Advantages of a T1-Weighted Gradient-Recalled Echo (GRE) Sequence With a Radial 3D Sampling Approach Versus 2D Turbo Spin-Echo and Cartesian 3D GRE Sequences in Head and Neck MRI.

OBJECTIVE. The purpose of this study is to compare the image quality, including artifacts, of a T1-weighted gradient-recalled echo (GRE) MRI sequence with a radial sampling approach to that of both 2D turbo spin-echo (TSE) and cartesian 3D GRE MRI sequences performed in the head and neck region. MATERIALS AND METHODS. The retrospective study included 26 datasets of patients who underwent MRI examination for inflammatory or neoplastic diseases of the head and neck region performed using a 1.5-T system. All examination protocols comprised three fat-saturated T1-weighted sequences performed in the axial plane after contrast agent administration. Axial FOV and spatial resolution in plane and along the z-axis were recorded. Sequences were evaluated independently by two readers for qualitative and quantitative parameters, including homogeneity of fat saturation and discrimination of pharyngeal wall structures. Qualitative parameters were evaluated using a 5-point Likert scale. RESULTS. For comparison, mean values of Likert scale scores were generated from the two readers' data. Fat saturation was significantly better on the radial GRE sequences (1.942) than on the TSE (2.346; p = 0.002) and cartesian GRE (2.365; p = 0.008) sequences. The overall impact of foreign material artifacts was comparable among sequences (radial GRE, 1.731; TSE, 1.731 [p = 1.000]; cartesian GRE, 1.769 [p = 0.414]); however, on direct comparison, the mean area that was not evaluable because of susceptibility was smaller on radial GRE sequences (53.8 mm) than on TSE sequences (59.8 mm; p = 0.062) and cartesian GRE sequences (59.6 mm; p = 0.079). Overall image quality was 1.635 with the use of radial GRE, 2.423 with TSE (p = 0.000), and 2.500 with cartesian GRE (p = 0.000). CONCLUSION. For imaging of the head and neck region, radial GRE has several advantages, including improved fat saturation and reduced extent of susceptibility artifacts, compared with TSE and cartesian GRE, leading to improved overall image quality.

Image quality of low-radiation dose left atrial CT using filtered back projection and an iterative reconstruction algorithm: intra-individual comparison in unselected patients undergoing pulmonary vein isolation.

Background Computed tomography (CT) of the left atrium (LA) is performed prior to pulmonary vein isolation (PVI) to improve success of circumferential ablation for atrial fibrillation. The ablation procedure itself exposes patients to substantial radiation doses, therefore radiation dose reduction in pre-ablational imaging is of concern. Purpose To assess and compare diagnostic performance of low-radiation dose preprocedural CT in patients scheduled for PVI using two types of reconstruction algorithms. Material and Methods Forty-six patients (61 ± 10 years) scheduled for PVI were enrolled in this study irrespective of body-mass-index or cardiac rhythm at examination. An electrocardiographically triggered dual-source CT scan was performed. Filtered back projection (FBP) and iterative reconstruction (IR) algorithms were applied. Images were integrated into an electroanatomic mapping (EAM) system. Subjective image quality was scored independently by two readers on a five-point scale for both reconstruction algorithms (1 = excellent to 5 = non-diagnostic). Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and effective radiation dose were calculated. Results Data acquisition and EAM integration were successful in all patients. Median image quality score was 1 for both FBP (quartiles = 1, 1.62; range = 1-3) and IR (quartiles = 1, 1.5; range = 1-3). Mean SNR was 7.61 ± 2.14 for FBP and 9.02 ± 2.69 for IR. Mean CNR was 5.92 ± 1.80 for FBP and 6.95 ± 2.29 for IR. Mean effective radiation dose was 0.3 ± 0.1 mSv. Conclusion At a radiation dose of 0.3 ± 0.1 mSv, high-pitch dual-source CT yields LA images of consistently high quality using both FBP and IR. IR raises SNR and CNR without significantly improving subjective image quality.

Correlation of Native Liver Parenchyma T1 and T2 Relaxation Times and Liver Synthetic Function Tests: A Pilot Study.

