Standard T1-weighted Sequences Research Articles

Breath-hold High-resolution T1-weighted Gradient Echo Liver MR Imaging with Compressed Sensing Obtained during the Gadoxetic Acid-enhanced Hepatobiliary Phase: Image Quality and Lesion Visibility Compared with a Standard T1-weighted Sequence.

To evaluate the feasibility of breath-hold (BH) high-resolution (HR) T1-weighted gradient echo hepatobiliary phase (HBP) imaging using compressed sensing (CS) in gadoxetic acid-enhanced liver MRI in comparison with standard HBP imaging using parallel imaging (PI). The study included 122 patients with liver tumors with hypointensity in the HBP who underwent both HR HBP imaging with CS and standard HBP imaging with PI. Two radiologists evaluated the liver edge sharpness, hepatic vessel conspicuity, bile duct conspicuity, image noise, and overall image quality, as well as the lesion conspicuity on HR and standard HBP imaging and the contrast-enhanced (CE) MR cholangiography (MRC) image quality reconstructed from HBP images. As a quantitative analysis, the SNR of the liver and the liver to lesion signal intensity ratio (LLSIR) were also determined. The liver edge sharpness, hepatic vessel conspicuity, bile duct conspicuity, and overall image quality as well as the lesion conspicuity and the LLSIR on HR HBP imaging with CS were significantly higher than those on standard HBP imaging (all of P < 0.001). The image quality of CE-MRC reconstructed from HR HBP imaging with CS was also significantly higher than that from standard HBP imaging (P < 0.001). Conversely, the SNR of liver in standard HBP was significantly higher than that in HR HBP with CS (P < 0.001). BH HR HBP imaging with CS provided an improved overall image quality, lesion conspicuity, and CE-MRC visualization when compared with standard HBP imaging without extending the acquisition time.

Ultrashort echo time MRI of the lung in children and adolescents: comparison with non-enhanced computed tomography and standard post-contrast T1w MRI sequences

ObjectivesTo compare the diagnostic value of ultrashort echo time (UTE) magnetic resonance imaging (MRI) for the lung versus the gold standard computed tomography (CT) and two T1-weighted MRI sequences in children.MethodsTwenty-three patients with proven oncologic disease (14 male, 9 female; mean age 9.0 + / − 5.4 years) received 35 low-dose CT and MRI examinations of the lung. The MRI protocol (1.5-T) included the following post-contrast sequences: two-dimensional (2D) incoherent gradient echo (GRE; acquisition with breath-hold), 3D volume interpolated GRE (breath-hold), and 3D high-resolution radial UTE sequences (performed during free-breathing). Images were evaluated by considering image quality as well as distinct diagnosis of pulmonary nodules and parenchymal areal opacities with consideration of sizes and characterisations.ResultsThe UTE technique showed significantly higher overall image quality, better sharpness, and fewer artefacts than both other sequences. On CT, 110 pulmonary nodules with a mean diameter of 4.9 + / − 2.9 mm were detected. UTE imaging resulted in a significantly higher detection rate compared to both other sequences (p < 0.01): 76.4% (84 of 110 nodules) for UTE versus 60.9% (67 of 110) for incoherent GRE and 62.7% (69 of 110) for volume interpolated GRE sequences. The detection of parenchymal areal opacities by the UTE technique was also significantly higher with a rate of 93.3% (42 of 45 opacities) versus 77.8% (35 of 45) for 2D GRE and 80.0% (36 of 45) for 3D GRE sequences (p < 0.05).ConclusionThe UTE technique for lung MRI is favourable in children with generally high diagnostic performance compared to standard T1-weighted sequences as well as CT.Key Points• Due to the possible acquisition during free-breathing of the patients, the UTE MRI sequence for the lung is favourable in children.• The UTE technique reaches higher overall image quality, better sharpness, and lower artefacts, but not higher contrast compared to standard post-contrast T1-weighted sequences.• In comparison to the gold standard chest CT, the detection rate of small pulmonary nodules small nodules ≤ 4 mm and subtle parenchymal areal opacities is higher with the UTE imaging than standard T1-weighted sequences.

