Improved EMCCD gamma camera performance by SiPM pre-localization.

High spatial resolution γ-imaging can be achieved with scintillator readout by low-noise, fast, electron-multiplying charge-coupled devices (EMCCDs). Previously we have shown that false-positive events due to EMCCD noise can be rejected by using the sum signal from silicon photomultipliers (SiPMs) mounted on the sides of the scintillator. Here we launch a next generation hybrid CCD-SiPM camera that utilizes the individual SiPM signals and maximum likelihood estimation (MLE) pre-localization of events to discriminate between true and false events in CCD frames. In addition, SiPM signals are utilized for improved energy discrimination. The performance of this hybrid detector was tested for a continuous CsI:Tl crystal at 140 keV. With a pre-localization accuracy of 1.06 mm (full-width-at-half-maximum) attained with MLE the signal-to-background ratio (SBR) was improved by a factor of 5.9, 4.0 or 2.2 compared to the EMCCD-only readout, at the cost of rejecting, respectively, 47%, 9% or 4% of the events. Combining the pre-localization and SiPM energy estimation improved the energy resolution from 50% to (19 ± 3)% while maintaining the spatial resolution at 180 µm.

An enhanced high-resolution EMCCD-based gamma camera using SiPM side detection.

Electron-multiplying charge-coupled devices (EMCCDs) coupled to scintillation crystals can be used for high-resolution imaging of gamma rays in scintillation counting mode. However, the detection of false events as a result of EMCCD noise deteriorates the spatial and energy resolution of these gamma cameras and creates a detrimental background in the reconstructed image. In order to improve the performance of an EMCCD-based gamma camera with a monolithic scintillation crystal, arrays of silicon photon-multipliers (SiPMs) can be mounted on the sides of the crystal to detect escaping scintillation photons, which are otherwise neglected. This will provide a priori knowledge about the correct number and energies of gamma interactions that are to be detected in each CCD frame. This information can be used as an additional detection criterion, e.g. for the rejection of otherwise falsely detected events. The method was tested using a gamma camera based on a back-illuminated EMCCD, coupled to a 3 mm thick continuous CsI:Tl crystal. Twelve SiPMs have been mounted on the sides of the CsI:Tl crystal. When the information of the SiPMs is used to select scintillation events in the EMCCD image, the background level for (99m)Tc is reduced by a factor of 2. Furthermore, the SiPMs enable detection of (125)I scintillations. A hybrid SiPM-/EMCCD-based gamma camera thus offers great potential for applications such as in vivo imaging of gamma emitters.

2D dosimetry in a proton beam with a scintillating GEM detector.

A two-dimensional position-sensitive dosimetry system based on a scintillating gas detector is being developed for pre-treatment verification of dose distributions in particle therapy. The dosimetry system consists of a chamber filled with an Ar/CF(4) scintillating gas mixture, inside which two gas electron multiplier (GEM) structures are mounted (Seravalli et al 2008b Med. Phys. Biol. 53 4651-65). Photons emitted by the excited Ar/CF(4) gas molecules during the gas multiplication in the GEM holes are detected by a mirror-lens-CCD camera system. The intensity distribution of the measured light spot is proportional to the 2D dose distribution. In this work, we report on the characterization of the scintillating GEM detector in terms of those properties that are of particular importance in relative dose measurements, e.g. response reproducibility, dose dependence, dose rate dependence, spatial and time response, field size dependence, response uniformity. The experiments were performed in a 150 MeV proton beam. We found that the detector response is very stable for measurements performed in succession (sigma = 0.6%) and its response reproducibility over 2 days is about 5%. The detector response was found to be linear with the dose in the range 0.05-19 Gy. No dose rate effects were observed between 1 and 16 Gy min(-1) at the shallow depth of a water phantom and 2 and 38 Gy min(-1) at the Bragg peak depth. No field size effects were observed in the range 120-3850 mm(2). A signal rise and fall time of 2 micros was recorded and a spatial response of

Characterization of a scintillating GEM detector with low energy x-rays.

