Improving image quality of sparse-view lung tumor CT images with U-Net

BACKGROUND

We aimed to improve the image quality (IQ) of sparse-view computed tomography (CT) images using a U-Net for lung metastasis detection and determine the best tradeoff between number of views, IQ, and diagnostic confidence.

METHODS

CT images from 41 subjects aged 62.8 ± 10.6 years (mean ± standard deviation, 23 men), 34 with lung metastasis, 7 healthy, were retrospectively selected (2016-2018) and forward projected onto 2,048-view sinograms. Six corresponding sparse-view CT data subsets at varying levels of undersampling were reconstructed from sinograms using filtered backprojection with 16, 32, 64, 128, 256, and 512 views. A dual-frame U-Net was trained and evaluated for each subsampling level on 8,658 images from 22 diseased subjects. A representative image per scan was selected from 19 subjects (12 diseased, 7 healthy) for a single-blinded multireader study. These slices, for all levels of subsampling, with and without U-Net postprocessing, were presented to three readers. IQ and diagnostic confidence were ranked using predefined scales. Subjective nodule segmentation was evaluated using sensitivity and Dice similarity coefficient (DSC); clustered Wilcoxon signed-rank test was used.

RESULTS

The 64-projection sparse-view images resulted in 0.89 sensitivity and 0.81 DSC, while their counterparts, postprocessed with the U-Net, had improved metrics (0.94 sensitivity and 0.85 DSC) (p = 0.400). Fewer views led to insufficient IQ for diagnosis. For increased views, no substantial discrepancies were noted between sparse-view and postprocessed images.

CONCLUSIONS

Projection views can be reduced from 2,048 to 64 while maintaining IQ and the confidence of the radiologists on a satisfactory level.

RELEVANCE STATEMENT

Our reader study demonstrates the benefit of U-Net postprocessing for regular CT screenings of patients with lung metastasis to increase the IQ and diagnostic confidence while reducing the dose.

KEY POINTS

• Sparse-projection-view streak artifacts reduce the quality and usability of sparse-view CT images. • U-Net-based postprocessing removes sparse-view artifacts while maintaining diagnostically accurate IQ. • Postprocessed sparse-view CTs drastically increase radiologists' confidence in diagnosing lung metastasis.

Physical strain while wearing personal radiation protection systems in interventional radiology

Objectives

Multiple studies show orthopedic health problems for medical staff due to wearing radiation protection aprons. The aim of this study was to evaluate the weight pressure on the shoulder as a marker of physical strain caused by different radiation-protection devices.

Methods

For the weight pressure measurement, a pressure sensor (OMD-30-SE-100N, OptoForce, Budapest, Hungary) placed on the left and right shoulder was used. Wearing different radiation protection systems the force measurement system was used to quantify the weight pressure. Measurements were acquired in still standing position and during various movements.

Results

A mean significant decreasing weight pressure on the shoulder between 74% and 84% (p<0.001) was measured, when the free-hanging radiation protection system was used in comparison to one-piece and two-piece radiation protection aprons and coats. Using two-piece radiation protection aprons, the weight pressure was significantly lower than that of one-piece radiation protection coats. If a belt was used for the one-piece radiation protection coat, the weight pressure on the shoulder was reduced by 32.5% (p = 0.003). For a two-piece radiation protection apron and a one-piece radiation protection coat (with and without belt) a significant different weight pressure distribution between the right and left shoulder could be measured.

Conclusions

The free-hanging radiation protection system showed a significant lower weight pressure in comparison to the other radiation protection devices. Apart from this, use of a two-piece radiation protection apron or addition of a belt to a radiation protection coat proved to be further effective options to reduce weight pressure.

