Mark S. Rzeszotarski

The detection and quantification of retinopathy using digital angiograms

An algorithm is presented for the analysis and quantification of the vascular structures of the human retina. Information about retinal blood vessel morphology is used in grading the severity and progression of a number of diseases. These disease processes are typically followed over relatively long time courses, and subjective analysis of the sequential images dictates the appropriate therapy for these patients. In this research, retinal fluorescein angiograms are acquired digitally in a 1024x1024 16-b image format and are processed using an automated vessel tracking program to identify and quantitate stenotic and/or tortuous vessel segments. The algorithm relies on a matched filtering approach coupled with a priori knowledge about retinal vessel properties to automatically detect the vessel boundaries, track the midline of the vessel, and extract useful parameters of clinical interest. By modeling the vessel profile using Gaussian functions, improved estimates of vessel diameters are obtained over previous algorithms. An adaptive densitometric tracking technique based on local neighborhood information is also used to improve computational performance in regions where the vessel is relatively straight.

An MTF method immune to aliasing

The variance derived from the images of cyclic bar patterns can be used to determine the modulation transfer function (MTF) of an imaging system. Unlike most MTF methods, it is applicable even when the imaging system undersamples the test object and generates aliasing errors. The validity of the variance method in the presence of aliasing is established theoretically and by computer simulation.

The x‐ray fovea, a device for reducing x‐ray dose in fluoroscopy

The x-ray fovea (U.S. patents pending) is a device for reducing x-ray dose to patients and operations during x-ray fluoroscopy. It consists of a semitransparent collimator with an open, circular, central hole. The fovea collimator is placed at the exit of the x-ray tube, and the attenuation of the peripheral x-ray beam reduces x-ray exposure to patients and operators. The shadow caused by the x-ray fovea can be compensated using real-time image processing hardware. Accurate compensation is demonstrated for both linearly and logarithmically acquired images using a model that accounts for beam hardening in the fovea collimator. The central fovea region has improved image quality due to reduced scatter and veiling glare from the periphery. From beam-stop measurements, a 40% reduction in scatter plus veiling glare is measured using the fovea. A contrast improvement ratio of 1.5 is measured throughout the central region. In the compensated periphery, noise is increased by a factor of 1.66 because fewer photons are detected, but a small amount of temporal filtering compensates this degradation. The Roentgen area product (RAP) exposure to patients is reduced by approximately 70%, while scattered exposure to operators is reduced by approximately 60%.

Physics Instruction for Radiology Residents in the Era of the New ABR Examination Process

t o b 4 o m t w q p n ajor changes in the ABR certifiation process are being impleented, starting with the class of edical residents who began their adiology residencies in July 2010. he former 3-examination certifiation process (physics, clinical ritten, and oral) is being elimiated over the next few years and ill be replaced by a new 2-examiation computer-based certificaion process [1,2]. Oral examinaions will no longer occur. The first of hese 2 computer-based examinaions will be administered during the esidency, and the second will be adinistered 15 months after graduaion from the residency program. oth examinations will include asessments of physics knowledge esential to practicing radiologists, as ell the ABR’s Maintenance of ertification cognitive examinaions radiologists will take to demnstrate their competency throughut their careers.

Radiation exposure in extremely low birth weight infants during their neonatal intensive care unit stay

BackgroundExtremely low birth weight (ELBW <1000 g) infants may have increased sensitivity to radiation exposure. Our objective was to estimate the radiation exposure in survivors of ELBW infants during their neonatal intensive care unit (NICU) stay.MethodsIn this retrospective cohort study, medical records of all ELBW infants who had been admitted to our NICU between May 1999 and October 2009 were reviewed. The infants’ total entrance skin exposure [ESE in micro-Gray (μGy)] was estimated.ResultsAmong 450 survivors, the mean gestational age (GA) was 26.3±2.1 weeks, and the mean birth weight (BW) was 774.2±144.4 g. Infants received a median of 32 (range: 1–159) X-rays, with an estimated ESE of 1471 μGy (range: 28–9264). Total ESE was inversely proportional to GA (r=−0.34; P<0.01), and BW (r=−0.39; P=0.01) and proportional to the severity of illness [score for neonatal acute physiology-perinatal extension (SNAPPE), r=0.39; P=0.01]. In a linear regression analysis, GA, SNAPPE and necrotizing enterocolitis were associated with radiation exposure (ESE) in ELBW infants (r2=0.133; P<0.001).ConclusionsDuring their NICU stay, ELBW infants were subjected to a significant number of diagnostic X-ray procedures. Our data highlight the need to closely monitor the number of X-ray procedures ordered to ELBW infants to avoid unnecessary radiation exposure.

Localization of the nucleolar organizer by computer-aided analysis of a variant no. 21 in a human isolate

SummaryA variant chromosome no. 21 consisting of two stalks and two satellites in tandem was detected during a survey of a human isolate. The variant segregated in three generations of a large kindred. One male had the variant no. 21, a metacentric Y, and a 47, XXY complement; however, no other evidence of chromosomal nondisjunction was found. Computer-aided analysis of sequentially stained variant no. 21 chromosomes indicated that silver-stained material corresponded to the proximal stalk region (as defined defined by Giemsa). These data support the hypothesis that human nucleolar organizers are localized to the stalks of acrocentric chromosomes.

Introduction to two-dimensional Fourier analysis

The application of two-dimensional Fourier analysis provides new avenues for research in visual perception. This tutorial serves as an introduction to some of the methods used in two-dimensional Fourier analysis and an introduction to two-dimensional image processing in general.

Application of two-dimensional Fourier transforms to problems of visual perception

Neurophysiological and psychophysical evidence indicates that the visual system performs a sort of Fourier analysis of retinal variations in brightness through multiple spatial frequency-tuned channels. Two types of applications of techniques of two-dimensional Fourier analysis are discussed: (1) modeling and simulation of visual functions, and (2) generation of stimuli in which the spatial frequency information is controlled. Examples of both these applications are presented.