Implementation of a sagittal T2-weighted DIXON turbo spin-echo sequence may shorten MRI acquisitions in the emergency setting of suspected spinal bleeding

BackgroundMagnetic resonance imaging (MRI) is the modality of choice for evaluating soft tissue damage along the spine in the emergency setting, yet access and fast protocol availability are limited. We assessed the performance of a sagittal T2-weighted DIXON turbo spin-echo sequence and investigated whether additional standard sagittal T1-weighted sequences are necessary in suspected spinal fluid collections/bleedings.MethodsSeventy-four patients aged 62.9 ± 19.3 years (mean ± standard deviation) with MRI including a sagittal T2-weighted DIXON sequence and a T1-weighted sequence were retrospectively included. Thirty-four patients (45.9%) showed a spinal fluid collection/bleeding. Two layouts (layout 1: fat-only and water-only and in-phase images of the DIXON sequence and T1-weighted images; layout 2: fat-only and water-only and in-phase images of the DIXON sequence) were evaluated by three readers (R1, R2, and R3) concerning presence of spinal fluid collections/bleedings and diagnostic confidence from 1 (very low confidence) to 5 (very high confidence). χ2 and κ statistics were used.ResultsThere was no difference in detecting spinal fluid collections/bleedings between the layouts (R1 and R2 detected all, R3 missed one spinal fluid collection/bleeding in the same patient in both layouts). Confidence was high (layout 1, R1 4.26 ± 0.81, R2 4.28 ± 0.81, R3 4.32 ± 0.79; layout 2, R1 3.93 ± 0.70, R2 4.09 ± 0.86, R3 3.97 ± 0.73), with higher inter-reader agreement for layout 1 (κ 0.691–0.780) than for layout 2 (κ 0.441–0.674).ConclusionsA sagittal T2-weighted DIXON sequence provides diagnostic performance similar to a protocol including standard T1-weighted sequences.

High Acceleration Three-Dimensional T1-Weighted Dual Echo Dixon Hepatobiliary Phase Imaging Using Compressed Sensing-Sensitivity Encoding: Comparison of Image Quality and Solid Lesion Detectability with the Standard T1-Weighted Sequence.

ObjectiveTo compare a high acceleration three-dimensional (3D) T1-weighted gradient-recalled-echo (GRE) sequence using the combined compressed sensing (CS)-sensitivity encoding (SENSE) method with a conventional 3D GRE sequence using SENSE, with respect to image quality and detectability of solid focal liver lesions (FLLs) in the hepatobiliary phase (HBP) of gadoxetic acid-enhanced liver MRI.Materials and MethodsA total of 217 patients with gadoxetic acid-enhanced liver MRI at 3T (54 in the preliminary study and 163 in the main study) were retrospectively included. In the main study, HBP imaging was done twice using the standard mDixon-3D-GRE technique with SENSE (acceleration factor [AF]: 2.8, standard mDixon-GRE) and the high acceleration mDixon-3D GRE technique using the combined CS-SENSE technique (CS-SENSE mDixon-GRE). Two abdominal radiologists assessed the two MRI data sets for image quality in consensus. Three other abdominal radiologists independently assessed the diagnostic performance of each data set and its ability to detect solid FLLs in 117 patients with 193 solid nodules and compared them using jackknife alternative free-response receiver operating characteristics (JAFROC).ResultsThere was no significant difference in the overall image quality. CS-SENSE mDixon-GRE showed higher image noise, but lesser motion artifact levels compared with the standard mDixon-GRE (all p < 0.05). In terms of lesion detection, reader-averaged figures-of-merit estimated with JAFROC was 0.918 for standard mDixon-GRE, and 0.953 for CS-SENSE mDixon-GRE (p = 0.142). The non-inferiority of CS-SENSE mDixon-GRE over standard mDixon-GRE was confirmed (difference: 0.064 [−0.012, 0.081]).ConclusionThe CS-SENSE mDixon-GRE HBP sequence provided comparable overall image quality and non-inferior solid FFL detectability compared with the standard mDixon-GRE sequence, with reduced acquisition time.

Improved detection of erosions in the sacroiliac joints on MRI with volumetric interpolated breath-hold examination (VIBE): results from the SIMACT study.

