A precise receptor-positioning device for subtraction radiography, based on cross-arch stabilization.

OBJECTIVES: To devise and test for reproducibility a new patient-beam alignment device for subtraction radiography. METHODS: A rigid, cross-arch bar was used with bite-registration material. A modified Rinn XCP rod and ring were firmly attached to the bar and were placed in contact with the X-ray cone. The receptor was held by a slot in the bar. Duplicate sets (n=8 pairs) of digital radiographs were made with a modified, calibrated DenOptix photostimulable phosphor system. Image pairs were registered and compared for geometrical and intensity errors by means of quantitative subtraction radiography. The reproducibility of patient-beam alignment for each pair was determined by measuring spatial errors at alveolar crest edges and by comparing magnifications. Intensity errors measured at two predetermined regions of alveolar bone were used to estimate corresponding bone-mass errors. RESULTS: Misalignment at the alveolar crest was generally <1 pixel (0.085 mm), and everywhere < or =0.25 mm. The magnification was constant within a relative standard deviation of 0.13% (n=8). Trabecular features were generally invisible or barely visible in subtraction images. The standard deviation of intensity errors was 1.07% (n=16). This corresponds to a change in bone mass of approximately 2% or less. CONCLUSION: The device has potential for clinical population studies in which the goal is to detect small changes in bone mass and alveolar-crest height. It is convenient to use and comfortable for patients. Because of the cross-arch design, patient-beam alignment is expected to be relatively insensitive to bite-registration errors, tooth movement, and tooth loss.

Precise image-receptor calibration and monitoring of beam quality with a step wedge.

OBJECTIVE: To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality. METHODS: Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source. RESULTS: The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential. CONCLUSIONS: The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.

Quantitative dental radiography with a new photostimulable phosphor system.

OBJECTIVE: The purposes of this report are to present a quantitative model for digital oral radiography and to evaluate a new photostimulable phosphor system for bone mass measurements. STUDY DESIGN: Noise, linearity, and precision were measured from stepwedge images and blank images through use of a special least-squares calibration method. The model was used to estimate lower limits of detection for observing small changes in bone mineral content. RESULTS: The response was virtually linear, and the noise level of 2% to 3% is less than that of digitized film images. The precision of measurements averaged over a region of interest was generally better than 0.5%. CONCLUSIONS: If the scatter fraction is measured for each patient, bone loss can be measured by using only extraoral standards. Assuming a scatter fraction of 50% and considering only instrumental errors, the detection limit is <0.02 g/cm(2) for large image areas (> or =7 mm(2)) and <0.3 mg over areas of 1 mm(2) or smaller.

Dental photostimulable phosphor radiography.

Photostimulable phosphor radiography (PPR), a mature industry in medical imaging, became available in dentistry in 1994. At least three dental PPR systems have been made available commercially since that time. Although dental PPR offers a number of advantages over film-based methods, some aspects of dental PPR need improvement. Further research is needed to more fully compare and contrast this modality with film-based methods.

Successful treatment of renal allograft rejection in the presence of cytomegalovirus disease. A report of two cases.

We report 2 patients who developed cytomegalovirus (CMV) infection following renal transplantation. Both patients were treated with 9-(1,3-dihydroxy-2-propoxymethyl) guanine (ganciclovir). In the presence of CMV disease, both patients also had progressive elevations of the serum creatinine, which were attributed to graft rejection. Antirejection therapy was administered, with OKT3 in one case and pulse methylprednisolone in the other. Renal function improved in both patients, and CMV disease abated. These cases unique because antirejection therapy was instituted in the presence of documented CMV disease, without adverse sequelae. We believe that the administration of ganciclovir lessened the severity of CMV infection, while allowing the rejection episodes to be aggressively treated.

Role of class II HLA in cadaveric renal transplantation: a recent update.

Class II HLA matching, especially HLA-DQ and DR, significantly improved allograft survival. HLA-DQ and DR matching may also be associated, in general, with a quiescent posttransplantation course, reduced incidence of SRRE, and somewhat better response to OKT3 rescue therapy. We conclude that the matching of class II HLA remains an important predictor of transplant outcome in CyA-treated patients and should form the primary basis of organ sharing.

