Intercrystal scatter studies for a 1 mm3 resolution clinical PET system prototype.

Positron emission tomography (PET) systems designed with multiplexed readout do not usually have the capability to resolve individual intercrystal scatter (ICS) interactions, leading to interaction mispositioning that degrades spatial resolution and contrast. A 3D position sensitive scintillation detector capable of individual ICS readout has been designed and incorporated into a 1 mm3 resolution clinical PET system used for locoregional imaging. Incorporating ICS events increases photon sensitivity by 51.5% compared to using only photoelectric events. A Compton scatter angle error minimization algorithm is used to estimate the first ICS interaction location for accurate line-of-response pairing of coincident photons. An optimal scatter angle error threshold of 15 degrees is used to discard ICS events with a high mismatch between energy-derived and position-derived intercrystal scatter angles. Finally, positioning rather than rejecting ICS events boosts peak contrast to noise ratio by 8.1%, and allows for an equivalent dose reduction of 12% while maintaining equivalent image quality.

Thermal regulation of tightly packed solid-state photodetectors in a 1 mm(3) resolution clinical PET system.

PURPOSE: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased thermal density and constrained options for thermally regulating the devices. This paper proposes a method of thermally regulating densely packed silicon photodetectors in the context of a 1 mm(3) resolution, high-sensitivity PET camera dedicated to breast imaging. METHODS: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm(3) LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed thermal regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. This thermal regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. RESULTS: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. CONCLUSIONS: The proposed thermal regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The thermal regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.

Pediatric "PSC-IBD": a descriptive report of associated inflammatory bowel disease among pediatric patients with psc.

BACKGROUND: Inflammatory bowel disease (IBD) in adults with primary sclerosing cholangitis (PSC) is characterized by pancolonic involvement, a high frequency of rectal sparing, and an increased risk of pouchitis and colorectal neoplasia. The clinical features of IBD in pediatric patients with PSC have not been well described. The aim of this study was to characterize the frequency, clinical features, and natural history of IBD in pediatric patients diagnosed with PSC. METHODS: A retrospective chart review was performed for all patients 18 years of age or younger diagnosed with PSC seen at the Mayo Clinic between 1975 and 1999. Endoscopic and histologic features and surgical and postsurgical outcomes were recorded. RESULTS: Fifty-two children with PSC were identified. Forty-three patients (84%) were also diagnosed with IBD. In 36 of 43 cases, there was a sufficient diagnostic evaluation to allow a detailed review. Thirty-two of 36 patients (89%) had ulcerative colitis and 4 of 36 patients (11%) had Crohn's disease. In 4 of 36 patients (11%), IBD was asymptomatic. Although the most frequent endoscopic presentation of IBD was universal colitis, endoscopic rectal sparing was frequently noted (27% of colonoscopic studies). Of the four patients diagnosed with Crohn disease, in none did perianal, fistulizing, or stricturing disease develop. Proctocolectomy was performed in six patients (17%); three operations were performed for dysplasia. Pouchitis complicated four of the five ileal pouch-anal anastomoses procedures. CONCLUSIONS: Among pediatric patients (1) PSC without IBD is uncommon; (2) asymptomatic IBD may be associated with PSC; (3) because the time to dysplasia may be accelerated, once the diagnosis of IBD is made in the setting of PSC, heightened endoscopic surveillance may be indicated; (4) pouchitis occurs frequently in these patients.

No evidence of hepatitis G virus in fulminant hepatic failure in children.

BACKGROUND: The cause of fulminant hepatic failure in children remains unknown, but a viral origin has been suspected in most cases. The recently discovered blood-borne virus, hepatitis G, has been suggested as a possible causative agent. METHOD: Six consecutive children who underwent liver transplantation for fulminant hepatic failure were studied. The children were tested for hepatitis G virus antibodies and hepatitis G virus RNA by polymerase chain reaction after excluding other causes of fulminant hepatic failure. RESULTS: No evidence of hepatitis G virus infection was found in these patients. CONCLUSION: Hepatitis G virus is unlikely to be a common cause of fulminant hepatic failure in pediatric patients from the upper midwestern United States.

Towards improved information retrieval from medical sources.

