Automated computerized scheme for detection of unruptured intracranial aneurysms in three-dimensional magnetic resonance angiography

RATIONALE AND OBJECTIVES: A computerized scheme for automated detection of unruptured intracranial aneurysms in magnetic resonance angiography was developed based on the use of a three-dimensional selective enhancement filter for dots (aneurysms). MATERIALS AND METHODS: Twenty-nine cases with 36 unruptured aneurysms (diameter, 3 to 26 mm; mean, 6.6 mm) and 31 non-aneurysm cases were used in this study. The isotropic 3-dimensional magnetic resonance angiography images with 400 x 400 x 128 voxels (voxel size, 0.5 mm) were processed by use of the selective enhancement filter. The initial candidates were identified by use of a multiple gray-level thresholding technique on the dot-enhanced images and a region-growing technique with monitoring some image features. All candidates were classified into four types of candidates according to the size and local structures based on the effective diameter and skeleton image of each candidate (ie, large candidates and three types of small candidates including short-branch type, single-vessel type, and bifurcation type). In each group, a number of false-positives were removed by use of different rules on localized image features related to gray levels and morphology. Linear discriminant analysis was used for further removal of false-positives. RESULTS: With this computer-aided diagnostic scheme, all of 36 aneurysms were correctly detected with 2.4 false-positives per patient based on a leave-one-out-by-patient test method. CONCLUSION: This computer-aided diagnostic system would be useful in assisting radiologists for the detection of intracranial aneurysms in magnetic resonance angiography.     

Use of a standardized uptake value for parametric in vivo imaging of benzodiazepine receptor distribution on [<Superscript>11</Superscript>C]flumazenil brain PET

To simplify the acquisition protocol of carbon-11 labeled flumazenil (FMZ) positron emission tomography (PET) for distribution volume (DV) images, we attempted to obtain standardized uptake value (SUV) images compatible with DV images, and assessed the applicability of this method in patients with unilateral cerebrovascular diseases (CVD). [¹¹C]FMZ PET was performed in ten normal subjects. A DV image and ten sequential 5-min SUV images were generated for each subject. We investigated the correlation coefficient (r) and standard estimation of error (SEE) between the latter ten static images and the DV image using the pixel-by-pixel method, thereby determining the optimum acquisition phase. The same FMZ PET procedure was performed in 15 patients with unilateral CVD. Twenty regions of interest (ROIs) were positioned both in lesioned areas and in symmetrical regions. DV and SUV in the optimum phase for each ROI were calculated to compare the lesion-to-normal (L/N) ratio of DV and that of SUV. The highest r and a low SEE (r=0.957, SEE=633) were observed from 30 to 35 min after tracer administration in the study of normal subjects. A high r (0.945) and a low SEE (0.0438) between the DV L/N ratio and the SUV L/N ratio were obtained in the study of patients. Our study suggests that SUV images acquired from 30 to 35 min after FMZ administration are a suitable alternative to DV images not only in normal subjects but also in patients with unilateral CVD. This simple method seems to be valuable for the identification of altered neuronal activity in patients with CVD.     

Particle image velocimetry for flow analysis in longitudinal planes across a mechanical artificial heart valve

In the last decades a great number of in vitro studies have been conducted to improve the design and to understand the transvalvular flow patterns under steady-state and pulsating flow conditions. Steady-state tests are useful for studying the flow established upstream and downstream of the valve prosthesis in different flow conditions and, in particular, at the peak flow rate. In the present study, the particle image velocimetry (PIV) technique is employed to visualize the flow patterns in a precommercial model of a bi-leaflet mechanical heart valve prosthesis in a steady-state flow regime. The use of the PIV technique and a convenient test rig provide good conditions with which to investigate the whole flow field upstream and downstream of the valve. Velocity and vorticity maps are obtained for the flow passing through the prosthesis in different axial planes. A new and simple solution for the measurement test chamber is proposed. This innovative approach of observing the flow in staggered planes (other than diametrical planes) allows a flow analysis to be performed upstream and downstream of the valve in regions near the tube wall where it has the maximum potential for injury of the vessel's inner cell layer.     

