quality water/fat separation with sharp visualization of fine details is critical for diagnostic accuracy. High-resolution golden angle radial-VIBE 3-point Dixon acquisition with 6-peak fat model and soft-gated motion correction offers improved image quality at the expense of an additional ~1-minute acquisition time. Thus, this technique offers the potential to replace the conventional 2-point Dixon technique.

Image quality of the CAIPIRINHA-Dixon-TWIST-VIBE technique for ultra-fast breast DCE-MRI: Comparison with the conventional GRE technique

PurposeThe aim of this study was to evaluate image quality of the CAIPIRINHA-Dixon-TWIST-Volume-Interpolated Breath-hold Examination (CDT-VIBE) technique for ultra-fast breast dynamic contrast enhanced (DCE) MRI with respect to conventional Gradient-Recalled Echo (GRE) technique. MethodsA total of 58 patients underwent a DCE-MRI based on CDT-VIBE sequence (temporal resolution: 11.9 s), immediately followed by 1 phase of a conventional T1 weighted GRE sequence (acquisition time: 68 s). The Signal-to-Noise Ratio (SNR) on phantom images, lesion/parenchyma signal ratio (LPSR), image quality, and morphological characterization were compared between the last phase of CDT-VIBE and conventional GRE images. The image quality was assessed by visual grading analysis (VGA). Reader agreement was assessed using Kappa analysis. ResultsThere was no significant difference in SNR (phantom) or LPSR (patient) between CDT-VIBE and conventional GRE images (P > 0.05). Significant parallel acquisition technique (PAT) noise and mild blurriness was observed on CDT-VIBE images. Visual grading analysis (VGA) confirmed significantly worse ratings for CDT-VIBE compared to the conventional GRE sequence in terms of PAT noise, lesion’s internal feature clarity, and therefore overall image quality (area under contrast curve [AUC] values: 0.578 ‒ 0.764, P < 0.05), but edge sharpness and lesion conspicuity were equivalent (P > 0.05). Kappa analysis revealed good agreement on image quality scores (к = 0.725 ‒ 0.908) and on morphologic terms (к = 0.745–1.000). ConclusionThe CDT-VIBE sequence provides excellent spatial resolution and adequate image quality in ultra-fast breast DCE-MRI. Further improvement in PAT noise and internal structure blurriness may be necessary.

3-T direct MR arthrography of the wrist: Value of finger trap distraction to assess intrinsic ligament and triangular fibrocartilage complex tears

PurposeTo determine the value of applying finger trap distraction during direct MR arthrography of the wrist to assess intrinsic ligament and triangular fibrocartilage complex (TFCC) tears. Materials and methodsTwenty consecutive patients were prospectively investigated by three-compartment wrist MR arthrography. Imaging was performed with 3-T scanners using a three-dimensional isotropic (0.4mm) T1-weighted gradient-recalled echo sequence, with and without finger trap distraction (4kg). In a blind and independent fashion, two musculoskeletal radiologists measured the width of the scapholunate (SL), lunotriquetral (LT) and ulna-TFC (UTFC) joint spaces. They evaluated the amount of contrast medium within these spaces using a four-point scale, and assessed SL, LT and TFCC tears, as well as the disruption of Gilula's carpal arcs. ResultsWith finger trap distraction, both readers found a significant increase in width of the SL space (mean Δ=+0.1mm, p≤0.040), and noticed more contrast medium therein (p≤0.035). In contrast, the differences in width of the LT (mean Δ=+0.1mm, p≥0.057) and UTFC (mean Δ=0mm, p≥0.728) spaces, as well as the amount of contrast material within these spaces were not statistically significant (p=0.607 and ≥0.157, respectively). Both readers detected more SL (Δ=+1, p=0.157) and LT (Δ=+2, p=0.223) tears, although statistical significance was not reached, and Gilula's carpal arcs were more frequently disrupted during finger trap distraction (Δ=+5, p=0.025). ConclusionThe application of finger trap distraction during direct wrist MR arthrography may enhance both detection and characterisation of SL and LT ligament tears by widening the SL space and increasing the amount of contrast within the SL and LT joint spaces.