Efficient, high-performance semantic segmentation using multi-scale feature extraction

The success of deep learning in recent years has arguably been driven by the availability of large datasets for training powerful predictive algorithms. In medical applications however, the sensitive nature of the data limits the collection and exchange of large-scale datasets. Privacy-preserving and collaborative learning systems can enable the successful application of machine learning in medicine. However, collaborative protocols such as federated learning require the frequent transfer of parameter updates over a network. To enable the deployment of such protocols to a wide range of systems with varying computational performance, efficient deep learning architectures for resource-constrained environments are required. Here we present MoNet, a small, highly optimized neural-network-based segmentation algorithm leveraging efficient multi-scale image features. MoNet is a shallow, U-Net-like architecture based on repeated, dilated convolutions with decreasing dilation rates. We apply and test our architecture on the challenging clinical tasks of pancreatic segmentation in computed tomography (CT) images as well as brain tumor segmentation in magnetic resonance imaging (MRI) data. We assess our model’s segmentation performance and demonstrate that it provides performance on par with compared architectures while providing superior out-of-sample generalization performance, outperforming larger architectures on an independent validation set, while utilizing significantly fewer parameters. We furthermore confirm the suitability of our architecture for federated learning applications by demonstrating a substantial reduction in serialized model storage requirement as a surrogate for network data transfer. Finally, we evaluate MoNet’s inference latency on the central processing unit (CPU) to determine its utility in environments without access to graphics processing units. Our implementation is publicly available as free and open-source software.

Lung nodule detection in chest X-rays using synthetic ground-truth data comparing CNN-based diagnosis to human performance

We present a method to generate synthetic thorax radiographs with realistic nodules from CT scans, and a perfect ground truth knowledge. We evaluated the detection performance of nine radiologists and two convolutional neural networks in a reader study. Nodules were artificially inserted into the lung of a CT volume and synthetic radiographs were obtained by forward-projecting the volume. Hence, our framework allowed for a detailed evaluation of CAD systems' and radiologists' performance due to the availability of accurate ground-truth labels for nodules from synthetic data. Radiographs for network training (U-Net and RetinaNet) were generated from 855 CT scans of a public dataset. For the reader study, 201 radiographs were generated from 21 nodule-free CT scans with altering nodule positions, sizes and nodule counts of inserted nodules. Average true positive detections by nine radiologists were 248.8 nodules, 51.7 false positive predicted nodules and 121.2 false negative predicted nodules. The best performing CAD system achieved 268 true positives, 66 false positives and 102 false negatives. Corresponding weighted alternative free response operating characteristic figure-of-merits (wAFROC FOM) for the radiologists range from 0.54 to 0.87 compared to a value of 0.81 (CI 0.75-0.87) for the best performing CNN. The CNN did not perform significantly better against the combined average of the 9 readers (p = 0.49). Paramediastinal nodules accounted for most false positive and false negative detections by readers, which can be explained by the presence of more tissue in this area.

Treatment of intestinal tuberculosis with small bowel perforation: a case report

Background

Diagnosis of intestinal tuberculosis poses a dilemma to physicians due to nonspecific symptoms like abdominal pain, fever, nausea, and a change in bowel habit. In particular, the distinction between inflammatory bowel disease and intestinal tuberculosis remains challenging.

Case presentation

A 27-year-old man from Colombia presented with fever, night sweats, and progressive lower abdominal pain. Computed tomography revealed a thickening of the bowel wall with a mesenterial lymphadenopathy, ascites ,and a pleural tumor mass. Histology of intestinal and pleural biopsy specimens showed a granulomatous inflammation. Although microscopy and polymerase chain reaction (PCR) for Mycobacterium tuberculosis (MTB) were negative, empirical MTB treatment was initiated on suspicion. Due to a massive post-stenotic atrophied intestinal bowel, MTB medications were administered parenterally in the initial phase of treatment to guarantee adequate systemic resorption. The complicated and critical further course included an intra-abdominal abscess and bowel perforation requiring a split stoma, before the patient could be discharged in good condition after 3 months of in-hospital care.

