Reducing ghosting due to k-space discontinuities in fast spin echo (FSE) imaging by a new combination of k-space ordering and parallel imaging

In multi-echo imaging sequences like fast spin echo (FSE), the point spread function (PSF) in the phase encoding direction contains significant secondary peaks (sidebands). This is due to discontinuities in adjacent k-space data obtained at different echo times caused by T₂ decay, and leads to ghosting and hence reduced image quality. Recently, utilising multiple coils for signal reception has become the standard configuration for MR systems due to the additional flexibility that parallel imaging (PI) methods can provide. PI methods generally obtain more data than is required to reconstruct an image. Here, this redundancy in information is exploited to reduce discontinuity-related ghosting in FSE imaging. Adjacent phase encoded k-space lines are acquired at different echo times alternately in the regions of discontinuity (called ‘feathering’). This moves the resulting ghost artefacts to the edges of the field of view. This property of the ghost then makes them amenable to removal using PI methods. With ‘feathered’ array coil data it is possible to reconstruct data over the region of the discontinuity from both echo times. By combining this data, a significant reduction in ghosting can be achieved. We show this approach to be effective through simulated and acquired MRI data.     

A three-dimensional physical model of MRI noise based on current noise sources in a conductor

Magnetic flux noise is generated by any conductor in equilibrium with a bath as a result of random fluctuating currents. A physical model of this flux noise is proposed, based on allowable current patterns in the conductor, which we describe as natural current modes. This model gives insight into the spatial characteristics of the magnetic noise which is encountered in a variety of magnetic measurements and imaging modalities such as magnetic resonance imaging (MRI).     

Cardiac lipoma: Six-year follow-up with MRI characteristics, and a review of the literature

A total of 63 cardiac lipomas have been reported to date. Although most of these rare tumors cause no symptoms, a few can have a detrimental effect on myocardial function as well as displacing and encasing the coronary arteries. This case of a cardiac lipoma was initially seen in 1982. The lipoma was found to be nonresectable at surgery due to involvement of the coronary arteries. This neoplasm was characterized with magnetic resonance imaging in 1989 on a follow-up visit. Magnetic resonance imaging is shown to be superior to computed tomography for identifying the relationship of the lipoma to the coronary arteries. This is a significant factor in determining resectability.     

Novel methodology for 3D reconstruction of carotid arteries and plaque characterization based upon magnetic resonance imaging carotid angiography data

In this study, we present a novel methodology that allows reliable segmentation of the magnetic resonance images (MRIs) for accurate fully automated three-dimensional (3D) reconstruction of the carotid arteries and semiautomated characterization of plaque type. Our approach uses active contours to detect the luminal borders in the time-of-flight images and the outer vessel wall borders in the T(1)-weighted images. The methodology incorporates the connecting components theory for the automated identification of the bifurcation region and a knowledge-based algorithm for the accurate characterization of the plaque components. The proposed segmentation method was validated in randomly selected MRI frames analyzed offline by two expert observers. The interobserver variability of the method for the lumen and outer vessel wall was -1.60%±6.70% and 0.56%±6.28%, respectively, while the Williams Index for all metrics was close to unity. The methodology implemented to identify the composition of the plaque was also validated in 591 images acquired from 24 patients. The obtained Cohen's k was 0.68 (0.60-0.76) for lipid plaques, while the time needed to process an MRI sequence for 3D reconstruction was only 30 s. The obtained results indicate that the proposed methodology allows reliable and automated detection of the luminal and vessel wall borders and fast and accurate characterization of plaque type in carotid MRI sequences. These features render the currently presented methodology a useful tool in the clinical and research arena.     

Influence of a parallel magnetic field on microwave-induced zero-resistance states and magnetoplasmon resonance

In an ultra-clean two-dimensional electron system (2DES), we have observed the magnetoplasmon resonance (MPR) through its microwave-photoconductivity, concurrently with the microwave-induced resistance oscillations (MIRO) and zero-resistance states (ZRS). It is found that the MIRO/ZRS is strongly suppressed by a moderate magnetic field () parallel to the 2DES, while the MPR is robust against a parallel magnetic field. These findings have not been addressed by current models proposed to explain the MIRO/ZRS.     

Comparison of accuracy of intravoxel incoherent motion and apparent diffusion coefficient techniques for predicting malignancy of head and neck tumors using half-Fourier single-shot turbo spin-echo diffusion-weighted imaging

Purpose

To evaluate the use of the intravoxel incoherent motion (IVIM) technique in half-Fourier single-shot turbo spin-echo (HASTE) diffusion-weighted imaging (DWI), and to compare its accuracy to that of apparent diffusion coefficient (ADC) to predict malignancy in head and neck tumors.