We review a HEALNet health informatics project directed at information extraction from medical text resources in support of evidence based practice (EBP). The motivation for the approach is summarized. A brief review of pertinent methodology is given and the rationale for exploring approaches to statistical concept representation (SCR) derived. Data on the qualitative comparison of five related systems are presented. Installation and tests of three of these systems revealed that systems designed to deal with literature are not able to handle medical record text adequately because of various idiosyncrasies of the latter. To overcome these, it is necessary to control the system's text manipulation algorithms. This prompted us to build our own system. The principles of this development and its results are summarized. They include the construction of a core information retrieval (IR) system, which is now operational, initiation of work on the collection of test data bases and development of a conceptual framework for comprehensive system evaluation. A brief outline of further steps concludes the presentation.

Tacrolimus (FK506): the pros and cons of its use as an immunosuppressant in pediatric liver transplantation.

Tacrolimus (FK506) is a new immunosuppressive agent that has recently been given to recipients of liver transplants. Multicentre studies conducted in the United States and Europe have reported that tacrolimus is superior to cyclosporine in preventing allograft rejection. The absorption of tacrolimus is independent of bile, and, therefore, therapeutic blood levels are usually achieved by taking oral preparations within 72 hours of liver transplantation. Compared with the use of cyclosporine, this regimen has resulted in shorter hospital stays and reduced costs. Tacrolimus does not cause hirsutism or gingival hyperplasia, which are common disfiguring complications of cyclosporine. Serious neurological side effects, lymphoproliferative disorders and hypertrophic cardiomyopathy have recently been reported in children taking high doses of tacrolimus. When lower doses of tacrolimus are used in primary immunosuppressive therapy, the incidence of neurological side effects and lymphoproliferative disorders of tacrolimus and cyclosporine have been reported to be similar. Hence, tacrolimus is a potent immunosuppressant that has many advantages over cyclosporine but must be used cautiously, since high doses have been associated with an increased incidence of lymphoproliferative disorders and cardiomyopathy.

Antibody response of pediatric solid organ transplant recipients to immunization against influenza virus.

We studied the immunogenicity of the 1992-1993 trivalent split-virus influenza vaccine in pediatric solid organ transplant recipients (PSOTRs) and their healthy siblings. One month after immunization, 41 (82%) of 50 subjects achieved protective titers of antibodies to influenza A, and 30 (60%) to influenza B, rates similar to those in healthy siblings. Achievement and persistence of protective titers occurred significantly more often in children with preexisting antibody. We recommend annual immunization of PSOTRs, their household contacts, and health care workers; immunologically naive PSOTRs may benefit from immunization before transplantation.

Histologic pathology of the liver in progressive familial intrahepatic cholestasis.

This work details the histologic findings in 84 liver biopsy specimens from 28 patients with progressive familial intrahepatic cholestasis (PFIC), who met the clinical criteria of early onset of chronic unremitting cholestasis, exclusion of any known metabolic or anatomic etiology, and low serum gamma-glutamyl transpeptidase (GGTP) values. Hepato-canalicular cholestasis and disruption of the liver cell plate arrangement were early, uniform findings, and giant cell transformation was found in 56% of initial biopsies. Duct loss was a prominent finding; 70% of patients had ductal paucity, and many had abnormal bile duct epithelium, suggesting degeneration. Fibrosis was seen in the samples from 16 patients, including bridging fibrosis in specimens obtained from six patients during the first 2 years of life. Proliferating ductules at the margins of portal tracts increased as fibrosis progressed and were especially prominent in end-stage histology. Cirrhosis developed in nine of these patients and had a characteristic histologic pattern, consisting of biliary cirrhosis with diffuse stellate lobular fibrosis associated with severe cholestasis and pseudoacinar transformation. Mallory hyalin and hepatocellular carcinoma were observed in materials from some patients with advanced cirrhosis. The constellation of histologic findings in PFIC forms a recognizable pattern, and the liver histology appears to have a predictable progression.

Clinical and biochemical findings in progressive familial intrahepatic cholestasis.

The clinical findings in 33 patients with progressive familial intrahepatic cholestasis (PFIC) are presented. Symptoms developed almost invariably before 6 months of age with severe pruritus and moderate jaundice. Other clinical findings included wheezing and nosebleeds, fat-soluble vitamin deficiency states, and cholelithiasis. Lower values for gamma-glutamyl transpeptidase, averaging 15 IU/L before the administration of phenobarbital, and cholesterol, which averaged 156 mg/dl, are helpful in distinguishing PFIC from other pediatric cholestatic liver diseases. Autosomal recessive inheritance is probable. Twenty-six patients are alive at 12.9 +/- 6.7 years of age, all having had successful surgical treatment, either partial biliary diversion (n = 17) or orthotopic liver transplantation (n = 10). Seven patients died at a mean age of 3.9 +/- 2.4 years, as a result of liver failure in two, hepatocellular carcinoma in two, and complications of liver transplantation in three.