Dorsal Fractures of the Triquetrum: MRI Findings With an Emphasis on Dorsal Carpal Ligament Injuries

The objective of our study was to report the MRI findings in dorsal fractures of the triquetrum, with an emphasis on dorsal carpal ligament injuries. A total of 21 patients (16 men, five women; mean age, 41.9 years) with acute or subacute (≤ 6 weeks) dorsal triquetral fractures on radiography and MRI were included in this two-center retrospective study. MRI of the wrist was performed on 3-T units with transverse T1-weighted, coronal or transverse (or both) fat-suppressed T2weighted, transverse gadolinium-enhanced fat-suppressed T1-weighted turbo spin-echo, and 3D gadolinium-enhanced fat-suppressed T1-weighted gradient-recalled echo sequences. Three musculoskeletal radiologists evaluated the ulnar styloid process index (USPI) on radiographs and the following MRI features: fracture pattern (types 1-6), bone fragment size and displacement, bone marrow edema distribution, and dorsal carpal ligament tears. Eight type 1, one type 2, six type 3, five type 4, and one type 5 fractures were identified. These fractures were associated with 14 (66.7%), 17 (81.0%), and 16 (76.2%) tears of the dorsal radiocarpal, ulnotriquetral, and intercarpal ligaments, respectively. There was no correlation between bone marrow edema distribution and dorsal carpal ligament injuries (all p > 0.05). The mean (± SD) bone fragment volume and displacement were 205 ± 157 mm(3) and 1.0 ± 1.1 mm, respectively. The mean USPI was 0.21 ± 0.10. Dorsal fractures of the triquetrum are frequently associated with dorsal carpal ligament injuries. Bone marrow edema distribution is not correlated with these ligament tears.

Direct MR arthrography of the shoulder under axial traction: Feasibility study to evaluate the superior labrum‐biceps tendon complex and articular cartilage

To assess the value of adding axial traction to direct MR arthrography of the shoulder, in terms of subacromial and glenohumeral joint space widths, and coverage of the superior labrum-biceps tendon complex and articular cartilage by contrast material. Twenty-one patients investigated by direct MR arthrography of the shoulder were prospectively included. Studies were performed with a 3 Tesla (T) unit and included a three-dimensional isotropic fat-suppressed T1-weighted gradient-recalled echo sequence, without and with axial traction (4 kg). Two radiologists independently measured the width of the subacromial, superior, and inferior glenohumeral joint spaces. They subsequently rated the amount of contrast material around the superior labrum-biceps tendon complex and between glenohumeral cartilage surfaces, using a three-point scale: 0 = no, 1 = partial, 2 = full. Under traction, the subacromial (Δ = 2.0 mm, P = 0.0003), superior (Δ = 0.7 mm, P = 0.0001) and inferior (Δ = 1.4 mm, P = 0.0006) glenohumeral joint space widths were all significantly increased, and both readers noted significantly more contrast material around the superior labrum-biceps tendon complex (P = 0.014), and between the superior (P = 0.001) and inferior (P = 0.025) glenohumeral cartilage surfaces. Direct MR arthrography of the shoulder under axial traction increases subacromial and glenohumeral joint space widths, and prompts better coverage of the superior labrum-biceps tendon complex and articular cartilage by contrast material.

DISTAL INTERPHALANGEAL ARTICULAR CARTILAGE ASSESSMENT USING LOW-FIELD MAGNETIC RESONANCE IMAGING

The suitability of low-field magnetic resonance (MR) imaging for assessment of articular cartilage has been questioned, based on insufficient image quality. The purposes of this study were to describe the MR anatomy of the normal distal interphalangeal (DIP) cartilage, and to evaluate the sensitivity and accuracy of low-field MR imaging for identification of cartilage erosions that were created ex vivo. Imaging sequences included sagittal and dorsal multiple-oblique T1-weighted gradient-recalled echo (GRE) and sagittal dual echo sequences. In the thickest regions, normal cartilage appeared as a trilaminar structure on high-resolution T1-weighted GRE sequences. All 8 mm large full-thickness erosions were correctly identified (100% sensitivity and accuracy) using T1-weighted GRE sequences. Sensitivity and accuracy ranged from 80% to 100% and 10% to 80%, respectively, for detecting focal full-thickness erosions and from 35% to 80% and 35% to 60%, respectively, for detecting partial thickness erosions, using T1-weighted GRE sequences. Superficial irregularities were not diagnosed using any sequence. Overall, fewer cartilage alterations were detected with sagittal dual echo sequences than with sagittal T1-weighted GRE sequences. The dorsal multiple-oblique plane was useful to detect linear dorsopalmar erosions. A combination of T1-weighted GRE sequences in two planes has potential for identification of severe DIP cartilage erosion in anesthetized horses using low-field MR imaging.