Patients and methods

HASTE DW images of 33 patients with head and neck tumors (10 benign and 23 malignant) were evaluated. Using the IVIM technique, parameters (D, true diffusion coefficient; f, perfusion fraction; D*, pseudodiffusion coefficient) were calculated for each tumor. ADC values were measured over a range of b values from 0 to 1000 s/mm². IVIM parameters and ADC values in benign and malignant tumors were compared using Student's t test, receiver operating characteristics (ROC) analysis, and multivariate logistic regression modeling.

Results

Mean ADC and D values of malignant tumors were significantly lower than those of benign tumors (P < 0.05). Mean D* values of malignant tumors were significantly higher than those of benign tumors (P < 0.05). There was no significant difference in mean f values between malignant and benign tumors (P > 0.05). The technique of combining D and D* was the best for predicting malignancy; accuracy for this model was higher than that for ADC.

Conclusions

The IVIM technique may be applied in HASTE DWI as a diagnostic tool to predict malignancy in head and neck masses. The use of D and D* in combination increases the diagnostic accuracy in comparison with ADC.     

Pattern-recognition system,designed on GPU,for discriminating between injured normal and pathological knee cartilage

The aim was to design a pattern-recognition (PR) system for discriminating between normal and pathological knee articular cartilage of the medial femoral (MFC) and tibial condyles (MTC). The data set comprised segmented regions of interest (ROIs) from coronal and sagittal 3-T magnetic resonance images of the MFC and MTC cartilage of young patients, 28 with abnormality-free knee and 16 with pathological findings. The PR system was designed employing the probabilistic neural network classifier, textural features from the segmented ROIs and the leave-one-out evaluation method, while the PR system's precision to “unseen” data was assessed by employing the external cross-validation method. Optimal system design was accomplished on a consumer graphics processing unit (GPU) using Compute Unified Device Architecture parallel programming. PR system design on the GPU required about 3.5 min against 15 h on a CPU-based system. Highest classification accuracies for the MFC and MTC cartilages were 93.2% and 95.5%, and accuracies to “unseen” data were 89% and 86%, respectively. The proposed PR system is housed in a PC, equipped with a consumer GPU, and it may be easily retrained when new verified data are incorporated in its repository and may be of value as a second-opinion tool in a clinical environment.     

Diet and gastrointestinal signal on T1-weighted magnetic resonance imaging of mice

In magnetic resonance (MR) imaging of small animals, the gastrointestinal contents may give rise to intense signals on T1-weighted images. The aim of this study was to determine the optimal dietary preparation to reduce gastrointestinal signals in mice and to evaluate the usefulness of this approach. Images of the mouse trunk were obtained using a T1-weighted, three-dimensional fast low-angle shot sequence under various dietary conditions and were compared with respect to the gastrointestinal signals and image quality. The dietary preparation studied included giving alternative diets for 24 h, intestinal cleansing, and 6-h fasting. Mice with and without dietary preparation underwent MR lymphography using gadofluorine 8, and the visualization of abdominal lymph nodes was compared. In the absence of dietary preparation, hyperintense areas were conspicuous in the gastrointestinal system, whereas on the images taken from mice fed potato or sweet potato for 24 h before imaging, gastrointestinal hyperintensity was less prominent. This preparation also reduced artifactual signals and resulted in higher-quality images of the kidneys. Intestinal cleansing, which consisted of 24-h fasting and laxative intake, did not reduce the gastrointestinal signals and caused signal changes that were indicative of fatty liver development. Some of the abdominal lymph nodes of the mice that did not receive dietary preparation were visualized on MR lymphography source images but not on maximum intensity projection (MIP) images. In contrast, on the MIP images of mice fed potato, all the lymph nodes delineated on the source images were successfully visualized. In conclusion, feeding mice potato or sweet potato for 24 h before MR imaging reduces the gastrointestinal signals and image degradation due to artifacts. Appropriate dietary preparations facilitate the display of target structures on MIP images and are expected to enhance the capabilities of small animal MR imaging.     

