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Biomedical subjects

F Kelcz

Publications and source records attributed to F Kelcz.

8 recordsLinked to original sources
PubMed1992

Sonography of renal transplants in dogs: the effect of acute tubular necrosis, cyclosporine nephrotoxicity, and acute rejection on resistive index and renal length.

Results of studies on the accuracy of the resistive index as a predictor of acute renal transplant rejection have varied widely. Clinical evaluations are limited by the inability to control the numerous coincidental factors that affect vascular resistance. We performed a controlled study in dogs to isolate the effects of acute tubular necrosis, cyclosporine toxicity, and acute rejection on the resistive index, and to compare them with a population of normal control subjects. By doing so, we hoped to identify the patterns of change in the resistive index over time and possibly explain the wide spectrum of resistive index data reported in the literature. Resistive index, a parameter calculated from relative systolic and diastolic velocity, indicates parenchymal resistance to perfusion. Since an increase in renal length also has been reported useful in predicting rejection, we studied changes in length in each of the isolated conditions. The normal control group (four dogs) had heterotopic autotransplantation with minimal cold ischemic time. The acute tubular necrosis group (six dogs) had heterotopic autotransplantation with 1 hr of warm ischemic time. The cyclosporine toxicity group (four dogs) was allowed approximately 3 months to heal from heterotopic autotransplantation. Very high (toxic) doses of cyclosporine were then administered. The acute rejection group (five dogs) had heterotopic allografting with minimal cold ischemic time. No medications were administered. In all groups, the abnormalities induced were confirmed by biopsy. Creatinine levels were also used to monitor cyclosporine toxicity. In the normal control and acute tubular necrosis groups, resistive index increased immediately after surgery, returning to baseline within 10 days. Renal length increased slightly in both groups, but the duration of increase was longer in the acute tubular necrosis group. No significant change in resistive index or renal length was seen in the cyclosporine toxicity group. In the acute rejection group, an initial decrease in resistive index during the mild to moderate phase was followed by a rapidly progressive increase with worsening rejection. Renal length increased progressively beginning immediately after surgery. Our study determined the patterns of change in resistance and renal length over time as caused by the isolated pathologic states. Our finding that vascular resistance decreased in mild to moderate acute rejection was unexpected, since almost all the literature reports resistive index elevation. This may explain some of the conflicting results obtained in Doppler investigations of rejection. Our results on renal length reinforce the positive clinical reports of its predictive value in rejection.

Animals↗
PubMed1992

Ultrasonographic evaluation of renal transplantation.

Ultrasonography of the renal transplant is still a key screening examination for transplant dysfunction. The addition of Doppler technology has permitted screening for hemodynamic alterations. Ambitious researchers predicted that these hemodynamic profiles would permit the differentiation of rejection from other complicating factors; however, recent research and clinical experience has shown this to be ineffective. Imaging identification of a dilated collecting system identifies the patient population that should undergo a Whitaker procedure. Identification of large or increasing fluid collections helps focus attention to possible hemorrhage or urine leak. Similarly, the ultrasonographic identification of a lymphocele as the cause of leg edema or hydronephrosis rapidly focuses surgical treatment. Doppler evaluation of hemodynamics must be performed on all renal transplant recipients. Although the role of the resistive index in predicting rejection has been minimized lately, numerous vascular complications, if untreated, would result in loss of the kidney. Doppler sonography identifies those patients who would benefit most from renal arteriography. The evaluation of renal morphology on the basis of ultrasonography alone has little role in predicting the cause of transplant dysfunction. We continue to evaluate renal size and to correlate it with the clinical presentation as well as resistive index to defer patients from biopsy if a more obvious cause of dysfunction is identified.

Humans↗
PubMed1991

MRI of the pancreas transplant: lack of correlation between imaging and clinical status.