Long-term patient and renal allograft survival in HBsAg infection: a recent update.

Although the risk of HBsAg infection has now been reduced significantly by screening of blood, isolation of HBsAg+ patients, and more recently by vaccination, transplant-eligible patients can still be seen. We observed an increased mortality in HBsAg+ patients during 5 to 10 years posttransplantation. However, this could not be attributed to liver disease or dysfunction. Increased mortality and morbidity due to liver disease or dysfunction 10 years posttransplantation suggest that the HBsAg+ patients remain at a higher risk for developing liver disease during that period. In our study, HBsAg+ patients had a 10-year posttransplantation period relatively free of serious liver disease or dysfunction. Furthermore, both HBsAg+ and HBsAg- patients had a similar long-term allograft survival. It is unknown how the use of cyclosporine will affect those survival statistics. We, therefore, believe that HBsAg positivity per se should not constitute an absolute contraindication to transplantation.

Role of class I and class II HLA antigens in cadaveric renal transplantation.

HLA matching at MT and DQ appears to be an important predictor of allograft survival. Allografts with no MM at MT and DQ have a good outcome while a known MM at MT and DQ appears to be associated with poor allograft outcome. Thus, our priority should be to avoid an MM for these broad-reacting specificities and then to minimize incompatibilities at DR and HLA-B. Furthermore, our data indicate that allografts with MM at DQ and two MMs at HLA-B appear to be at a higher risk. Perhaps these latter transplants should not be performed with conventional immunosuppressive therapy.

Hepatitis B surface antigen (HBsAg) infection in a hemodialysis unit. II. Factors affecting host immune response to HBsAg.

Serum from 86 hemodialysis patients, 105 healthy hospital staff "at risk" and 160 regular hospital staff was screened for hepatitis B surface antigen (HBsAg) and antibody (anti-HBs). The combined prevalence of HBsAg and anti-HBs was higher in the staff of the artificial kidney unit (57.7%) than in the hemodialysis patients (33.7%). The healthy subjects with HBsAg infection responded significantly more often by producing anti-HBs compared with the hemodialysis patients. Twelve of 29 (41.4%) hemodialysis patients with HBsAg infection produced anti-HBs, while 17 (58.6%) remained positive for HBsAg. This differential response could not be attributed to age, sex, time spent undergoing hemodialysis, delayed cutaneous reactivity or response to phytohemagglutinin (PHA) or pokeweed mitogen (PWM). However, a much larger proportion of patients with HBsAg than with anti-HBs had previously received blood transfusions (88.2% v. 33.3%). Our results indicate that development of the chronic HBsAg carrier state or production of anti-HBs in uremic patients may be influenced by the route of immunization or the dose of antigen, or both. Although uremic patients maintain normal in vitro response to PHA and PWM, they may have depressed immunity in vivo because of a decreased total number of T-lymphocytes.

Hepatitis B antigen (HBAg) infection in a hemodialysis unit. I. HL-A8 and immune response to HBAg.

A total of 28 hemodialysis patients and 23 healthy individuals working in close association with the patients or their blood samples were found to possess either HBAg (22) or anti-HBAg (29). HL-A typing revealed the lack of HL-AB in the group with anti-HBAg, suggesting that the immune response to HBAg may be negatively associated with HL-AB.

Beneficial effect of hemodialysis on renal allograft survival.

The effect of the length of hemodialysis on the outcome of renal transplant was evaluated in 43 recipients of renal allograft. 22 out of 23 patients (95.7%) dialyzed for longer than one year had an excellent renal function at one year, while only 10 out of 20 patients (50%) dialyzed for less than one year had good renal function at one year. Only one kidney (4.3%) was lost due to rejection in the first group, while 10 kidneys (50%) failed to function because of severe rejection in the second group. The length of hemodialysis appears to have a beneficial effect on graft survival, but the mechanism by which it exerts this effect is not clear.