Conclusions

This case highlights the clinical complexity and diagnostic challenges of intestinal MTB infection. A multidisciplinary team of physicians should be sensitized to a timely diagnosis of this disease, which often mimics inflammation similar to inflammatory bowel disease, other infections, or malignancies. In our case, radiological findings, histological results, and migratory background underpinned the suspected diagnosis and allowed early initiation of tuberculostatic treatment.

Image-Based Molecular Phenotyping of Pancreatic Ductal Adenocarcinoma

To bridge the translational gap between recent discoveries of distinct molecular phenotypes of pancreatic cancer and tangible improvements in patient outcome, there is an urgent need to develop strategies and tools informing and improving the clinical decision process. Radiomics and machine learning approaches can offer non-invasive whole tumor analytics for clinical imaging data-based classification. The retrospective study assessed baseline computed tomography (CT) from 207 patients with proven pancreatic ductal adenocarcinoma (PDAC). Following expert level manual annotation, Pyradiomics was used for the extraction of 1474 radiomic features. The molecular tumor subtype was defined by immunohistochemical staining for KRT81 and HNF1a as quasi-mesenchymal (QM) vs. non-quasi-mesenchymal (non-QM). A Random Forest machine learning algorithm was developed to predict the molecular subtype from the radiomic features. The algorithm was then applied to an independent cohort of histopathologically unclassifiable tumors with distinct clinical outcomes. The classification algorithm achieved a sensitivity, specificity and ROC-AUC (area under the receiver operating characteristic curve) of 0.84 ± 0.05, 0.92 ± 0.01 and 0.93 ± 0.01, respectively. The median overall survival for predicted QM and non-QM tumors was 16.1 and 20.9 months, respectively, log-rank-test p = 0.02, harzard ratio (HR) 1.59. The application of the algorithm to histopathologically unclassifiable tumors revealed two groups with significantly different survival (8.9 and 39.8 months, log-rank-test p < 0.001, HR 4.33). The machine learning-based analysis of preoperative (CT) imaging allows the prediction of molecular PDAC subtypes highly relevant for patient survival, allowing advanced pre-operative patient stratification for precision medicine applications.

Überführung von 1-Benzylisochinolinen in Berbinium-Salze

The syntheses of the dibenzoquinolizinium-salts 3, 13, 16, 20 and 25 which are of spectroscopic interest are described. Their electronic excitation spectra will be published later by Perkampus and coworkers in this journal

Multiple internalization pathways of polyelectrolyte multilayer capsules into mammalian cells

Polyelectrolyte multilayer (PEM) capsules are carrier vehicles with great potential for biomedical applications. With the future aim of designing biocompatible, effective therapeutic delivery systems (e.g., for cancer), the pathway of internalization (uptake and fate) of PEM capsules was investigated. In particular the following experiments were performed: (i) the study of capsule co-localization with established endocytic markers, (ii) switching-off endocytotic pathways with pharmaceutical/chemical inhibitors, and (iii) characterization and quantification of capsule uptake with confocal and electron microscopy. As result, capsules co-localized with lipid rafts and with phagolysosomes, but not with other endocytic vesicles. Chemical interference of endocytosis with chemical blockers indicated that PEM capsules enter the investigated cell lines through a mechanism slightly sensitive to electrostatic interactions, independent of clathrin and caveolae, and strongly dependent on cholesterol-rich domains and organelle acidification. Microscopic characterization of cells during capsule uptake showed the formation of phagocytic cups (vesicles) to engulf the capsules, an increased number of mitochondria, and a final localization in the perinuclear cytoplasma. Combining all these indicators we conclude that PEM capsule internalization in general occurs as a combination of different sequential mechanisms. Initially, an adsorptive mechanism due to strong electrostatic interactions governs the stabilization of the capsules at the cell surface. Membrane ruffling and filopodia extensions are responsible for capsule engulfing through the formation of a phagocytic cup. Co-localization with lipid raft domains activates the cell to initiate a lipid-raft-mediated macropinocytosis. Internalization vesicles are very acidic and co-localize only with phagolysosome markers, excluding caveolin-mediated pathways and indicating that upon phagocytosis the capsules are sorted to heterophagolysosomes.