A two-dimensional position-sensitive dosimetry system based on a scintillating gas detector is being developed with the aim of using it for pre-treatment verification of dose distributions in charged particle therapy. The dosimetry system consists of a chamber filled with an Ar/CF(4) scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. In such a system, light quanta are emitted by the scintillating gas mixture during the electron avalanches in the GEM holes when radiation traverses the detector. The light intensity distribution is proportional to the energy deposited in the detector's sensitive volume by the beam. In the present work, we investigated the optimization of the scintillating GEM detector light yield. The light quanta are detected by means of a CCD camera or a photomultiplier tube coupled to a monochromator. The GEM charge signal is measured simultaneously. We have found that with 60 microm diameter double conical GEM holes, a brighter light signal and a higher electric signal are obtained than with 80 microm diameter holes. With an Ar + 8% CF(4) volume concentration, the highest voltage across the GEMs and the largest light and electric signals were reached. Moreover, we have found that the emission spectrum of Ar/CF(4) is independent of (1) the voltages applied across the GEMs, (2) the x-ray beam intensity and (3) the GEM hole diameter. On the other hand, the ratio of Ar to CF(4) peaks in the spectrum changes when the concentration of the latter gas is varied.

A scintillating gas detector for 2D dose measurements in clinical carbon beams.

A two-dimensional position sensitive dosimetry system based on a scintillating gas detector has been developed for pre-treatment verification of dose distributions in hadron therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. The primary electrons, created in the detector's sensitive volume by the incoming beam, drift in an electric field towards the GEMs and undergo gas multiplication in the GEM holes. During this process, photons are emitted by the excited Ar/CF4 gas molecules and detected by a mirror-lens-CCD camera system. Since the amount of emitted light is proportional to the dose deposited in the sensitive volume of the detector by the incoming beam, the intensity distribution of the measured light spot is proportional to the 2D hadron dose distribution. For a measurement of a 3D dose distribution, the scintillating gas detector is mounted at the beam exit side of a water-bellows phantom, whose thickness can be varied in steps. In this work, the energy dependence of the output signal of the scintillating gas detector has been verified in a 250 MeV/u clinical 12C ion beam by means of a depth-dose curve measurement. The underestimation of the measured signal at the Bragg peak depth is only 9% with respect to an air-filled ionization chamber. This is much smaller than the underestimation found for a scintillating Gd2O2S:Tb ('Lanex') screen under the same measurement conditions (43%). Consequently, the scintillating gas detector is a promising device for verifying dose distributions in high LET beams, for example to check hadron therapy treatment plans which comprise beams with different energies.

Quantification of liver iron concentration with magnetic resonance imaging by combining T1-, T2-weighted spin echo sequences and a gradient echo sequence.

BACKGROUND: The aim of the study was to quantify hepatic iron by MRI for practical use. METHODS: In twenty-three patients with various degrees of iron overload, measurements were carried out with a 1.5 Tesla MR unit. A combination of pulse sequences (T1, T2 and gradient echo) enabled us to quantify smaller amounts of liver iron as accurately as larger amounts of liver iron. The gradient echo sequence provided us with a good correlation when detecting smaller amounts of iron in the liver where the T1 sequence provided a good correlation when larger amounts of iron were present. RESULTS: The combination of the three sequences showed a nice correlation (r=-0. 93, P<0.001) and provided us with an accurate estimate of the liver iron content (LIC). This correlation was achieved with a LIC from the lower range of normal up to LIC of 146 mmol/kg dry weight, which seems the highest measurable liver iron content for a 1.5 Tesla MRI. Measuring in the lower range makes it possible to decide whether further invasive diagnostic investigations by a liver biopsy are indicated. CONCLUSION: MRI is a useful tool to quantify iron overload non-invasively. In cases where a liver biopsy is hazardous MRI can easily be used to obtain reliable, quantitative information about the initial LIC. Quantification by MRI could also be used for follow up of the iron content during depletion treatment by phlebotomy or iron chelation. The stronger the magnet the more sensitive the detection of concentrations up to 150 mmol/kg is. A semi-quantitative judgement will only be possible with severe iron overload over 150 mmol/kg. If such an iron excess is found, a liver biopsy should be performed to exclude cirrhosis.

Molecular cloning, expression and physical mapping of the human methionine synthase reductase gene.