MR relaxometry increasingly contributes to liver imaging. Studies on native relaxation times mainly describe relation to the presence of fibrosis. The hypothesis was that relaxation times are also influenced by other inherent factors, including changes in liver synthesis function. With the approval of the local ethics committee and written informed consent, data from 94 patients referred for liver MR imaging, of which 20 patients had cirrhosis, were included. Additionally to standard sequences, both native T1 and T2 parametric maps and T1 maps in the hepatobiliary phase of gadoxetate disodium were acquired. Associations with laboratory variables were assessed. Altogether, there was a negative correlation between albumin and all acquired relaxation times in cirrhotic patients. In non-cirrhotic patients, only T1 values exhibited a negative correlation with albumin. In all patients, bilirubin correlated significantly with post-contrast T1 relaxation times, whereas native relaxation times correlated only in cirrhotic patients. Evaluating patients with pathological INR values, post-contrast relaxation times were significantly higher, whereas native relaxation times did not correlate. In conclusion, apart from confirming the value of hepatobiliary phase T1 mapping, our results show a correlation of native T1 with serum albumin even in non-cirrhotic liver parenchyma, suggesting a direct influence of liver's synthesis capacity on T1 relaxation times.

Native T1 mapping for assessment of the perilesional zone in metastases and benign lesions of the liver.

Adjacent to hepatic metastases, liver parenchyma is often histopathologically altered even if its visual appearance on native magnetic resonance (MR) images is blunt. Yet, relaxation properties in MR imaging may show structural changes prior to visual alteration, and therefore, the aim of this study was to investigate whether T1 relaxation times in the perilesional zone differ between metastases and benign lesions. A total of 113 patients referred for MRI were included prospectively. Images were assessed for metastases, solid benign lesions and cysts, and regions-of-interest were drawn on T1 maps including the focal lesion and a close (inner perilesional zone = IPZ) and a larger perilesional zone (outer perilesional zone = OPZ). Simple ratios between these zones, as well as a gradient ratio between the IPZ and the entire perilesional zone (EPZ) were calculated. Within the collective, 44 patients had lesions of one or two entities. For metastases, the simple ratio between IPZ and OPZ as well as the mean EPZ gradient was significantly higher than for both solid benign lesions and cysts. Lesion size was not a significant covariate. We conclude, that native T1 properties of the perilesional zones differ significantly between malignant and both solid and cystic benign lesions.

Value of susceptibility-weighted imaging for the assessment of angle measurements reflecting hip morphology.

Radiographs are the clinical first line imaging modality for evaluating hip morphology and pathology. MRI offers additional information and is the method of choice to evaluate soft tissue, bone marrow and preradiographic signs of osteoarthritis. Radiographs are used to measure the most morphometric parameters. The aim of this study was to compare susceptibility weighted MRI (SWMR) with radiographs to evaluate hip morphology. 40 Patients were examined with standard MR-sequences, coronal SWMR and radiographs in anteroposterior pelvic view. Coronal maximum intensity projection (MIP) images of both hips were automatically reconstructed on SWMR and T1weighted images. Sharp´s angle, Tönnis angle, lateral center-edge angle of Wiberg and caput-collum-diaphyseal angle were measured on coronal SWMR MIP-images, T1weighted MIP-images and radiographs. Measurements were compared by linear regression analysis and Bland-Altmann Plots, using radiographs as reference standard. Additionally, a ratio between the signal intensity of muscles and bone on SWMR and T1weighted MIP-images was calculated and compared between these two sequences. SWMR enables the reliable assessment of Sharp´s angle (SWMR: R2 = 0.80; T1weighted: R2 = 0.37), Tönnis angle (SWMR: R2 = 0.86; T1weighted: not measurable), lateral center-edge angle of Wiberg (SWMR: R2 = 0.88; T1weighted: R2 = 0.40) and caput-collum-diaphyseal angle (SWMR: R2 = 0.38; T1weighted: R2 = 0.18) compared to radiographs with a higher accuracy than conventional MR imaging. The ratio between the intensity of muscles and bone was significant higher on SWMR (2.00 and 2.02) than on T1weighted MIP-images (1.6 and 1.42; p < 0.001).

Intracellular accumulation capacity of gadoxetate: initial results for a novel biomarker of liver function.

