Real‐time RF pulse adjustment for B0 drift correction

Although the magnetic field of an MR scanner is very stable under little or no load, it can become less stable under heavy‐duty cycle conditions, such as in diffusion tensor imaging (DTI). Uncorrected, such field drifts lead to an apparent image shift along the phase‐encoding direction and decreasing effectiveness of fat saturation pulses. A method is presented to adjust the center frequency of all RF pulses and the receiver in real time during the acquisition. No data postprocessing or changes to the sequence timing are necessary. In vivo acquisitions were performed to assess the prolonged effectiveness of fat saturation. Field drifts of approximately 2.5 Hz/min were measured and corrected during DTI acquisitions at b‐values of up to 3000 s/mm². The effectiveness of fat saturation diminished over the duration of an 18‐min acquisition when the drift was left uncorrected. The proposed method corrects for apparent image shift and ensures continuously effective fat saturation over the duration of an acquisition. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.     

Initial two-year results of the Oregon Liver Transplantation Program

During the first 24 months of the Oregon Liver Transplantation Program, which began in October 1988, 94 patients were formally evaluated and 47 adults underwent 54 liver transplantations. Thirty-four percent of patients were veterans. The recipient operation lasted a mean of 7.4 hours (range: 4 to 16 hours). Veno-venous bypass was used routinely at first but selectively later (7 of the last 26 cases), resulting in reduced operating time. Hepatic artery reconstruction was end-to-end anastomosis in 52 cases and iliac conduit in 2. No arterial thrombosis occurred. Biliary reconstruction was choledochocholedochostomy in 83% and choledochojejunostomy in 17%. Biliary complications occurred in 28%. Operative mortality was 2%, and 1-year actual survival was 80%. Patients with hepatitis B fared worse, with four of six dying at a mean of 7.6 months. Overall, the median hospital stay was 30 days. Patients surviving more than 3 months had a mean Karnofsky score of 82%. No significant difference in outcome was noted in patients receiving prophylactic OKT3 monoclonal antibody (used in 45%) versus conventional immunosuppressive therapy. Overall, allograft rejection occurred in 55% of patients. Retransplantation was required in seven patients, three for primary graft nonfunction, two for uncontrolled rejection during induction therapy with OKT3, and two for graft failure secondary to recurrent hepatitis B.     

Liver transplantation for severe Amanita phalloides mushroom poisoning

Amanita phalloides mushroom poisoning is an increasingly common and potentially lethal problem for which liver transplantation offers definitive therapy in selected patients. When significant liver dysfunction appears, early transfer to a liver transplant center is important to identify appropriate candidates and to begin the search for a donor organ. The clinical course of five severely poisoned patients, four of whom underwent liver transplantation, is reviewed. Indications for transplantation included primarily a markedly prolonged prothrombin time that was only partially correctable and a constellation of findings including metabolic acidosis, hypoglycemia, hypofibrinogenemia, and increased serum ammonia, following a marked elevation in serum aminotransferase levels. Unlike viral fulminant hepatic failure, grade III or IV hepatic encephalopathy, marked elevation of the serum bilirubin level, and azotemia were not indications for transplantation. Resected livers demonstrated hepatocyte viability of 0% to 30%. Manifestations of Amanita poisoning complicating preoperative and/or postoperative care included severe diarrhea, gastrointestinal hemorrhage, hypophosphatemia, bowel edema, and marrow suppression with lymphopenia, thrombocytopenia, and neutropenia. All five patients are well 1 year later. This largest experience with liver transplantation for Amanita poisoning further defines the early clinical and laboratory indications for, and the unique complicating features of, transplantation in this setting.     

Comparison of photocoagulation with the argon, krypton, and diode laser indirect ophthalmoscopes in rabbit eyes.

PURPOSE: The purpose of this study is to compare photocoagulation with the argon green, krypton red, and diode infrared laser indirect ophthalmoscopes in an experimental setting. METHODS: Photocoagulation was performed with each of the laser indirect ophthalmoscopes in a grid pattern within one sector of the same eye of 14 Dutch-belted rabbits. Treatment was performed either with or without scleral depression. Measurements of the retinal burn diameters were performed after hemisecting the globes, and the burns were examined with light microscopy. RESULTS: Variation in burn intensity and diameter (10% to 28%) was common with all 3 laser indirect ophthalmoscopes. Five times more output energy was required to make equivalent burns with the diode laser indirect ophthalmoscope than with the argon or krypton laser indirect ophthalmoscopes. Choriovitreal hemorrhages only occurred during scleral depression. Histopathologically, the argon green laser indirect ophthalmoscope burns spared the choroid and inner sclera, while the intense krypton and diode burns had full-thickness choroidal involvement and even thermal injury to the inner sclera. Scleral depression reduced the mean energy required to create equivalent burns with all three laser indirect ophthalmoscopes. There was a 10% to 40% reduction in the mean retinal burn diameter with scleral depression (argon green, P < 0.0005; krypton red, P < 0.0005; and diode, P < 0.025). CONCLUSION: Photocoagulation with the argon green, krypton red, or diode infrared laser indirect ophthalmoscopes is a safe and effective method of retinal ablation. Decreasing the posterior nodal distance of the eye with scleral depression will produce a smaller spot on the retina with the laser indirect ophthalmoscope.     