Nephrogenic adenoma of the urinary bladder

Introduction: The nephrogenic adenoma (NA) is a benign metaplastic lesion of the urothelium and is attributed to chronic irritation of the mucosa, by injury, infection, stone disease or intravesical instrumentations. We present our experience on this morbid entity, its clinical appearance in the urinary bladder, its frequency and relapses. Furthermore we reviewed the related recent literature and focused on its potential to neoplastic degeneration and the value of the new diagnostic modalities. Patients and methods: Four patients with NA of the urinary bladder are presented. The papilloid or polypoid formations observed by the cystoscopy were identified after the TUR, as NA of the urinary bladder. Their mean follow-up was 3.5 years. Results: Remission of the symptoms was observed after TUR in all patients. Three out of four patients presented 1–7 relapses, while in one case, after seven NA relapses, a urothelial carcinoma of the bladder was diagnosed. Conclusions: Unlike histological features, the clinical – endoscopic characteristics of NA are non-specific. Even if it is not definitely considered like a premalignant condition, NA has to be followed up frequently and long lasting, because of its high recurrence rate. The combination of Cytology, Flow cytometry, DNA image analysis and Fluorescence in situ hybridisation of bladder washings or voided urine, are of high value in monitoring NA of the urothelium.     

Noquist: reduced field-of-view imaging by direct Fourier inversion.

A novel technique called "Noquist" is introduced for the acceleration of dynamic cardiac magnetic resonance imaging (CMRI). With the use of this technique, a more sparsely sampled dynamic image sequence is reconstructed correctly, without Nyquist foldover artifact. Unlike most other reduced field-of-view (rFOV) methods, Noquist does not rely on data substitution or temporal interpolation to reconstruct the dynamic image sequence. The proposed method reduces acquisition time in dynamic MRI scans by eliminating the data redundancy associated with static regions in the dynamic scene. A reduction of imaging time is achieved by a fraction asymptotically equal to the static fraction of the FOV, by omitting acquisition of an appropriate subset of phase-encoding views from a conventional equidistant Cartesian acquisition grid. The theory behind this method is presented along with sample reconstructions from real and simulated data. Noquist is compared with conventional cine imaging by retrospective selection of a reduced data set from a full-grid conventional image sequence. In addition, a comparison is presented, using real and simulated data, of our technique with an existing rFOV technique that uses temporal interpolation. The experimental results confirm the theory, and demonstrate that Noquist reduces scan time for cine MRI while fully preserving both spatial and temporal resolution, but at the cost of a reduced signal-to-noise ratio (SNR).     

The use of reference image criteria in X-ray diagnostics: an application for the optimisation of lumbar spine radiographs

To ensure that sufficient image quality is obtained in diagnostic radiology, the image quality of clinical radiographs has to be evaluated. We present two methods herein for evaluating antero-posterior (AP) radiographs of the lumbar spine. One was using image criteria, including six anatomical details (absolute method). In the other, the visibility of anatomical details relative to a reference radiograph was evaluated (visual grading analysis). In total, 14 technique groups were evaluated. The technique groups differed in tube voltage and detector system characteristics. Six different gradients of the H&D curves were simulated. The visual grading analysis showed larger differences in image quality compared with the absolute method. The influence on the image quality due to a variation in tube voltage was easier to detect than the influence on the image quality from the detector characteristics. The visibility of the anatomical details was significantly dependent on the location in the spine. The visual grading analysis was found to be the preferable evaluation method in studies such as the present; however, it is necessary to guide and train the observer before the evaluation is performed.     