Intrahepatic distribution of human glutathione-dependent formaldehyde dehydrogenase

By means of a microelectrophoretic separation technique the different forms of alcohol dehydrogenase can be detected in microdissected liver tissue samples of the nanogram range. Alcohol dehydrogenase 3 (the glutathione-dependent formaldehyde dehydrogenase) was demonstrated to be zonally distributed in the human liver parenchyma. A periportal/perivenous gradient is evident in both sexes, however, the periportal/perivenous ratio is higher in males. The biological functions of this enzymatic form and the possible role of the periportal maximum are discussed.

Changes in the activity of alcohol dehydrogenase isoenzymes during the estrus cycle in the vagina of the rat

In rodents, the vaginal epithelium undergoes cyclical changes with an alternating pattern of keratinization and mucification. It has been known for decades that vitamin A and its active form retinoic acid are responsible for normal epithelial homeostasis. However, it has not so far been certain which enzymes catalyze the first and rate-limiting step in retinoic acid synthesis. By means of microdissection and ultrathin-layer gel electrophoresis, alcohol dehydrogenase isoenzyme activity was determined quantitatively in the various layers of the vaginal mucous membrane. It was found that, in the rat, only alcohol dehydrogenase 3 and 4 are expressed. Marked cyclical changes of alcohol dehydrogenase 4 activity in the stratum germinativum of the vaginal epithelium strongly support the assumption that this isoenzyme is responsible for retinoic acid synthesis, and that it is essential for the changes accompanying keratinization and mucification.

Spatial distribution of human liver aldehyde dehydrogenase isoenzymes

To elucidate the pattern of lesions in the liver parenchyma after ethanol ingestion, the quantitative distribution profiles of both the cytosolic and the mitochondrial aldehyde dehydrogenase isoenzyme activities were determined by the use of ultrathin-layer electrophoresis. It was found that in human liver parenchyma, both isoforms of aldehyde dehydrogenase are almost homogeneously represented in the liver acinus. These quantitative data are supported by the results of an improved histochemical technique. Moreover, sex differences were not detected either in activity or in the distribution pattern. Consequently, it can be assumed that it is not the activity of total aldehyde dehydrogenase or its isoforms which is responsible for the higher susceptibility of the perivenous zone to alcohol-dependent damage.

Distribution of alcohol dehydrogenase isoenzymes in the human liver acinus

By the use of a newly developed technique of ultrathin-layer electrophoresis, class I and class II alcohol dehydrogenase activity could be demonstrated in microdissected samples of the periportal, intermediate, and perivenous zones of the liver acinus in men and women. It could be demonstrated that both classes exhibit low activity in the periportal zone. From there, a rising gradient in the direction of the perivenous end was apparent. This increase, however, was found to be significant only in women. The analysis of class I alcohol dehydrogenase isoenzymes showed that the expression of alpha-, beta-, and gamma-containing isoforms did not differ in relation to the intraacinar position. The constant proportions of the isoenzymes to the maxima and minima of the total alcohol dehydrogenase activity support the view that the adult liver-specific isoenzyme pattern is determined during postnatal development.

Studies on the vasa vasorum of the human renal artery

The transplantation of a donor kidney is currently the treatment of choice for terminal renal insufficiency. However, major postoperative problems may be caused by vascular complications. It was therefore decided to look for possible correlations between these vascular problems and the arterial wall supply. The following methods were used to elucidate the origin and distribution of nutrient vessels: 1. Injection of the abdominal aorta with resin in three fresh cadavers. 2. The precise microscopic location of the branches originating from the renal arteries in eighteen autopsy subjects. 3. Abdominal angiography and selective angiography of the first left lumbar artery and left renal artery in one patient. It was found that the renal artery receives its blood supply from both internal and external nutrient vessels. The external vascular supply of the renal arterial wall originates from the aorta itself, from the inferior suprarenal artery (which sometimes has connections with the first and/or second lumbar artery) or from the diffuse vascular system of the retroperitoneal space. Because of the variety in number, course and origin of these nutritional vessels, an ideal point for the anastomosis of the renal artery cannot be indicated.