Resolution of severe intrapulmonary shunting after liver transplantation.

A major complication of hepatic cirrhosis is arterial hypoxemia, often the result of intrapulmonary arteriovenous shunting. While previously such hypoxemia was thought to preclude successful hepatic transplantation, more recent studies have suggested that hepatic transplantation should be considered if the hypoxemia is corrected by supplemental oxygen. We report the findings in a cirrhotic patient with severe hypoxemia associated with intrapulmonary arteriovenous shunting. The patient did not respond to supplemental oxygen (PaO2 < 40 mm Hg on O2 at 4 L/min). The patient underwent successful hepatic transplantation, with complete resolution of intrapulmonary shunting. We believe that patients with cirrhosis-associated intrapulmonary shunting, even with hypoxemia resistant to supplemental oxygen, are acceptable candidates for hepatic transplantation.

Success of kidney transplantation in oxalosis is unrelated to residual hepatic enzyme activity.

We evaluated hepatic alanine glyoxylate aminotransferase (AGT) activity in percutaneous hepatic biopsy material obtained from four children with long-term renal allograft function following transplantation for primary hyperoxaluria type 1 (PH 1). The study was performed to determine whether these successes had occurred because relatively high residual levels of AGT activity had introduced a selection bias. The children ranged from seven months to eight years at transplant and are currently well 7 to 11 years later, with no oxalate deposition on repeated allograft biopsies and creatinine clearances of 80 to 128 ml/min/1.73 m2. AGT activity ranged from 0 to 13.8%, and in two of three patients with detectable levels the AGT was in mitochondria rather than peroxisomes. These results indicate that long-term renal allograft success can occur in spite of severe AGT deficiency. Thus, the therapeutic choice of kidney alone versus combined kidney-liver transplant cannot currently be made by measuring residual hepatic AGT in PH 1. Kidney transplant alone remains a reasonable initial therapeutic alternative for patients with recent onset of renal insufficiency due to PH 1.

Long-term complications of arteriohepatic dysplasia.

PURPOSE: It has been stated that arteriohepatic dysplasia is a form of biliary paucity with a good prognosis. We wished to determine the long-term morbidity and mortality associated with arteriohepatic dysplasia. PATIENTS AND METHODS: The charts of all patients with arteriohepatic dysplasia followed by the pediatric gastroenterologists of the University of Minnesota into adulthood were reviewed. RESULTS: Over the last 33 years, the pediatric gastroenterologists have followed 16 children with syndromic paucity, six of whom are now beyond age 18 years. Although five of six patients responded to medical therapy with improvement in their cholestasis and appeared stable clinically through childhood, five of six patients had complications of arteriohepatic dysplasia after age 16 years that resulted in severe morbidity (three) or death (two). These complications included hepatic failure (two), renal failure (one), cerebellar herniation (one), and hepatocellular carcinoma (one). In only one patient were symptoms of the complications present prior to the age of 18 years. CONCLUSION: As more patients with arteriohepatic dysplasia reach adulthood, it appears that this syndrome may be accompanied by long-term manifestations extending beyond childhood. It is important that physicians assuming management of these patients from pediatricians be aware that new abnormalities may appear without warning and that the hepatic disease may deteriorate despite apparent stability through childhood.

Hemolytic anemia in protoporphyria: possible precipitating role of liver failure and photic stress.

Hemolytic anemia is not a common clinical feature in protoporphyria. In this report, we describe two patients in whom we have encountered severe hemolytic anemia. Both individuals had advanced hepatic disease as a complication of their porphyria and were undergoing orthoptic liver transplantation. The onset of hemolysis appeared to be related to the development of liver disease, and in both cases, the operative procedure acutely exacerbated the red cell destructive process. We suggest that liver involvement in protoporphyria may unmask hemolytic anemia, and that red cells in these individuals are hypersensitive to photooxidative stress, such as might occur during a prolonged operative procedure.