Visual estimation of the global myocardial extent of hyperenhancement on delayed contrast-enhanced MRI

MRI with paramagnetic contrast agent allows the assessment of the extent of myocardial tissue injury after infarction. Visual segmental scoring has been widely used to define the transmural extent of myocardial infarction, but no attempt has been made to use visual scores in order to assess the percentage of the whole myocardium infarcted. By summing all the segmental scores using a 17-segment model, a global index of the size of the infarcted myocardium is easily obtained. The entire left ventricle of 60 patients with a recent myocardial infarction was scanned using an ECG-gated gradient echo sequence after injection of gadolinium contrast agent. The global score was defined as the sum of the scores on each segment, and expressed as a percentage of the maximum possible score. This index was compared with a planimetric evaluation of hyperenhancement, expressed as a percentage of the left ventricle myocardial volume. There is a good correlation between the two methods (r=0.91; y=1.06x+0.20), and the Bland-Altman plot shows a high concordance between the two approaches (mean of the differences =1.45%). A visual approach based on a 17-segment model can be used to evaluate the global myocardial extent of the hyperenhancement with similar results to planimetry.     

Late-arterial and portal-venous phase imaging of the liver with a multislice CT scanner in patients without circulatory disturbances: automatic bolus tracking or empirical scan delay?

The value of automatic bolus tracking in late-arterial and portal-venous phase imaging of the liver with a multislice CT scanner as compared with fixed time-delay examination in patients without circulatory disturbances is evaluated. For the evaluation of known or suspected liver disease, 98 multiphase contrast-enhanced CT examinations including double late-arterial phase imaging were randomized into either scanning with a scan delay of 30 s from the beginning of contrast material injection or scanning with automatic bolus tracking. Contrast material was injected at 0.07 ml/kg body weight/s over 30 s. Contrast enhancement in each acquisition was measured in the aorta, portal vein, liver, pancreas and hepatocellular carcinomas. The density difference between hepatocellular carcinomas and the hepatic parenchyma was calculated. The mean time to the first-pass acquisition as determined by automatic bolus tracking was 29.6 s. No statistically significant difference was observed between the two groups either in any enhancement in any acquisition or in the lesion-to-liver density difference. The use of automatic bolus tracking in late-arterial and portal-venous phase hepatic CT does not significantly improve the degree of contrast enhancement in the aorta, portal vein, liver and pancreas or lesion-to-liver conspicuity in patients without circulatory disturbances.     

Imaging the lymphatic system: possibilities and clinical applications

The lymphatic system is anatomically complex and difficult to image. Lymph ducts are responsible for the drainage of part of the bodys interstitial fluid. Lymph nodes account for the enrichment of lymph fluid, and can be involved in a large variety of diseases, especially cancer. For a long time, lymphatic imaging was limited to the sole use of conventional lymphography involving invasive procedures and patient discomfort. New contrast agents and techniques in ultrasound, nuclear medicine, and MR imaging are now available for imaging of both the lymphatic vessels and the lymph nodes. The objective of this review is to discuss the different imaging modalities of the lymphatic system, with a special focus on the new possibilities of lymphatic imaging including enhanced MR lymphography, sentinel node and positron emission tomography imaging, and contrast-enhanced ultrasound.     

Functional magnetic resonance imaging for neurosurgical planning in neurooncology

Functional magnetic resonance imaging (fMRI) is a non-invasive technique that is widely available and can be used to determine the spatial relationships between tumor tissue and eloquent brain areas. Within certain limits, this functional information can be applied in the field of neurosurgery as a pre-operative mapping tool to minimize damage to eloquent brain areas. In this article, we review the literature on the use of fMRI for neurosurgical planning. The issues addressed are: (1) stimulation paradigms, (2) the influence of tumors on the blood oxygenation level-dependent (BOLD) signal, (3) post-processing the fMRI time course, (4) integration of fMRI results into neuronavigation systems, (5) the accuracy of fMRI and (6) fMRI compared to intra-operative mapping (IOM).