Image Post-processing Techniques Research Articles

A clinical MRI investigation of the relationship between kidney volume measurements and renal function in patients with renovascular disease

Recent improvements in MR image acquisition and post-processing techniques have allowed quantitative kidney volume measurements to be derived from patient studies. These morphological indices can provide "snapshot" assessments that may be related to kidney function. The study objective was to measure cortical and total kidney volumes in patients with renovascular disease (RVD) using contrast-enhanced MR angiography (CE-MRA) in order to assess the reproducibility of the technique and to investigate associations between volumes and renal function as measured by glomerular filtration rate (GFR) calculations. 50 patients with RVD were scanned using CE-MRA. Kidney lengths, volumes and renal artery stenoses (RAS) were evaluated, and GFR was calculated using clinical formulae and nuclear medicine isotope renography. Mean MRI kidney lengths were 10.3+/-0.2 cm, and mean MRI volumes were 74.9+/-3.6 cm3 (cortical) and 128.5+/-5.3 cm3 (total). Kidneys supplied by moderately stenosed arteries had enlarged lengths and volumes, whilst those supplied by severely stenosed arteries had significantly smaller lengths (p<0.001) and volumes (p<0.001). There was a clear association between MRI cortical volume and GFR (r = 0.74, p<0.001, n = 48), but less so between kidney length and GFR (r = 0.54, p<0.001, n = 48). For individual patients, left/right cortical volume differences were small provided that severe RAS was not present, but large left/right volume differences and a GFR reduction were noted when severe RAS was present. The cortical volume distribution provides a useful single-timepoint indication of kidney function as defined by GFR, with no additional data acquisition required other than that of standard CE-MRA examination.

CT diagnosis and staging of pancreatic carcinoma

The current use of multidector row helical CT (MDCT) and imaging postprocessing techniques represents an additional step forward in the use of helical CT for detection and staging of pancreatic carcinoma. Although no large series have been published detailing the accuracy of MDCT compared to single detector row helical CT, the additional resolution of the MDCT thin-section images and use of postprocessing techniques should certainly equal, if not exceed, the accuracy of the helical CT.

Morphological age-dependent development of the human carotid bifurcation

The unique morphology of the adult human carotid bifurcation and its sinus has been investigated extensively, but its long-term, age-dependent development has not. It is important fundamentally and clinically to understand the hemodynamics and developmental forces that play a role in remodeling of the carotid bifurcation and maturation of the sinus in association with brain maturation. This understanding can lead to better prognostication and therapy of carotid disease. We analyzed the change of sinus morphology and the angle of the carotid bifurcation in four postnatal developmental stages (Group I: 0–2 years, Group II: 3–9 years, Group III: 10–19 years, and Group IV: 20–36 years, respectively) using multiprojection digital subtraction angiograms and image post-processing techniques. The most significant findings are the substantial growth of the internal carotid artery (ICA) with age and the development of a carotid sinus at the root of the ICA during late adolescence. The bifurcation angle remains virtually unchanged from infancy to adulthood. However, the angle split between the ICA and external carotid artery (ECA) relative to the common carotid artery (CCA) undergoes significant changes. Initially, the ICA appears to emanate as a side branch. Later in life, to reduce hydraulic resistance in response to increased flow demand by the brain, the bifurcation is remodeled to a construct in which both daughter vessels are a skewed continuation of the parent artery. This study provides a new analysis method to examine the development of the human carotid bifurcation over the developmental years, despite the small and sparse database. A larger database will enable in the future a more extensive analysis such as gender or racial differences.

In vivo morphometry and functional analysis of human articular cartilage with quantitative magnetic resonance imaging--from image to data, from data to theory.