Ultrathin-layer zone electrophoresis of alcohol dehydrogenase in partly rehydrated polyacrylamide gels: an alternative to starch gel electrophoresis

A highly sensitive electrophoretic technique for the separation of alcohol dehydrogenase isoenzymes by zone electrophoresis in partly rehydrated polyacrylamide gels is described. Five hundred microm thin polyacrylamide gels are polymerized under standardized conditions. After polymerization the gels are washed thoroughly with distilled water to remove any unreacted monomers, catalysts or still soluble polymers. The washed gels are then impregnated with 0.5% Tween 20 and dried. Before electrophoresis the dry gels are rehydrated to a thickness of 250 microm, which makes up 50% of the original gel volume. Rehydration is carried out by use of a degassed buffer solution. This method permits the demonstration of the isoenzymes of alcohol-dehydrogenase class I and II in man and allows quantitative determination.

The lymphatics of the liver

An overview of our current knowledge of the hepatic lymph vessels is given, and the different lymph node stations that are related to the liver are described. The lymphatics of the liver itself can be divided into a superficial and a deep system. The superficial vessels are mainly situated in the liver capsule, the deep ones follow the triads of Glisson or the efferent hepatic veins. There are no direct communications between spaces in the liver parenchyma and the first lymphatic capillaries, which end blindly in the surrounding connective tissue. Nevertheless, the perisinusoidal space of Disse, the space of Mall, directly adjacent to the outer limiting plate of the parenchyma, and the space of Comparini, surrounding the sublobular hepatic veins can be regarded as prelymphatic spaces from which the hepatic lymph could originate. The extracellular matrix in the space of Disse is apparently continuous with the extraparenchymal areas of the connective tissue. Collagens and proteoglycans offer a morphological pathway for the transport of fluid, the physiological prerequisites of which are discussed.

Intra-acinar profiles of cytosolic and mitochondrial malate dehydrogenase isoenzymes in rat liver

A new method for electrophoretic separation of the isoforms of malate dehydrogenase in microdissected tissue samples was applied to rat liver. The intra-acinar activity profiles of cytosolic (cMDH) and mitochondrial (mMDH) malate dehydrogenase were determined in male and female control animals and in animals fasted for 84 hr. Measurements were carried out on lyophilized liver tissue samples of 50-100 ng from the whole length of the sinusoid. The results showed that both in fed and fasted animals, mMDH activity was almost evenly distributed throughout the acinus in livers of both sexes. cMDH showed higher activity in the periportal area compared with the perivenous area by a factor of approximately 1.35 in all animals studied. Our results favor a slightly higher capacity of the malate-aspartate shuttle in the periportal area in both fed and fasted animals. Furthermore, the distribution pattern of mMDH suggests that this isoenzyme is not a marker for the zonation of the oxidative metabolism in the liver acinus.

Microquantitative determination of lactate dehydrogenase isoenzymes in the myocardium and the conducting system

A newly developed technique was used for the electrophoretic separation of lactate dehydrogenase (LDH) isoenzymes from lyophilized tissue samples in the nanogram range. In this study portions of 10-200 ng from the myocardium and the conducting system of cattle, sheep, pig and man were microdissected and analysed. In the heart tissues of cattle, sheep and pig, the isoforms LDH1, LDH2 and LDH3 were detected in species-specific varying amounts. In all these animals, the conducting system is marked by high LDH1 activity, which is present at a ratio of about 2:1 compared with the myocardium. The values in man, however, differ from these values, but this might be due to post-mortem changes. The findings are discussed with respect to possible aerobic-anaerobic functions.