Previous studies have shown gadoxetate disodium's potential to represent liver function by its retention in the hepatobiliary phase. Additionally, in cardiac imaging, quantitative characterization of altered parenchyma is established by extracellular volume (ECV) calculation with extracellular contrast agents. Therefore, the purpose of our study was to evaluate whether intracellular accumulation capacity (IAC) of gadoxetate disodium derived from ECV calculation provides added scientific value in terms of liver function compared to the established parameter reduction rate (RR). After local review board approval, 105 patients undergoing standard MR examination with gadoxetate disodium were included. Modified Look-Locker sequences were obtained before and 20 min after contrast agent administration. RR and IAC were calculated and correlated with serum albumin, as a marker of synthetic liver function. Correlation was higher between IAC and albumin, than between RR and albumin. Additionally, capacity of both RR and IAC to distinguish between patients with or without liver cirrhosis was investigated, and differed significantly in their respective means between patients with cirrhosis and those without. We concluded, that the formula to calculate ECV can be transferred to calculate IAC of gadoxetate disodium in hepatocytes, and, thereby, IAC may possibly qualify as an imaging-based parameter to estimate synthetic liver function.

Improved visualisation of hepatic metastases in gadoxetate disodium-enhanced MRI: Potential of contrast-optimised (phase-sensitive) inversion recovery imaging.

BACKGROUND: Detection of metastases can have a significant impact on therapy. Nevertheless, even in gadoxetate disodium-enhanced MR scans, very small hepatic metastases may be difficult to see. PURPOSE: To investigate the potential of a contrast-optimised (phase-sensitive) inversion recovery MR sequence in gadoxetate disodium-enhanced scans for detection of hepatic metastases. MATERIALS AND METHODS: With institutional review board approval and after written informed consent, 40 patients (18 male, 22 female) with suspected or known hepatic metastases were examined on a 1.5 T MR system. A T1-weighted gradient-echo volumetric-interpolated-breath-hold (VIBE) sequence was acquired as part of the standard imaging protocol 20 minutes after administration of gadoxetate disodium. Additionally, an IR sequence was acquired with an inversion time to suppress native signal from metastases. Overall image quality and delineation of lesions were assessed on VIBE as well as on magnitude-reconstructed (MAG) and phase-sensitive IR (PSIR) sequences. Lesion-to-liver contrast (LLC) was compared between VIBE and MAG images. RESULTS: Overall image quality was high in both VIBE and MAG IR sequences (VIBE 4.275; MAG 4.313), yet significantly lower in PSIR (4.038). Subjective delineation of lesions was higher on MAG and PSIR images compared to VIBE in all size groups with an overall statistically significant difference for VIBE vs. MAG vs. PSIR (p < .001) in the variance analysis. Mean LLC was 0.35±0.01 for VIBE sequences, and 0.73±0.01 for MAG. CONCLUSION: Contrast-optimised PSIR seems to improve imaging characteristics of hepatic metastases in gadoxetate disodium-enhanced scans compared to T1 gradient-echo VIBE sequences.

Feasibility of gadoxetate disodium enhanced 3D T1 MR cholangiography (MRC) with a specific inversion recovery prepulse for the assessment of the hepatobiliary system.

AIM: To compare the potential of a gadoxetate disodium enhanced navigator-triggered 3D T1 magnetic-resonance cholangiography (MRC) sequence with a specific inversion recovery prepulse to T2-weighted MRCP for assessment of the hepatobiliary system. MATERIALS AND METHODS: 30 patients (12 male, 18 female) prospectively underwent conventional navigator-triggered 3D turbo spin-echo T2-weighted MRCP and 3D T1 MRC with a specific inversion pulse to minimise signal from the liver 30 minutes after administration of gadoxetate disodium on a 1.5 T MRI system. For qualitative evaluation, biliary duct depiction was assessed segmentally following a 5-point Likert scale. Visualisation of hilar structures as well as image quality was recorded. Additionally, the extrahepatic bile ducts were assessed quantitatively by calculation of signal-to-noise ratios (SNR). RESULTS: The advantages of T1 3D MRC include reduced affection of image quality by bowel movement and robust depiction of the relative position of the extrahepatic bile ducts in relation to the portal vein and the duodenum compared to T2 MRCP. However, overall T1 3D MRC did not significantly (p > 0.05) improve the biliary duct depiction compared to T2 MRCP in all segments: Common bile duct 4.1 vs. 4.4, right hepatic duct 3.6 vs. 4.2, left hepatic duct 3.5 vs. 4.1. Image quality did not differ significantly (p > 0.05) between both sequences (3.6 vs. 3.5). SNR measurements for the hepatobiliary system did not differ significantly (p > 0.05) between navigator-triggered T1 3D MRC and T2 MRCP. CONCLUSIONS: This preliminary study demonstrates that T1 3D MRC of a specific inversion recovery prepulse has potential to complement T2 MRCP, especially for the evaluation of liver structures close to the hilum in the diagnostic work-up of the biliary system in patients receiving gadoxetate disodium.