Methionine synthase reductase (EC 2.1.1.135) is a flavoprotein essential for maintenance of methionine synthase in an active state. We characterized the human gene for methionine synthase reductase (MTRR). The gene is approximately 34kb and comprises 15 exons, varying in size from 43 to 1213bp, and 14 introns whose sizes vary from 108bp to 5kb. The positions of several junctions are conserved between the MTRR gene and the C. elegans ortholog, as well as with the rat cytochrome P450 reductase gene. A 1.3kb CpG island encompasses the 5'-flanking region and exon 1 and extends into intron 1. A short region including the transcription start site is sufficient to confer promoter activity, with a better outcome when accompanied by intron 1. The promoter region contains putative binding sites for Sp1, AP-1, AP-2 as well as CAAT motifs, but no consensus TATA box. Primer extension analysis revealed a single major transcription start site, located 137bp upstream of the previously reported initiator ATG. An alternative splicing event involving a portion of exon 1 predicts that translation can potentially be initiated at two different ATG codons. The gene was physically assigned to a narrow area between markers WI1755 and D5S1957.

Major clinical events, signs and severity assessment scores related to actual survival in patients who died from primary biliary cirrhosis. A long-term historical cohort study.

BACKGROUND/AIMS: One of the prognostic methods for survival in primary biliary cirrhosis (PBC) is the Mayo model, with a time-scale limited to 7 years. The aim of our study was to assess how major clinical events, signs, several severity assessment methods and Mayo survival probabilities fit in with actual patient survival, by using yearly observations until 0.5 years before patient death from PBC. METHODOLOGY: Data of 32 patients dying from PBC were collected prior to death at -0.5, -1, -2 etc. years (median: -5 years, range: -16 to -0.5 years). Major events registered were: first occurrence of ascites, upper gastrointestinal bleeding or manifest hepatic encephalopathy and signs, first observation of spider naevi or purpura. Severity assessment methods applied (all with scores and classes) were: Mayo (M), Child-Campbell (C), Pugh-Child (P), Pugh-Child-PBC (PP), 'Child-Pugh' (CP), and Ascites Nutritional State-Child (ANS). Fifty percent survival estimates were calculated from Mayo scores. Severity assessment method variables were: ascites (C, P, PP, CP, ANS), encephalopathy (C, P, PP, CP), nutritional state (C, ANS), edema (M), age (M), serum albumin (M, C, P, PP, CP), bilirubin (C, M, P, PP, CP), and prothrombin time (M, P, PP, CP). RESULTS: In 27 out of 32 patients a major event occurred, always between -6 and -0.5 years (median: -1 year) and, never between -16 and -7 years (p < 0.0001). A sign was first observed in 30/32 between -14 and -0.5 years (median: -2 years). Compared to the total population, a sign, and even more so, an event indicated a shorter survival (p = 0.004 and p = 0.0002, respectively). The median 50% estimated survival (predicted by the Mayo model) fitted the actual survival from -6 to -0.5 years (r = -0.7, p < 0.0001), but not from -16 to -7 years (r = -0.1, p = 0.4). All -6 to -0.5-year severity scores correlated (p < 0.0001) both with actual survival (M, C, P, PP, and CP r = 0.7; ANS r = 0.5) and with estimated M 50% survival (C, P, PP, CP r = -0.9; ANS r = -0.6; M score: -0.99), but none with actual survival from -16 to -7 years, except for M, slightly (r = -0.3, p = 0.04). A nomogram for mean C, CP, M and ANS scores related to actual survival was constructed for the -6 to -0.5-year period. The C and CP classes A, B, and C did not appear to distinguish sufficiently into actual survival, whereas the M classes did. CONCLUSIONS: The occurrence of a major event appeared to exclude survival over 6 years. In these final 6 years, Child-Campbell, Mayo and Pugh scores correlated equally well with actual survival and better than Ascites/Nutritional State score. In our PBC patients, Campbell was an excellent alternative for Pugh; for Pugh, the original Child-Turcotte variable limits were fully sufficient.

Respiratory ammonia output and blood ammonia concentration during incremental exercise.