Twenty-five MRI scans were performed on 14 patients with cadaveric pancreatic transplants to determine the role of this modality in the evaluation of transplant dysfunction. Our population included 12 normal transplants and 13 recipients with pancreatic graft dysfunction (either rejection or pancreatitis). Six of the latter patients had two or more scans permitting reassessment of the same transplant in various states of health. T1-and T2-weighted MR images were evaluated qualitatively and quantitatively to see if certain patterns were associated with clinical status. We found that although MRI was capable of producing excellent images of the in situ pancreatic transplant, this modality was unable to reliably distinguish the normal from the abnormal transplant. This conclusion differs from prior assessments; possible reasons for this are discussed.

Graft Rejection↗
PubMed1978

Computed tomographic measurement of the xenon brain-blood partition coefficient and implications for regional cerebral blood flow: a preliminary report.

The calculation of regional cerebral blood flow requires, in addition to the measurement of the clearance, a knowledge of the regional brain-blood partition coefficient. The usual 133Xe washout techniques do not measure this latter parameter but use published values for normal brain tissue. This may lead to large errors in pathological tissue because the partition coefficient changes significantly in brain tumors. Investigations have begun into the use of CT and stable xenon to produce a cross sectional view of the brain in terms of its brain-blood partition coefficients. Results of experiments using an iodine phantom and xenon inhalation in animals are presented.

Animals↗
PubMedDate not supplied

Absorption-edge fluoroscopy using a three-spectrum technique.

We have recently reported on a 1-kVp, two-filter image subtraction method for visualizing low concentrations of elements like iodine which have K-shell absorption edges in the diagnostic x-ray energy range. However, in the application of this technique to human thyroid imaging, superimposed images due to variations in tissue and bone thickness presented serious difficulties. In this paper, a technique is described for implementing a 3-kVp, three-filter approach. Using carefully chosen spectra and logarithmic image processing, images are produced which are compatible with our previously described two-stage storage-tube subtraction device. Proper manipulation of the resulting difference images results in a final absorption-edge image in which only the element of interest is visualized, with unwanted background images suppressed. Computer calculations are presented to illustrate the relative sizes of difference signals arising from the element of interest and from tissue and bone backgrounds. Phantom studies using iodine concentrations as small as 1 mg/cm2, with variations of 10 cm of tissue and 2 g/cm2 of bone, suggest that the theory is sound and that, with straightforward apparatus modifications, images of good quality should be possible.

Fluoroscopy↗
PubMedDate not supplied

Spectral considerations for absorption-edge fluoroscopy.

In our previous reports on absorption-edge fluoroscopy, it was not possible to relate fully the subtleties involved in the selection of spectral parameters. This paper is intended as an overview of this important aspect of the technique. It is shown that, by using the 1-kVp, 2-filter technique, it is possible to image certain elements (e.g., iodine and xenon) in the presence of tissue variations of +/-2 cm about the thickness at which perfect tissue cancellation takes place. Use of logarithmic signal processing extends this range, but bone thickness variations may not be accomodated because only two x-ray energies are involved in the imaging process. Use of a 3-kVp, 3-filter technique with logarithmic signal processing is shown to solve this problem. Computer simulations show that 1-mg/cm2 iodine may be imaged in the presence of 10 cm or more tissue variations and 2000-mg/cm2 bone variations.

Bone and Bones↗
PubMedDate not supplied

Noise considerations in dual energy CT scanning.

Dual energy CT scanning (tomochemistry) has been proposed as a method for determining various parameters relating to the elemental composition of the tissues. In this paper, our aim is to study the relative noise inherent in two proposed techniques for dual energy scanning; a "two crystal" technique and a "two kV" technique. In the two crystal technique, a split crystal detector is used to simultaneously obtain the high and low energy data during one scan at high kV. The two kV technique requires two scans taken with widely different kV settings. We first review three commonly used approaches for utilizing the scan data to compute the relevant parameters. A theoretical formalism is constructed which aids in understanding these methods. Then this formalism is used to study the influence of CT image noise on measurement precision in the case where the unknown parameters are densities. It is shown that, (1) the unavoidable overlap in the spectral data obtained by the two crystal technique results in a much lower signal-to-noise ratio than can be obtained by using the two kV technique, (2) the necessity for hard filtration of the high energy beam in the two kV technique has not heretofore been appreciated, and (3) the dose for a given x-ray tube heat load is also lower with the two kV technique.

Body Composition↗