Ultrathin-layer microelectrophoretic determination of lactate dehydrogenase isoenzymes in corneal and conjunctival epithelium of the cow

In order to evaluate the impact of tissue oxygenation on the distribution pattern of lactate dehydrogenase isoenzymes, activities of the isoenzymes were measured in microdissected samples of bovine tissue. A highly sensitive ultrathin-layer electrophoretic technique was used to determine the distribution pattern of lactate dehydrogenase isoenzymes in basal, intermediate and superficial layers of the epithelium of central and peripheral cornea and in the epithelium of the bulbar conjunctiva. Measurements revealed almost homogeneous intraepithelial distribution patterns of lactate dehydrogenase isoenzymes in both tissues. In the cornea the lactate dehydrogenase isoenzymes 4 and 5, which are regarded to be specialized for anaerobic glucose metabolism, were found to predominate. In the well-oxygenated conjunctival epithelium most of the activity could be ascribed to the lactate dehydrogenase isoenzyme 3. In contrast to the isoenzymatic activities, total activity of lactate dehydrogenase was inhomogeneously distributed; maximum activities were found in the basal layer of corneal epithelium and in the intermediate layer of conjunctival epithelium. The results indicate that oxygen supply is relevant rather for the intraepithelial distribution of total enzyme activity than for the expression of lactate dehydrogenase isoenzymes.

The intramucosal distribution of gastric alcohol dehydrogenase and aldehyde dehydrogenase activity in rats

Using qualitative and microquantitative histo-chemical techniques, alcohol dehydrogenase and aldehyde dehydrogenase activity was studied in the gastric mucosa of male and female rats. Alcohol dehydrogenase was demonstrated by staining reactions with maximum activity in surface and neck cells and with clearly weaker activity also in parietal cells. Aldehyde dehydrogenase could be detected in surface and neck cells, and also to a comparable degree in the parietal cells. Quantitative analyses of microdissected samples yielded high values for alcohol dehydrogenase activity exclusively in the superficial part of the gastric mucosa, whereas low-Km aldehyde dehydrogenase activity showed a decreasing gradient from the surface to the deeper parts of the mucosa. Sex differences could not be confirmed.

Liver architecture

The development of liver parenchyma starts from entodermal cells which grow out from the gut into the mesenchyma of the septum transversum. In the definitive organ this close association of epithelial cells (hepatocytes) and mesenchyma-derived nonparenchymal cells is maintained. The liver, and with it each hepatocyte, acts in two directions: the vascular poles of the hepatocytes serve in an ingestive sense, while at their biliary poles secretory functions are exerted. Hepatic microvascularization comprises two afferent vessels (arterial and portal terminal branches), the sinusoids and the terminal hepatic venule. Sinusoidal cells surround the capillaries but also have highly specialized functions with regard to filtration, phagocytosis, fat storage and defense. The autonomic innervation plays an important role in the regulation of metabolic functions. Above the cellular level the proper architecture of the liver parenchyma has been the object of controversial discussions for centuries. The concept of the liver lobule, the portal unit, the liver acinus and other structures are presented and discussed. Finally, the liver parenchyma is described as an irregular interdigitating system of regions related to the terminal blood vessels.

Intraacinar profiles of alcohol dehydrogenase and aldehyde dehydrogenase activities in human liver

The intraacinar activity profiles of alcohol dehydrogenase and the aldehyde dehydrogenases (I, I plus II, and total) were determined, using liver biopsy samples from eight male and eight female patients. Microchemical assays were performed in microdissected tissue samples from the whole length of the sinusoid. Alcohol dehydrogenase activity in men less than 53 years of age showed a maximum in the intermediate zone, whereas in women less than 50 years of age an increase in the gradient toward the perivenous zone was observed. Furthermore, alcohol dehydrogenase activity in the livers of women was significantly higher than in men. After the age of 53 in men and 50 in women, the sex specificity of the distribution profiles was no longer apparent. The intraacinar profiles of aldehyde dehydrogenase isoenzymes showed only minor variations in the different groups; they were not statistically significant. This is also true for low-Michaelis constant (Km) aldehyde dehydrogenase, which is most important for acetaldehyde oxidation in vivo. Thus, of the variations in zonal heterogeneity of ethanol-degrading enzymes, it is mainly the activity of alcohol dehydrogenase that may contribute to the sex- and age-related susceptibility of liver parenchyma.