Analyses of form-function relationships and disease processes in human articular cartilage necessitate in vivo assessment of cartilage morphology and deformational behavior. MR imaging and advanced digital post-processing techniques have opened novel possibilities for quantitative analysis of cartilage morphology, structure, and function in health and disease. This article reviews work on three-dimensional post-processing of MR image data of articular cartilage, summarizing studies on the accuracy and precision of quantitative analyses in human joints. It presents normative values on cartilage volume, thickness, and joint surface areas in the human knee, and describes the correlation between different joints and joint surfaces as well as their association with gender, body dimensions, and age. The article summarizes ongoing work on functional adaptation of articular cartilage to mechanical loading, analyses of in situ cartilage deformation in intact joints in vivo and in vitro, and the quantitative evaluation of cartilage tissue loss in osteoarthritis. We describe evolving techniques for assessment of the structural/biochemical composition of articular cartilage, and discuss future perspectives of quantitative cartilage imaging in the context of joint mechanics, mechano-adaptation, epidemiology, and osteoarthritis research. Specifically, we show that fat-suppressed gradient echo sequences permit valid analysis of cartilage morphology, both in healthy and severely osteoarthritic joints, as well as highly reproducible measurements (CV%=1 to 3% in the knee, and 2 to 10% in the ankle). Relatively small differences in cartilage morphology exist between both limbs of the same person (approximately 5%), but large differences between individuals (CV% approximately 20%). Men display only slightly thicker cartilage then women (approximately 10%), but significantly larger joint surface areas (approximately 25%), even when accounting for differences in body weight and height. Weight and height represent relatively poor predictors of cartilage thickness (r2 <15%), but muscle cross section areas display more promising correlations (r2 >40%). The level of physical exercise (sportive activity) does not account for interindividual differences in cartilage thickness. The thickness appears to decrease slightly in the elderly--in particular in women, even in the absence of osteoarthritic cartilage lesions. Strenuous physical exercises (e.g., knee bends) cause a 6% patellar cartilage deformation in young individuals, but significantly less deformation in elderly men and women (<3%). The time required for full recovery after exercise (fluid flow back into the matrix) is relatively long (approximately 90 min). Static in situ compression of femoropatellar cartilage with 150% body weight produces large deformations after 4 h (approximately 30% volume change), but only very little deformation during the first minutes of loading. Quantitative analyses of magnetization transfer and proton density hold promise for biochemical evaluation of articular cartilage, and are shown to be related to the deformational behavior of the cartilage. Application of these techniques to larger cohorts of patients in epidemiological and clinical studies will establish the role of quantitative cartilage imaging not only in basic research on form-function relationships of articular cartilage, but also in clinical research and management of osteoarthritis.

Increased MR Image Contrast by Correlation of Tissue Relaxation Properties

An image postprocessing technique that is based on the relaxation properties of tissues and that can produce MR images with increased contrast is proposed. The technique involves no a priori assumptions concerning the form of the relaxation decay. An arbitrary number of postprocessed images, each emphasizing a selected tissue type, is obtained from the original images of a multiecho acquisition. It is shown with examples that the technique allows more complete utilization of relaxation information for tissue differentiation.

Widening the effective field of view of adaptive-optics telescopes by deconvolution from wave-front sensing: average and signal-to-noise ratio performance

A fundamental problem of adaptive-optics systems is the very narrow corrected field of view that can be obtained because turbulence is extended in altitude throughout the atmosphere. The correctable field of view is of the order of 5-10 µrad at visible wavelengths and increases as the wavelength increases. Previous concepts to broaden the corrected field of view have been hardware oriented, requiring multiple wave-front sensor (WFS) measurements to control multiple deformable mirrors. We analyze the average and the signal-to-noise-ratio performance of an image measurement and postprocessing technique that uses simultaneous measurements of a short-exposure compensated image measured in an off-axis direction; an additional WFS measurement is taken in the off-axis direction. Results are presented for infinite-altitude WFS beacons driving both the WFS for the adaptive optics and the WFS looking in the off-axis direction, a variety of seeing and WFS light-level conditions, and off-axis angles from two to six times the isoplanatic angle. This technique improves the average effective transfer function out to a field angle of at least six times the isoplanatic angle while providing a higher signal-to-noise ratio in the spatial frequency domain.