The aim of this study was to investigate whether the increase of ammonia concentration and lactate concentration in blood was accompanied by an increased expiration of ammonia during graded exercise. Eleven healthy subjects performed an incremental cycle ergometer test. Blood ammonia, blood lactate and the amount of expired ammonia were measured until 30 minutes post exercise. The expired air was guided through a flow chamber filled with a sulphuric acid solution to trap the expired ammonia. Blood ammonia, blood lactate increased more than proportionally and the amount of expired ammonia (in micromol/min) increased exponentially with the workload. Post-exercise the amount of expired ammonia decreased within a few minutes back to pre-exercise levels while the concentrations of lactate and ammonia in blood decreased much more slowly and were still elevated after 30 minutes of recovery. We conclude that the more than proportional increase of ammonia and lactate during graded exercise, is accompanied with an exponential increase of expired ammonia output. Faster and more accurate ammonia gas detection techniques are necessary to quantify more precisely the respiratory ammonia output during graded exercise.

Helicobacter pylori and ammonia concentrations of whole, parotid and submandibular/sublingual saliva.

The aim of this study was to determine the ammonia concentration in whole, parotid and submandibular/sublingual saliva of healthy volunteers using the indophenol direct method. It also investigated the hypothesis that higher saliva ammonia concentrations are associated with the presence of Helicobacter pylori (H. pylori) in the oral cavity. In healthy volunteers, the mean ammonia concentration of whole saliva (2574 mumol/l) was significantly higher (P < 0.0001) than the mean ammonia concentration of both parotid (238 mumol/l) and submandibular/sublingual (355 mumol/l) saliva. In whole saliva, no difference in ammonia concentration was found between healthy controls and dyspeptic patients (mean ammonia values 2574 and 2489 mumol/l respectively, P = 0.7). In addition, no significant differences were observed in the salivary ammonia concentration between dyspeptic patients with and without H. pylori carriage. It is concluded that the ammonia concentration in parotid and submandibular/sublingual saliva does not differ, but is significantly lower than the ammonia concentration of whole saliva. This difference is not due to carriage of H. pylori with its strong urease activity. Therefore, the determination of ammonia in whole saliva is an inappropriate screening test for patients being at risk for (chronic) gastritis and peptic ulcer disease.

Mutations in a gene encoding a novel protein tyrosine phosphatase cause progressive myoclonus epilepsy.

Lafora's disease (LD; OMIM 254780) is an autosomal recessive form of progressive myoclonus epilepsy characterized by seizures and cumulative neurological deterioration. Onset occurs during late childhood and usually results in death within ten years of the first symptoms. With few exceptions, patients follow a homogeneous clinical course despite the existence of genetic heterogeneity. Biopsy of various tissues, including brain, revealed characteristic polyglucosan inclusions called Lafora bodies, which suggested LD might be a generalized storage disease. Using a positional cloning approach, we have identified at chromosome 6q24 a novel gene, EPM2A, that encodes a protein with consensus amino acid sequence indicative of a protein tyrosine phosphatase (PTP). mRNA transcripts representing alternatively spliced forms of EPM2A were found in every tissue examined, including brain. Six distinct DNA sequence variations in EPM2A in nine families, and one homozygous microdeletion in another family, have been found to cosegregate with LD. These mutations are predicted to cause deleterious effects in the putative protein product, named laforin, resulting in LD.

Human PON2 gene at 7q21.3: cloning, multiple mRNA forms, and missense polymorphisms in the coding sequence.

We report the cloning and characterization of human PON2, a paraoxonase-related gene-2 that is physically linked with PON1 and PON3 on 7q2l.3. PON2 is ubiquitously expressed and we identified several mRNA forms produced by alternative splicing, or by the use of a second transcription start site. We also describe two polymorphisms in the coding sequences that, in the protein deduced from the longest open reading frame, predict an alanine-to-glycine substitution at residue 147 and a serine-to-cysteine substitution at residue 310.

Determination of ammonia in cerebrospinal fluid using the indophenol direct method.

We have determined ammonia in cerebrospinal fluid (CSF) with the indophenol direct method. The results were compared with an enzymatic method. The method is very simple, and precision (coefficient of variation 1.6%) and linearity (r = 0.9999, p < 0.001) of the method are excellent. The recoveries of the method are very good (within-sample recovery: range 88-93, median 93%; between-sample recovery: 88-93, median 91%). In a population of 23 neurological patients not suffering from liver disease, the reference values ranged from 8 to 26, median 18 microM. Males and females did not differ (p = 0.5). The values obtained with the indophenol method were equal to the enzymatic method (range 9-28, median 18 microM, p = 0.6). On storage in the deep freeze (-20 degrees C), there was no change in CSF ammonia concentration for at least 1 mo. When stored at 4 degrees C (refrigerator), ammonia determinations have to be performed within 2 d. CSF storage at room temperature results in artificially elevated ammonia levels and should be avoided.