To compare the performance of a new three-dimensional MRI sequence (volumetric interpolated breath-hold examination; MR-VIBE) with a conventional T1-weighted sequence (MR-T1) for the detection of erosions in the sacroiliac joints (SIJs) using low-dose CT (ldCT) as reference. ldCT and T1-MRI and MR-VIBE of 110 prospectively included patients with low back pain and suspected axial spondyloarthritis (axSpA) were scored for erosions by two readers. The presence of erosions on the patients' level, the erosion sum score, sensitivity and specificity of both MRI sequences using ldCT as a reference as well as agreement between the readers were assessed. MR-VIBE had a higher sensitivity than MR-T1 (95% vs 79%, respectively) without a decrease in specificity (93% each). MR-VIBE compared with MR-T1 identified 16% more patients with erosions (36 vs 30 of 38 patients with positive ldCT findings). The erosion sum score was also higher for MR-VIBE (8.1±9.3) than MR-T1 (6.7±8.4), p=0.003. The agreement on erosion detection was also higher for MR-VIBE (κ=0.71) compared with MRI-T1 (κ=0.56). VIBE detected erosions in the SIJs with higher sensitivity without a loss of specificity and superior reliability compared with a standard T1-weighted sequence. Its value for the diagnosis of axSpA has still to be determined.

Increase of Intra-abdominal Adipose Tissue in Pediatric Crohn Disease.

Recent evidence points toward an active immunological role of intra-abdominal adipose tissue in Crohn disease (CD). We quantified the abdominal adipose tissue compartments using magnetic resonance imaging (MRI) in 27 pediatric patients with CD compared with 14 controls undergoing MRI examination for other reasons. Total (TAAT), subcutaneous (SCAT) and intra-abdominal (IAAT) adipose tissue areas were measured by semiautomatic segmentation on a transverse slice centered on the umbilicus (mean ± standard deviation in square centimeter) using standard T1-weighted sequences. IAAT/TAAT and IAAT/height ratios were calculated and analyzed for associations with disease duration, phenotype, or therapy. Patients with CD (median age 15.0 years, range 7.7-17.9, 18/27 boys, median disease duration 29 months, range 0-136) compared to controls (median age 13.9 years, range 3.3-17.8, 4/14 boys) had higher IAAT area (42.3 ± 21.0 vs 28.7 ± 11.6, P = 0.0494) but similar SCAT and TAAT areas (104.6 ± 72.8 vs 96.5 ± 50.8, P = 0.8170 and 146.9 ± 87.3 vs 125.3 ± 61.5, P = 0.7417, respectively). IAAT/TAAT ratio was higher in patients with CD compared to controls (0.32 ± 0.10 vs 0.24 ± 0.04, P = 0.0081). Patients with disease duration >2 years (n = 14) had higher IAAT/TAAT ratio than those with shorter disease and controls (0.35 ± 0.10 vs 0.28 ± 0.08, P = 0.0288 and 0.24 ± 0.04, P = 0.0009, respectively). In these patients, increased IAAT/height ratio was associated with complicated disease (P = 0.043, r = 0.573). No association was found between IAAT/TAAT ratio and actual disease activity or therapy. IAAT is increased in pediatric CD and correlates with disease duration. Assessment of IAAT accumulation may be considered in future MRI scores for inflammation and bowel damage in CD and during follow-up of different therapeutic interventions.

Chapter 11 - Imaging of pituitary pathology

Modern imaging techniques play a vital role in the diagnosis, surveillance, and treatment monitoring of patients with pituitary disease. For its high soft tissue contrast, magnetic resonance (MR) imaging provides detailed information about the localization and extent of a lesion. It is thus, to date, the most important imaging technique for documenting or ruling out structural lesions. It is usually the first and only imaging procedure to be employed in pituitary pathology. While large pituitary adenomas are reliably depicted in standard T1-weighted sequences, small microadenomas, such as in Cushing's disease, may only become visible if repeat studies, sophisticated techniques and high-field scanners are employed. For monitoring treatment effects after surgical procedures, drug applications, or irradiation, follow-up studies with identical parameters should be employed, preferably at the same investigation site. Some space is devoted to intraoperative imaging, which not only allows assessment of how radical tumor resection needs to be during pituitary tumor surgery, but also provides extremely accurate structural data for neuronavigation. Less frequent lesions, such as craniopharyngiomas, meningiomas, germ cell tumors, gliomas, skull base tumors, hypothalamic hamartomas, vascular malformations, inflammatory and developmental lesions and other, even less frequent pathologies should be considered in the differential diagnosis. The particular strength of computed tomography (CT) is the direct depiction of calcification, a weakness of MRI, and the high resolution of bone structures at the skull base. This chapter presents the characteristics of both frequent and less commonly encountered tumoral lesions, with an emphasis on computed tomography and magnetic resonance imaging.