MR to assess renal function in children.

Renal function evaluation in the pediatric patient is generally based on scintigraphic examinations where a baseline gamma-camera renography is used to determine single kidney function, and diuresis renography is obtained to assess urinary drainage from the pelvicalyceal system. Magnetic resonance imaging also permits the evaluation of renal functional processes using fast dynamic sequences. Principally, an agent cleared by renal excretion is intravenously injected and its cortical uptake, parenchymal transport, and eventually its urinary excretion are followed with serial images. Different approaches have been presented most of which are based on T1-weighted gradient-recalled echo sequences with short TR and TE and a low flip angle obtained after intravenous injection of Gd-DTPA or Gd-DOTA. These techniques permit renal functional assessment using different qualitative and quantitative parameters; however, most of these methods are not suitable for the evaluation of urinary tract dilatation in infants and children. For the diagnostic work-up of children with congenital urinary tract obstruction and malformation a technique was developed which permits quantitative determination of single kidney function, in addition to evaluating urinary excretion disturbances analogous to that possible with scintigraphy.

MR imaging of the wrist in rheumatoid arthritis using gadobenate dimeglumine.

To determine the dosage of gadobenate dimeglumine (Gd-BOPTA) necessary for MRI of rheumatoid arthritis of the wrist. Seven wrists inflamed with rheumatoid arthritis were imaged using a dedicated 0.2-T MR unit. Four cumulative dosages of 0.0125, 0.025, 0.05 and 0.1 mmol/kg body weight (BW) Gd-BOPTA were tested. Three-dimensional T1-weighted gradient-recalled echo sequences (GRE; TR: 100 ms, TE: 18 ms, flip angle 90 degrees , 4:55 min) were acquired prior to an intravenous injection and after each additional dosage of Gd-BOPTA. Relative enhancement, signal-difference-to-noise ratios (SDNRs) and the size of the inflamed tissue were quantified. Three radiologists independently evaluated the image quality, the size and the contrast of the enhancing tissue. The readers agreed on a dose of 0.05 mmol/kg BW as satisfactory for the evaluation of the size of the inflammatory tissue and for determination of bone involvement (kappa = 0.9, P < 0.001). Highly inflammatory pannus was depicted with adequate image contrast using 0.025 mmol/kg BW Gd-BOPTA. According to the SDNR and relative enhancement findings, a dose of 0.05 mmol/kg BW suffices for both off-center and centered regions of tissue inflammation (t-test, P < 0.05). Gadolinium-BOPTA is an alternative contrast agent for MRI of rheumatoid disease. This study shows that a dose of 0.05 mmol/kg BW suffices at low field strength.

T-1 weighted sequences for hepatic mri: Re-evaluation using a phased array coil

The purpose of this study was to compare three T1-weighted sequences for hepatic magnetic resonance (MRI) imaging with the use of a body phased array coil. Three different T1-weighted MR sequences were compared: a conventional spin echo (CSE); half-Fourier spin echo (HFSE), and a gradient recalled echo (GRE). Three independent reviewers compared the sequences both quantitatively and qualitatively. The T1-weighted GRE sequence scored highest for overall image quality (p < 0.001), lesion conspicuity p = 0.012 , and yielded the highest contrast to noise (C/N) values. GRE T1-weighted images are the best for hepatic MRI.

The indeterminate breast mass: assessment using contrast enhanced magnetic resonance imaging

Magnetic resonance imaging of the breast was performed on 25 lesions in 24 patients. These lesions were indeterminate on clinical and mammographic examination. The imaging findings were compared with pathological results in all cases. Conventional T1 and T2 spin echo images provided a certain diagnosis in only one case. The pattern of signal enhancement following gadolinium diethylamine triamine pentaacetic acid injection as demonstrated by a T1-weighted gradient recalled echo sequence permitted accurate diagnosis of four recurrent carcinomas and 19 cases of non-malignant disease (17 postoperative scars and two cases of benign breast disease). One false positive diagnosis of cancer was made in a case of fibroadenoma. Dynamic contrast enhanced magnetic resonance imaging may have a role in the assessment of the indeterminate breast mass.