Blood transfusion-induced suppression of delayed-type hypersensitivity to allogeneic histocompatibility antigens

In this study delayed-type hypersensitivity against histocompatibility antigens in mice was suppressed by a single donor-specific blood transfusion. Whole blood as well as purified white blood cells and purified red blood cells were capable of inducing suppression. White cells appeared more potent in inducing suppression than red cells. Suppression was dose-dependent, still detectable after administration of as little as 0.001 ml of whole blood and maximal at a dose of 0.1 ml. The suppression was already present a few hours after transfusion and proved to be long-lasting. The suppressive effect could be transferred to naive recipients by Thy-1+, L3T4-, Lyt-2+ spleen cells. This suppressor T cell population was of recipient origin--which excludes the possible involvement of "veto cells" and suppresses the afferent phase as well as the efferent phase of the DTH response.     

Frequencies of background immunoglobulin-secreting cells in mice as a function if organ, age, and immune status

The influence of hereditary absence of thymus and spleen upon the numbers, organ, and class distribution of background immunoglobulin Ig-secreting cells was studied in mice by means of the protein-A plaque assay. In young adult BALB/c mice the spleen contained the largest number of Ig-secreting cells (about 0.5% ). The absolute number of Ig-secreting cells in the spleen was larger than the estimate for all lymph nodes together. Between 8 and 40 weeks of age, the number of Ig-secreting cells in spleen and lymph nodes increased by a factor of 3, maximally. In the same period, the number of Ig-secreting cells in the bone marrow, however, increased by a factor of 20, so that it became the major site of Ig synthesis. Hereditary absence of the spleen did hardly or not at all affect the number of Ig-secreting cells in the other lymphoid organs. However, the athymic state did affect the organ distribution. The most consistent finding was the decreased number of Ig-secreting cells in the Peyer's patches.The class distribution of Ig-secreting cells was found to be independent of the presence of the spleen, but did depend on the presence of the thymus. Athymic mice had a higher percentage of IgM-secreting cells and a lower percentage of IgA-secreting cells. The percentage of IgG₁- and IgG₂-secreting cells did not differ clearly between normal and athymic mice. Percent-wise, most IgM-secreting cells occurred in the spleen, whereas most IgG₁-, IgG₂-, and IgA-secreting cells occurred in the bone marrow, lymph nodes, and Peyer's patches.The specificity repertoire of the background Ig-secreting cells was tested by determining the frequencies of IgM-producing cells with specificity for a panel of six different antigens. These frequencies ranged from 1 in 85 for nitroiodophenyl(NIP)-conjugated sheep erythrocytes (SRBC) till 1 in 1500 for unconjugated SRBC and were found to be the same for the spleen of germ-free and specific pathogen-free (SPF) C3H mice, and for spleen, bone marrow, and thymus of SPF C3H mice.     

The distribution of cytoplasmic immunoglobulin containing cells over various lymphoid organs of congenitally athymic (nude) mice as a function of age.

The distribution of cells containing cytoplasmic immunoglobulin (C-Ig cells) over various lymphoid organs was studied in congenitally athymic (nude) mice as a function of age. The C-IgM, C-IgG and C-IgA cells were enumerated in spleen, bone marrow, mesenteric lymph node and Peyer''s patches of nude mice and their heterozygous littermates of 6, 40 and 100 weeks of age. In the nude as well as in the heterozygous mice an age-related shift was observed in the localization of the C-Ig cells. In young mice of both groups the majority of these cells resided in the spleen, whereas in adult and old mice the bone marrow was found to be the major C-Ig cell organ, indicating that this shift is not dependent on the presence of the thymus. In young and adult nude and heterozygous mice C-Ig cell numbers in the spleen were comparable, whereas C-Ig cell numbers in the other lymphoid organs were higher in the heterozygous mice than in the nude mice. The total C-Ig cell number in young and adult nude mice was lower than in heterozygous mice of the same age, whereas in old nude mice they were as high as in heterozygous mice of the same age, indicating a retarded development of the immunological activity in nude mice. C-Ig cells in nude mice were almost exclusively of the IgM class, although in the bone marrow of the oldest animals also a substantial number of C-IgG and C-IgA cells was observed. Our finding that nude mice can live up to at least two years of age indicates that the age-related deterioration of the thymus-dependent limb of the immune system is not the cause of ageing, but rather a consequence of it.