Differences of airway dimensions between patients with and without bronchiolitis obliterans syndrome after lung transplantation-Computer-assisted quantification of computed tomography.

BACKGROUND: The aim of our retrospective study was to determine whether a dedicated software for assessment of airway morphology can detect differences in airway dimensions between patients with and without bronchiolitis obliterans syndrome (BOS), regarded as the clinical correlate of chronic lung allograft rejection. METHODS: 12 patients with and 14 patients without diagnosis of BOS were enrolled in the study. Evaluation of bronchial wall area percentage (WA%) and bronchial wall thickness (WT) in all follow-up CT scans was performed using a semiautomatic airway assessment tool. We assessed temporal changes (ΔWA%, ΔWT) and compared these morphological parameters with forced expiratory volume in one second (ΔFEV1). RESULTS: In patients with and without BOS, the temporal changes over the entire follow-up were 26.6% versus 16.2% for ΔFEV1 (p=0.034), 14.2% versus 5.4% for ΔWA% (p=0.003) and 0.212mm versus 0.064mm for ΔWT (p=0.011). CONCLUSIONS: We detected significant differences of the temporal changes of airway dimensions (ΔWA%, ΔWT) between lung transplant recipients with and without BOS. We conclude that computer-assisted bronchial wall measurements in CT scans might complement the information from pulmonary function tests and establish as a non-invasive method to confirm BOS in lung transplant recipients in the future.

Novel Dynamic Hepatic Magnetic Resonance Imaging Strategy Using Advanced Parallel Acquisition, Rhythmic Breath-Hold Technique, and Gadoxetate Disodium Enhancement.

OBJECTIVE: The aim of the study was to evaluate image quality of a dynamic hepatic magnetic resonance (MR) imaging strategy based on advanced parallel acquisition combined with rhythmic breath-hold and gadoxetate disodium enhancement. MATERIALS AND METHODS: Twenty-seven patients (21 male/6 female; mean age, 57.3 years) were enrolled in this institutional review board-approved study and underwent MR imaging at 3 T. The sequence (T1 3-dimensional gradient-recalled echo; acceleration factor, 4; reconstruction mode; controlled aliasing in parallel imaging resulting in higher acceleration factors; acquisition time, 10.4 seconds) was repeated at 8 fixed time points within the 3 minutes after contrast agent injection. Image quality was evaluated on a 5-point scale (1, excellent; 5, nondiagnostic). Dynamic sequences were classified according to perfusion phases and contrast characteristics. Artifacts and position of the liver in the z axis were recorded and analyzed. RESULTS: Overall image quality was found to be 1.44 (95% confidence interval, 1.18-1.71). Contrast was scored as excellent in 25 of 27 patients for central vessels and 22 of 27 patients for peripheral vessels. Adequate-quality arterial-phase images were obtained in all 27 patients. Double arterial and single arterial phases were acquired in 13 of 27 and 14 of 27 patients (n = 6 arterial dominant, n = 8 early arterial phases), respectively. In 1 (3.7%) of 27 patients, severe respiratory artifacts were seen during an early arterial phase. Artifacts were observed in 21 of 27 patients and rated as mild in 19 of these. Compromised quality was related to receiver coils (17 of 29), parallel imaging (6 of 29), breathing (3 of 29), and other causes (3 of 29). The position of the liver throughout the dynamic phases was highly constant, with a greatest mean shift of +2.9 mm throughout the first dynamic acquisition. CONCLUSIONS: Advanced parallel acquisition with rhythmic breath-hold and gadoxetate injection allows arterial phase imaging without breathing artifacts; a decelerated yet normal breathing pattern results in very robust breath-hold depth.