Optimizing the efficiency of high-field multivoxel spectroscopic imaging by multiplexing in space and time.

A new strategy to yield information from the maximum number of voxels, each at the optimum signal-to-noise ratio (SNR) per unit time, in MR spectroscopic imaging (MRSI) is introduced. In the past, maximum acquisition duty-cycle was obtained by multiplexing in time several single slices each repetition time (TR), while optimal SNR was achieved by encoding the entire volume of interest (VOI) each TR. We show that optimal SNR and acquisition efficiency can both be achieved simultaneously by multiplexing in space and time several slabs of several slices, each. Since coverage of common VOIs in 3D proton MRSI in the human brain typically requires eight or more slices, at 3 T or higher magnetic fields, two or more slabs can fit into the optimum TR (approximately 1.6 s). Since typically four or less slices would then fit into each slab, Hadamard encoding is favored in that direction for slice profile reasons. It is demonstrated that per fixed examination length, the new method gives, at 3 T, twice as many voxels, each of the same SNR and size, compared with current 3D chemical shift imaging techniques. It is shown that this gain will increase for more extensive spatial coverage or higher fields.     

Multiple sclerosis: genetic versus environmental aetiology: epidemiology in Israel updated

The incidence and prevalence of multiple sclerosis (MS) were compared, controlling for age, in native-born Israelis of different origins and in immigrants to Israel. This comparison was carried out in two populations, countrywide and in Jerusalem. In the countrywide population, ascertainment was based mainly on hospitalizations; it included 252 patients who were native-born and 150 who had immigrated from Africa-Asia (AA immigrants). The 89 MS patients of Jerusalem also included patients diagnosed in outpatient clinics. In native-born Israelis whose father was born in Europe-America (I-EA), the incidence and prevalence of MS were found to be as high as or even higher than that found previously in immigrants from Europe-America. Among native-born Israelis whose father was born in Africa or Asia (I-AA), the yearly age-adjusted incidence and prevalence rates were found to be 1.4- to 1.8-fold higher than among AA immigrants, pointing to environmental factors. The incidence and prevalence rates in the I-EA were 1.2- to 1.6-fold higher than in the I-AA, pointing to genetic factors. These results seem to point to both environmental and genetic factors in the aetiology of MS. Further research is needed, however, to disentangle the genetic factors from possible environmental differences in the two ethnic groups.     

In vivo phosphorus polarization transfer and decoupling from protons in three-dimensional localized nuclear magnetic resonance spectroscopy of human brain

Refocused insensitive nucleus enhancement by polarization transfer (RINEPT) from protons (¹H) to a J-coupled phosphorus (³¹P) has been incorporated into three-dimensional (3D) chemical-shift-imaging (CSI) sequence on a clinical imager. The technique is demonstrated on a phantom and in in vivo human brain. The polarization-transfer efficiency (～1.2) is lower than the theoretical maximum of γ¹H/γ³¹P≈ 2.4 resulting from ¹H-¹H homonuclear J couplings of similar magnitude competing with the ¹H →³¹P transfer. Nevertheless, compared with direct ³¹P Ernst-angle excitation, signal gains of up to × 1.8 were obtained mainly as a result of T¹ differences between ³¹P and the ¹H. Spectral interpretation is simplified by editing out all non-proton-coupled ³¹P signals. The duration, ～50 min, and power deposition, ～1 W · kg^?1, make the application suitable for human studies.     

A not-so-basic case of metabolic alkalosis: an analysis featuring Leendert Paul and emphasizing Occam’s razor

A patient had the onset of a severe degree of metabolic alkalosis associated with a very large daily loss of diarrheal fluid. Because the expected acid-base disorder in this setting is metabolic acidosis, factors that could result in the markedly increased concentration of bicarbonate (HCO₃⁻) in plasma (P ₃) were sought. In our approach, there is an emphasis on electroneutrality, mass balance, a quantitative analysis, and the application of basic concepts in physiology at the bedside. We suggest that there were 3 major factors that could explain why the P ₃ was so high. First, a severe degree of extracellular fluid volume contraction was probably the most important factor that raised her P ₃. Second, there may have been an unusual way to have an electroneutral addition of HCO₃⁻ and removal of chloride ions from her extracellular fluid compartment. Third, the diarrheal fluid could have contained little HCO₃⁻ because of a down-regulated intestinal secretion of HCO₃⁻. This analysis challenges the traditional pathophysiology of metabolic alkalosis.     

A novel point mutation (I137T) in the conserved 5-phosphoribosyl-1-pyrophosphate binding motif of hypoxanthine-guanine phosphoribosyltransferase (HPRTJerusalem) in a variant of Lesch-Nyhan syndrome

We identified a novel point mutation (I137T) in the hypoxanthine-guanine phosphoribosyltransferase (HPRT; EC 2.4.2.8) encoding gene, in a patient with partial deficiency of the enzyme (variant of Lesch-Nyhan syndrome). The mutation, ATT to ACT, resulting in substitution of isoleucine to threonine, occurred at codon 137 (exon 6), which is within the region encoding the binding site for 5-phosphoribosyl-1-pyrophosphate (PRPP). We suggest the mechanism by which the mutation-induced structural alteration of HPRT reduced the affinity of the enzyme for PRPP.     