Wolman's disease: a review of treatment with bone marrow transplantation and considerations for the future.

Wolman's disease is a fatal disorder characterized by absence of acid lipase and accumulation of cholesterol esters. Inanition due to malabsorption and intractable diarrhea has been the most prominent cause of early demise within the first year. Further complications have included cirrhosis and pulmonary failure due to cholesterol ester storage in respective cells. Although sustained caloric balance can be maintained by total parenteral nutrition, this has not altered the eventual course of disease. The acid lipase deficiency in leucocytes in Wolman's disease can be corrected subsequent to bone marrow transplantation. This has proven to be the case in two patients so transplanted. In two other patients, engraftment was not obtained following bone marrow transplantation. The concept of treatment of Wolman's disease by providing normalization of the acid lipase activity by allogeneic bone marrow transplantation remains valid. However, improvement of bone marrow transplant procedure needs to be implemented since pre-existing morbid pathology enhances toxicity and may prevent engraftment. Alternative modifications for accomplishing sustained engraftment without toxicity need to be examined. Other potential therapies need to be inspected in treatment of patients with Wolman's disease. The capability of reducing cellular cholesterol synthesis by use of lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, is now available. In the future, isolation and purification of acid lipase will allow for direct infusion of missing enzyme. The molecular biology now known concerning acid lipase gene holds promise for the future for recombinant manufacturing of acid lipase. And, gene therapy with its use of autologous bone marrow transplantation will be tried in future.(ABSTRACT TRUNCATED AT 250 WORDS)

The pathologic spectrum of the nephropathy associated with alpha 1-antitrypsin deficiency.

To further define the clinicopathologic spectrum and pathogenetic mechanism of the nephropathy associated with alpha 1-antitrypsin (A1AT) deficiency, we evaluated renal specimens from 34 patients with chronic hepatic disease, including 20 with A1AT deficiency (study patients), and correlated these findings with urinalysis evaluation. Glomerular lesions were noted in 79% (15 of 19) of A1AT patients with the PiZZ phenotype, including seven with mesangio-capillary glomerulonephritis (MPGN and focal segmental MPGN), six with mesangial proliferative glomerulonephritis (Mes GN), one with diffuse endocapillary proliferative glomerulonephritis (DPGN), and one with focal segmental mesangial proliferative glomerulonephritis with segmental necrosis (FS Nec GN). One A1AT patient with the PiMZ phenotype did not demonstrate glomerular abnormalities. Focal segmental Mes GN was found in 43% (six of 14) of patients in an age-matched group with chronic hepatic failure unrelated to A1AT deficiency. In nine study patients, glomerular pathology was noted in the presence of a normal urinalysis. Immunofluorescence studies revealed the presence of immunoproteins and the A1AT protein isoelectric forms, PiM and PiZ, in the subendothelial region of glomerular basement membranes in A1AT patients with MPGN, Mes GN, and DPGN. Our results emphasize the heterogeneity of glomerular lesions associated with A1AT deficiency and hepatic disease and the relatively high incidence of MPGN in these children. The presence of abnormal PiZ protein in the subendothelial region of the glomerular basement membrane in A1AT patients with glomerulonephritis suggests a possible role for this protein in the pathogenesis of this lesion.

Early liver transplantation is indicated for tyrosinemia type I.

Liver transplantation is now accepted as the treatment of choice for tyrosinemia type I (hereditary tyrosinemia). In an effort to determine whether any factors in these patients would aid in predicting optimal timing of the transplant procedure, we evaluated several clinical, biochemical, and radiographic parameters in five successive patients undergoing liver transplant for tyrosinemia type I at the University of Minnesota. All five patients evidenced prolonged periods of clinical and metabolic stability with dietary therapy and four of five remained stable at the time of evaluation for transplantation. Nevertheless, all five suffered significant and unexpected complications of tyrosinemia prior to the time of liver transplant. Four developed renal stones, two were in liver failure, and one developed a neurologic crisis that left him completely paralyzed. Hepatocellular carcinoma was found in one of the five at transplant. We could identify no clinical, biochemical, or radiographic study that was predictive of the likelihood of significant complications of the disorder. Survival from the transplant procedure itself was 100%. The inability to predict or prevent significant complications of tyrosinemia and the favorable outcome from transplantation lead us to recommend liver transplant for all patients with tyrosinemia type I by 12 months of age.