The human metabotropic glutamate receptor 8 (GRM8) gene: a disproportionately large gene located at 7q31.3-q32.1.

Metabotropic glutamate receptors (GRMs), which constitute a family of genes, are neurotransmitter receptors that respond to glutamate stimulations by activating GTP-binding proteins and modulating second-messenger cascades. Pharmacological and expression studies of the rodent Grm8 gene suggest it could be a presynaptic receptor modulating glutamate release at the axon terminals. To study human GRM8, we have determined its nucleotide sequence and genomic organization. While the coding region of the gene spans only 2.3 kb, the gene encompasses approximately 1000 kb of DNA at the boundary of the q31.3-q32.1 bands of chromosome 7. This observation is relevant to the study of Smith-Lemli-Opitz syndrome and an autosomal dominant form of retinitis pigmentosa (RP10), since they map to the same region.

Primary biliary cirrhosis: Dutch application of the Mayo Model before and after orthotopic liver transplantation.

BACKGROUND/AIMS: A retrospective study of primary biliary cirrhosis (PBC) was performed to study the Original Mayo Model for predicting survival by a Dutch data-set of patients, presentation of disease progression; assessment of liver transplantation, prediction of post-transplantation survival; and the addition of two laboratory variables to the Original Mayo Model. MATERIALS AND METHODS: Survival of 83 patients, 37 of whom underwent transplantation, were studied. Mean follow-up was 6.0 +/- 0.45 SEM years. Risk score at diagnosis, platelet count, and serum sodium were analyzed in a Cox model. RESULTS: The Original Mayo Model estimated survival for low-, medium-, and high-risk groups accurately and it also presented disease progression. Baseline Mayo risk score in a Cox model had a regression coefficient of 1.01, indicating an excellent predictor p < 0.0001. Platelet count was a predictor of survival (p < 0.002), whereas serum sodium did not (p = 0.67). A new model combined of the Original Mayo risk score and platelet count predicted survival in high-risk patients somewhat better compared to the Original Mayo Model. With both models, liver transplantation had a significant beneficial effect on survival (p < 0.001). The scores revealed no significant influence (p = 0.47) for overall post-transplantation survival. CONCLUSIONS: The Original Mayo Model remains the model of choice for patients with PBC for prognostication from 3-8 years, is a useful tool in the assessment of liver transplantation but not an indicator of post-transplantation survival. Platelet count showed to have additional prognostic value. A new model combined of platelet count and the Original Mayo risk score did predict survival in high-risk groups slightly better compared to the Original Mayo Model.

Loss of heterozygosity and reduced expression of the CUTL1 gene in uterine leiomyomas.

Cytogenetic analyses has revealed deletions and/or rearrangments at several chromosomal positions in approximately half of uterine leiomyomas. The most frequent genetic alteration, deletion of 7q22, was found in approximately 35% of studied cases with cytogenetic abnormalities (128/366=35%). The same chromosomal band was also found to be deleted in a fraction of acute myeloid leukemias and myelodysplastic syndromes. The frequent deletion of 7q22 in some tumors suggest that a tumor suppressor gene may be located in this region. The human Cut-like homeobox gene, CUTL1, is one of the genes localized to 7q22 and it was shown previously to encode a transcriptional repressor that down-modulates the expression of c-Myc. Activation of the c-Myc oncogenic potential has been shown in many cancers to result from alterations in one or the other of its several mechanisms of regulation. These observations led us to hypothesize that CUTL1 could act as a tumor suppressor gene. In the present study, we have identified polymorphic markers within and directly adjacent to CUTL1 at 7q22 and demonstrated that these markers are present in a commonly deleted region in seven out of 50 uterine leiomyomas samples examined. Furthermore, Northern blot analysis revealed that CUTL1 mRNA levels were reduced in eight tumors out of 13. These results suggest that CUTL1 may act as a tumor suppressor gene whose inactivation could be of pathological importance in the etiology of uterine leiomyomas.

High prevalence of hepatitis G virus after liver transplantation without apparent influence on long-term graft function.