Activated status of tumour-infiltrating lymphocytes and apoptosis in testicular seminoma.

Testicular seminoma is characterized by a prominent lymphoid infiltrate and an excellent prognosis. Cytotoxic T-lymphocytes (CTLs) infiltrating seminoma tumour nests constitute a major subset of the lymphoid infiltrate. The objective of this study was to determine whether CTLs express markers of cytotoxic potential and activity and whether the number of activated CTLs correlates with the extent of apoptosis in testicular seminomas, as opposed to non-seminomatous testicular germ cell tumours (NSTGCTs). Twenty cases of pure seminoma as well as 20 cases of NSTGCTs including 16 mixed germ cell tumours (MGCTs) were studied. Immunohistochemistry for the cytotoxic markers TIA-1 (cytotoxic potential) and granzyme B (cytotoxic activity) and the T-cell markers CD3 and CD8 was performed on formalin-fixed, paraffin-embedded sections. The apoptotic index (AI) was determined by the TUNEL method. The number of CD3(+), CD8(+), TIA-1(+), and granzyme B(+) cells in tumour cell nests was markedly increased in testicular seminomas, compared with NSTGCTs (p<0.01). Activated granzyme B(+) cells numbered 25.6+/-5.2 per high power field in seminomas and 8.9+/-3.2, 8.1+/-3.9, and 0.4+/-0.2 for embryonal carcinomas, yolk sac tumours, and immature teratomas, respectively. Double immunohistochemical staining for granzyme B and CD8 revealed that 82.6+/-8.5% of granzyme B-expressing cells were CD8(+). The tumour cell AI was significantly increased in embryonal carcinoma, compared with the seminoma, yolk sac tumour, and immature teratoma subgroups (6.7+/-1.3, 2.3+/-0.3, 3.0+/-1.1, and 2.3+/-1.1, respectively, p<0.001). TUNEL/CD3 double immunostaining revealed that a significant proportion of the apoptotic seminomatous tumour cells were in direct contact with one or more CD3(+) lymphocytes (47.2+/-6.2%). The number of activated granzyme B(+) CTLs showed a strong linear correlation with the AI in the seminoma group (r=0.71, p<0.0001) but not in other subgroups. TUNEL/granzyme B double immunolabelling revealed that a proportion of activated granzyme B(+) lymphocytes (20%) were often seen in close contact with apoptotic tumour cells. The presence of increased numbers of activated cytotoxic lymphocytes in testicular seminomas suggests that apoptotic tumour cell death in this neoplasm may be triggered by cytotoxic granule effectors. This phenomenon may be one of the key host immune mechanisms leading to the excellent prognosis in this tumour.     

Orally administered myelin basic protein in neonates primes for immune responses and enhances experimental autoimmune encephalomyelitis in adult animals

Antigen-driven tolerance is an effective method for suppression of autoimmune diseases. Adult animals can be tolerized against the induction of experimental autoimmune encephalomyelitis (EAE) by both oral and parenteral administration of myelin basic protein (MBP). We have found that in contrast to previous studies of neonatal tolerance in which parenterally administered autoantigens induced tolerance, the oral administration of MBP in neonatal rats did not result in tolerization to MBP, but instead, primed for immunologic responses. Proliferative responses to MBP and its encephalitogenic epitope were present in animals fed with MBP as neonates and co-culture of encephalitogenic T cells with cells from neonatal rats fed with MBP were associated with enhanced MBP responses rather than the suppression observed with cells from adult rats fed with MBP. Furthermore, neonates fed with MBP and immunized 6–8 weeks later with MBP in adjuvant to induce EAE revealed enhancement of disease severity, and were not protected from a second attack upon active reinduction of EAE. Subcutaneous injection of soluble MBP into neonates had no effect on EAE induction as adults, whereas intraperitoneal injection of MBP in neonates was associated with marked suppression of disease in adults. Suppression of EAE began to appear in animals fed with MBP at 4 weeks of age, and was similar to oral tolerance in adult animals when animals were fed at 6 weeks of age. These results suggest that immaturity of the immunoregulatory network associated with oral tolerance and sensitization to autoantigens via the gut in the neonatal period may contribute to the pathogenesis of autoimmune diseases.     

Mast cell activity in experimental allergic encephalomyelitis

The number and functional reactivity of peritoneal mast cells (MCs) were evaluated in rats with experimental allergic encephalomyelitis (EAE). Cells were counted following staining with toluidine blue and activation was measured by B-hexosaminidase (B-hex) release. The number of detectable MCs and their capacity to release B-hex decreased significantly by 40 and 65%, respectively, as compared with normal controls just prior to the onset of clinical signs. These values returned to normal on clinical recovery. Preliminary data on MC counts performed on histological sections of rat brains with EAE suggested a similar pattern of response, i.e., an early decrease prior to disease onset with subsequent normalization on recovery. In an attempt to modify the course of EAE, rats were treated with the MC stabilizing agent nedocromil or with the MC activating agent, compound 48/80. Nedocromil induced a slight delay in the onset of EAE, but only when administered at the time of EAE induction. Compound 48/80 did not seem to affect the clinical course of the disease. Our results suggest that MCs are involved in the pathogenesis of EAE and may contribute to the induction of the disease rather than to the effector phase and its clinical expression.