Compensation of RF field and receiver coil induced inhomogeneity effects in abdominal MR images by a priori knowledge on the human adipose tissue distribution

To reliably compensate bias field effects in abdominal areas to accurately quantify visceral adipose tissue using standard T1-weighted sequences on MR scanners with up to 3 Tesla (T) field strength. Compensation is achieved in two steps: The bias field is first estimated by picking and fitting sampling points from the subcutaneous adipose tissue, using active contours and a thin plate fitting spline. Then, additional sampling points from visceral adipose tissue compartments are detected by thresholding and the bias field estimation is refined. It was compared with an established method using a simulated abdominal image and real 3T data. At low bias field amplitudes (40-50%), the simulation study showed a good reduction of the mean coefficients of variance (CV) for both approaches (>80%). At higher amplitudes, the CV reduction was significantly higher for our approach (83.6%), compared with LEMS (54.3%). In the real data study, our approach showed reliable reduction of the inhomogeneities, while the LEMS algorithm sometimes even amplified the inhomogeneities. The proposed method enables accurate and reliable segmentation of abdominal adipose tissue using simple thresholding techniques, even in severely corrupted images slices, obtained when using high field strengths and/or phased-array coils.

Enhancement of thoracic masses using nonionic MR contrast agents.

This study evaluated the effect of a new nonionic MR contrast medium, gadodiamide injection (Omniscan; Sanofi-Winthrop), on enhancement of thoracic masses on T1-weighted SE images. Gadodiamide injection was administered intravenously at a dose of 0.2 mmol/kg to 26 patients with thoracic masses. The T1-weighted images with and without fat suppression and T2-weighted images obtained before contrast medium injection were compared with T1-weighted images obtained at 5, 30, and 45 min and a T1-weighted fat-suppressed image at 10 min after administration of the contrast medium. Enhancement of the thoracic masses and image quality were quantified by measuring signal intensity, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) using muscle and fat as reference tissues. The SNR of the masses increased significantly (p < 0.001) following contrast material injection both on standard T1-weighted sequences and on T1-weighted fat-suppressed images when compared with the precontrast T1-weighted images with and without fat suppression. The CNR (reference tissue muscle) improved significantly (p < 0.001) after contrast medium injection and persisted for 45 min on T1-weighted images compared with those prior to contrast medium. However, there was no significant difference in CNR between the T2-weighted images obtained before and the T1-weighted images obtained after contrast agent administration. On the other hand, the SNR of contrast-enhanced images was significantly better than that of the T2-weighted images. When fat was used as a reference tissue, CNR of the thoracic masses decreased significantly. This study shows that gadodiamide injection caused significant enhancement of thoracic masses on T1-weighted images, which rendered high signal intensity to the masses similar to the appearance on T2-weighted images. In comparison with the T2-weighted images, SNR was significantly improved.

Synergistic Enhancement of MRI with Gd-DTPA and Magnetization Transfer

Magnetization transfer (MT) between protons of macromolecules and protons of water molecules is a recently introduced mechanism for tissue contrast in MR imaging. The MT effect is strong in tissues where there is an efficient cross relaxation between macromolecular protons and water protons and where this interaction is the dominant source of relaxation. Paramagnetic ions shorten relaxation times and decrease the MT effect. These two facts led to the assumption that, in the case of contrast enhanced MRI, the combination of the T1-weighted imaging method and the MT technique may yield increased contrast, compared with standard methods. The synergistic effect is demonstrated in this work with studies of egg white samples and by imaging three patients with different brain pathologies. The lesion-to-white matter contrasts, with standard T1-weighted sequences with and without the MT effect, were compared before and after the introduction of Gd-DTPA. In each case the synergistic effect of T1 weighting and MT improved the contrast enhancement provided with Gd-diethylenetriamine pentaacetic acid.

Dynamic magnetic resonance imaging of the temporomandibular joint using FLASH sequences.

Magnetic resonance imaging (MRI) is a suitable modality for the visualization of the temporomandibular joint (TMJ) in both normal and pathologic conditions. Until recently, MRI had been unable to provide diagnostic dynamic images of the TMJ during opening. A series of 30 TMJ MRI examinations of 17 symptomatic patients and two normal volunteers (15 to 43 years old; 14 men and five women) was performed. Fast low angle shot (FLASH) sequences were used to provide a series of dynamic images of the TMJ in various phases of opening. In 30% of the joint examined, FLASH sequences contributed clinically significant information not available with standard T1-weighted sequences. These results suggest that FLASH images are particularly useful in distinguishing normal disc variants from pathologic conditions in which the disc is displaced anteriorly to a mild extent. The short imaging time of FLASH sequences decreases motion artifact in patients who have difficulty remaining still during the examination.