Michael D. Harpen

Sonographic determination of renal volumes in normal neonates

Renal diseases that affect renal size without altering renal architecture require a quantitative means of detection. A prospective study was undertaken to establish normal values for renal volumes in healthy neonates using sonography. Volumes were determined by two methods; (1) the serial area-volume method using parallel transverse images; and (2) the prolate ellipsoid model of the kidney using orthogonal diameters taken from ultrasound images. Renal volumes for both the right and left kidneys in both sexes were found to be approximately 10 ml. There was no significant difference between the results obtained by either method, nor were there significant differences between the volumes of the right and left kidneys within either sex. No difference in renal volume was noted between sexes. The mean greatest renal length was also computed for right and left kidneys in both sexes. Knowledge of normal renal volumes may aid in the diagnosis of urinary system disorders in neonates.

Sample noise with circular surface coils

Presented is a straightforward derivation of the effective sample resistance presented to the input amplifier of a nuclear magnetic resonance imager when flat circular surface coils are used to image lossy media. The resistance may be used to determine sample noise following the method of Hoult and Lauterbur.

Derivation of gamma variate indicator dilution function from simple convective dispersion model of blood flow

The gamma variate function, commonly used to analyze time-activity curves obtained in nuclear medicine flow studies, is shown to be related to the solution to the differential equation obtained from a one-dimensional convective dispersive model of blood flow.

Magnetic resonance and CT imaging correlated with clinical status in SSPE

Five patients afflicted with subacute sclerosing panencephalitis were studied with computed tomography and magnetic resonance imaging. Computed tomography documented changes of nonspecific cerebral atrophy and low attenuation in the subcortical white matter. Magnetic resonance imaging revealed bilateral, symmetric, and diffuse abnormal increased signal in the white matter of the cerebral hemispheres with normal posterior fossa structures in 4 of 5 patients. Magnetic resonance imaging was superior to computed tomography in demonstrating the total extent of abnormality and may be the imaging modality of choice for this childhood disease.

Positronium: Review of symmetry, conserved quantities and decay for the radiological physicist

The PET-CT scanner, which overlays a high spatial resolution CT image on a relatively low resolution physiologic PET image, has greatly increased the efficacy of the PET imaging modality. With the resulting increase in the presence of PET imaging in the radiologic and medical physics communities, medical physicists can expect professional responsibilities in acceptance testing, quality assurance, radiation safety and resident teaching of this new modality. With this in mind we present a review of a subtle aspect of PET: the formation, symmetry properties and decay of positronium; the hydrogen like positron-electron complex which forms prior to annihilation.

A simple theorem relating noise and patient dose in computed tomography.

Presented is a simple model describing the dependence of image noise in computed tomography on the x-ray beam profile. The model is used to derive the x-ray profile which minimizes total image noise at constant integral patient dose. The profile may be produced with a bow-tie-type beam shaping filter. Results of the analysis are validated using a computer simulation of computed tomography (CT) acquisition and reconstruction.

Magnetic resonance imaging in neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinosis is a group of neurodegenerative disorders characterized by accumulation of lipofuscin and/or ceroid within the tissues of the body. These entities are manifest by visual, intellectual, and motor deterioration as well as recurrent seizures. Computed tomography has been shown to demonstrate changes of cerebral atrophy in more severely affected patients. Seven patients with neuronal ceroid lipofuscinosis were examined with both computed tomography and magnetic resonance imaging, and the results were correlated with the clinical severity of the disorder. Two less severely affected patients had normal results on computed tomography and magnetic resonance imaging studies. Varying degrees of cerebral atrophy were seen in the remaining five patients with both computed tomography and magnetic resonance imaging. Severity of atrophy correlated with the severity of disability in these patients. Abnormal white matter was seen in the two most severely affected patients only with magnetic resonance imaging. Although the findings in patients with neuronal ceroid lipofuscinosis were nonspecific, the increased sensitivity of magnetic resonance imaging for subtle white matter abnormalities over computed tomography may prove helpful in monitoring the progression of this rare disorder.

Ethnic factors in the variability of primary vesico-ureteral reflux with age

Objective. To determine any ethnic difference in the rate of spontaneous decrease in the incidence of primary vesico-ureteral reflux (VUR). Materials and methods. Voiding cystourethrograms on 738 patients with urinary tract infection were reviewed, and the incidence of primary vesico-urethral reflux was correlated with age, gender and ethnic origin. Results. There was a gradual decrease in the incidence of primary VUR in whites between 0–10 years, while the incidence of primary VUR in blacks was very low and remained the same. After 10 years of age, no difference was present. Conclusion. The possibility of delayed maturation of the antireflux mechanism in whites is considered as a possible explanation, and the possibility of an ethnic basis for this is suggested.

An introduction to wavelet theory and application for the radiological physicist.

The wavelet transform, part of a rapidly advancing new area of mathematics, has become an important technique for image compression, noise suppression, and feature extraction. As a result, the radiological physicist can expect to be confronted with elements of wavelet theory as diagnostic radiology advances into teleradiology, PACS, and computer aided feature extraction and diagnosis. With this in mind we present a primer on wavelet theory geared specifically for the radiological physicist. The mathematical treatment is free of the details of mathematical rigor, which are found in most other treatments of the subject and which are of little interest to physicists, yet is sufficient to convey a reasonably deep working knowledge of wavelet theory.

Harmonic structure of cylindrical imaging coils

Presented is a derivation of an exact closed-form expression for the spectra of resonant frequencies for magnetic resonance imaging birdcage coils in the limit of long coils with many elements. Results of the analysis are compared with observation in a variety of birdcage coils where it is shown that for even relatively short coils the progression of resonant frequencies are of the form omega m = omega 1m +/- 1/2 + low pass; -high pass, with m integer and omega 1 the primary resonance.