BACKGROUND/AIMS: Hepatitis G virus is a recently characterized transfusion-transmissible RNA virus. Its pathogenicity remains to be established. We studied its prevalence in liver transplant patients and assessed the long-term influence on the liver graft. METHODS: Thirty-nine adult patients without hepatitis B or C were included; median follow-up was 8 years (range 1-17). Serum samples from before and late after transplantation were investigated for the presence of HGV-RNA. HGV-RNA was detected by cDNA-PCR, using primers from the NS3 region of the viral genome. The latest available yearly liver biopsy was assessed in a coded fashion according to established histological criteria. The outcome in the HGV-positive patients was compared with the outcome in the HGV-negative patients with respect to liver tests and liver histology. RESULTS: The prevalence before and after transplantation was 15.4 and 43.6%, respectively. Liver test results and liver histology did not differ between the HGV and non-HGV groups. In both groups more than 50% of the patients showed normal histology. Mild portal and/or lobular inflammation tended to be more prevalent in the non-HGV group (no statistical difference). CONCLUSIONS: HGV infection is highly prevalent in liver transplant patients. In the absence of co-infection with hepatitis B or C virus, no long-term negative influence on the graft occurs.

Whole blood and plasma water in health and disease: longitudinal and transverse observations and correlations with several different hematological and clinicochemical parameters.

In a healthy reference population, hemoglobin (Hgb) and hematocrit (Hct) have been proposed as surrogate markers for whole blood water (WBW). We have extended this study under different physiological and pathological conditions in two longitudinal series, viz. (1) acute hyper- and hypohydration experiments in a healthy individual and (2) three athletes running 5 km each, and in three transverse series, viz. (3) a young reference population (n = 97, 49 females), (4) an old reference population (n = 37, nine females) consisting of inhabitants of a nursing home and (5) cardiac, hematological and renal patients including severe anaemia, polycythaemia and abnormal protein levels (n = 50, 25 females) with suspected hydration disturbances. The only sex difference found was a lower WBW in males in the young reference group. The percentage change of PW was less than that of WBW. In all five groups together (n = 293) WBW correlated closely (P < 0.0001) with Hgb and Hct (both r = -0.95) and with erythrocyte count (r = -0.85), whereas PW correlated with total protein (Tprot) (r = -0.84). In the longitudinally studied groups (1) and (2) WBW also correlated (P < 0.0001) with cholesterol, Ca, Tprot, albumin, platelets, globulin and white blood cells (r +/- 0.98-0.37), while PW correlated (P < 0.0001) not only with the same clinicochemical parameters but also with Hct, Hgb and red blood cells (r +/- 0.98-0.44). The homeostasis of PW is more narrowly regulated than that of WBW. Hgb, Hct and erythrocyte count reflect WBW and Tprot reflects PW also under disease conditions. WBW (mass%) can be calculated from Hgb and Hct using the formulae: -0.09 x Hgb (g/l) + 91.7 and -28.6 x Hct (v/v) + 91.8 and PW (mass%) from Tprot using the formula: -0.09 x Tprot (g/l) + 97.6. Other correlations were observed only in a longitudinal setting and presumably are due to concentration and dilution.

Lactate and ammonia concentration in blood and sweat during incremental cycle ergometer exercise.

It is known that the concentrations of ammonia and lactate in blood increase during incremental exercise. Sweat also contains lactate and ammonia. The aim of the present study was to investigate the physiological response of lactate and ammonia in plasma and sweat during a stepwise incremental cycle ergometer exercise test in ten subjects. During this test lactate and ammonia were measured in blood obtained from the earlobe and in sweat collected in a bag attached to the back of the subject. At the end of each interval this bag was emptied for measuring lactate and ammonia. A disproportional increase in the concentration of lactate and ammonia in blood was found, in sweat a disproportional decrease. The lactate concentrations in sweat were higher than those in blood. We hypothesise that lactate in sweat is produced from glycogen granules of the clear cell of the eccrine gland. This lactate production results in acidification of sweat, which facilitates the diffusion of ammonia from eccrine duct cell to duct lumen. It is uncertain how far duct cell ammonia originates from plasma, the duct cell itself might produce ammonia. Part of the ammonia in sweat could come from the breakdown of urea by skin bacteria.