Structural effect on degradability and in vivo contrast enhancement of polydisulfide Gd(III) complexes as biodegradable macromolecular MRI contrast agents

The structural effect of biodegradable macromolecular magnetic resonance imaging (MRI) contrast agents, polydisulfide gadolinium (Gd)(III) chelates, on their in vitro degradability, and cardiovascular and tumor imaging were evaluated in mice. Polydisulfide Gd(III) chelates, Gd-DTPA cystamine copolymers (GDCC), Gd-DTPA l-cystine copolymers (GDCP), Gd-DTPA d-cystine copolymers (dGDCP) and Gd-DTPA glutathione (oxidized) copolymers (GDGP), with different sizes and narrow molecular weight distribution were prepared and evaluated both in vitro and in vivo in mice bearing MDA-MB-231 tumor xenografts. GDGP with large steric hindrance around the disulfide bonds had greater T(1) and T(2) relaxivities than GDCC, GDCP and dGDCP. The degradability of the polydisulfide by the endogenous thiols decreased with increasing steric effects around the disulfide bonds in the order of GDCC>GDCP, dGDCP>GDGP. The size and degradability of the contrast agents had a significant impact on vascular contrast enhancement kinetics. The agents with a large size and low degradability resulted in more prolonged vascular enhancement than the agents with a small size and high degradability. It seems that the size and degradability of the agents did not significantly affect tumor enhancement. All agents resulted in significant contrast enhancement in tumor tissue. This study has demonstrated that the vascular enhancement kinetics of the polydisulfide MRI contrast agents can be controlled by their sizes and structures. The polydisulfide Gd(III) chelates are promising biodegradable macromolecular MRI contrast agents for magnetic resonance angiography and cancer imaging.     

Influence of tube voltage and current on in-line phase contrast imaging using a microfocus x-ray source

In-line x-ray phase contrast imaging has attracted much attention due to two major advantages: its effectiveness in imaging weakly absorbing materials, and the simplicity of its facilities. In this paper a comprehensive theory based on Wigner distribution developed by Wu and Liu [Med. Phys. 31 2378-2384 (2004)] is reviewed. The influence of x-ray source and detector on the image is discussed. Experiments using a microfocus x-ray source and a CCD detector are conducted, which show the role of two key factors on imaging: the tube voltage and tube current. High tube current and moderate tube voltage are suggested for imaging.     

The combined effect of hypertension and type 2 diabetes mellitus on aortic stiffness and endothelial dysfunction: An integrated study with high-resolution MRI

Purpose

The purpose of this study was to investigate the combined effect of hypertension and type 2 diabetes mellitus (DM2) on aortic stiffness and endothelial dysfunction by using an integrated MRI approach.

Materials and Methods

A total of 31 non-hypertensive DM2 patients and 31 hypertensive DM2 patients underwent 3.0-T MRI. Aortic distensibility (AD), pulse wave velocity (PWV) and brachial artery flow-mediated dilation (FMD) were assessed. Student's t-test, Mann–Whitney U test, chi-squared test, Pearson correlation analysis, and univariable and multiple linear regression analyses were used for statistical analyses.

Results

The hypertensive patients showed lower AD at multiple levels (ascending aorta [AA]: 2.07 ± 0.98 × 10^− 3 mm Hg^− 1 vs. 3.21 ± 1.70 × 10^− 3 mm Hg^− 1, p < 0.01; proximal thoracic descending aorta [PDA]: 2.58 ± 0.72 × 10^− 3 mm Hg^− 1 vs. 3.58 ± 1.47 × 10^− 3 mm Hg^− 1, p < 0.01; distal descending aorta [DDA]: 3.11 ± 1.84 × 10^− 3 mm Hg^− 1 vs. 4.27 ± 1.75 × 10^− 3 mm Hg^− 1, p < 0.01); faster PWV (7.46 ± 2.28 m/s vs. 5.82 ± 1.12 m/s, p < 0.05) and lower FMD (12.67% ± 6.49% vs. 20.66% ± 9.7%; p < 0.01). Systolic blood pressure was an independent predictor of PWV, AA-AD, DDA-AD and FMD. FMD was statistically significantly associated with PWV (r = − 0.37, p < 0.01) and AD (p < 0.01).

Conclusions

Hypertension has a contributive effect on aortic stiffness and endothelial dysfunction in DM2 patients.     

Osteomyelitis: Sensitivity of 0.064 T MRI, three-phase bone scanning and indium scanning with biopsy proof

We compared the ability of magnetic resonance imaging (MRI) using a 0.064 T permanent magnet, three-phase bone scanning, and indium-labeled white blood cell (¹¹¹In-WBC) scanning, to diagnose osteomyelitis. Twenty-three patients underwent biopsy. All patients were examined at presentation with all three modalities. Sensitivities for each modality were calculated using biopsy as a gold standard. The results were 72% for MRI, 68% for bone scan, and 45% for ¹¹¹In-WBC. Specificities were not calculated because of lack of negative biopsies. MRI was as sensitive as bone scanning in the diagnosis of osteomyelitis. All modalities had lower than previously reported sensitivities for imaging osteomyelitis.