Microquantitative analysis of the intra-acinar profiles of glutamate dehydrogenase in rat liver

In adult male and female rat liver, the activity of NAD(+)-and NADP(+)-dependent glutamate dehydrogenase (GDH) was microquantitatively measured in tissue samples of 50-150 ng, microdissected continuously along the sinusoidal length. Total activity of GDH with NAD+ as co-factor was found to be higher by a ratio of about 1:2.3 than with NADP+. All intra-acinar enzyme profiles, irrespective of sex, showed an increasing gradient of GDH activity from the periportal beginning to the perivenous end. These findings are at variance with the immunohistochemical localization of GDH in rat liver. The microquantitative GDH profiles with higher perivenous values could indicate a more pronounced glutamine synthesis in Zone 3 of the liver acinus.

Changes in activity and intra-acinar distribution of glucose-6-phosphate dehydrogenase and malic enzyme during pregnancy in rat liver

Using techniques of microdissection and microassay as well as qualitative histochemistry the activity and intra-acinar distribution of G6PDH and ME were studied on selected days of pregnancy in the rat. Both enzymes show distinct fluctuations during the course of pregnancy in keeping with changes in hepatic lipogenesis. Marked increases in activity are seen as early as the 4th day, while highest values are attained on day 20, with a predominant perivenous induction. On day 22, just before parturition a sharp decrease of both enzyme activities with a flattening of the periportal/perivenous gradient was detected. G6PDH shows proportionally considerably larger increases and more distinct changes in zonation. The perivenous fluctuations in G6PDH activity of late gestation are supposed to be caused primarily by insulin. Although estrogen is known to induce both enzymes, the temporal changes in enzyme activity in pregnancy cannot be related to the action of estrogen alone. The changes in enzyme activity, however, correspond well to those of progesterone, and although no direct action of progesterone on these enzymes has yet been proposed, further work on its effects on enzyme activity and distribution is indicated.

The circadian rhythm of intra-acinar profiles of alcohol dehydrogenase activity in rat liver: a microquantitative study

Using microquantitative measurements of alcohol dehydrogenase activity in microdissected samples of liver tissue along the sinusoidal length, the intra-acinar distribution profiles were studied in seven groups of female rats at different times during 24 h with a light phase from 6:30 h to 18:30 h. The mean values of alcohol dehydrogenase activity showed a circadian rhythm with a minimum at 13.30 h and a maximum at 17.30 h (p less than 0.001). However, the intra-acinar gradients remained almost unchanged, indicating that increase and decrease in enzyme activity takes place simultaneously in all parts of the liver acinus. This observation, together with data from the literature, suggests that the circadian rhythm of alcohol dehydrogenase activity reflects variations in different liver cell constituents, rather than enzyme protein synthesis or proteolysis.

Nutritional and gonadal effects on the intra-acinar profiles of low-Km and high-Km aldehyde dehydrogenase activity in rat liver

Total and low-Km aldehyde dehydrogenase (ALDH) activity was measured in 50-150 ng microdissected liver tissue samples of the entire sinusoidal length. High-Km ALDH activity was calculated by subtracting the low-Km ALDH values from the total ALDH activity. Enzyme activity was measured by a microchemical assay, using the oil-well technique with luminometric determination of NADH. The intra-acinar profiles of high-Km and low-Km ALDH activity could be demonstrated graphically for both male and female rats after 84 h of starvation, and after starvation and refeeding for 6 nights. In addition, the ALDH distribution patterns of juvenile, castrated, and castrated and testosterone-treated rats were determined. It could be demonstrated that starvation, and starvation followed by refeeding, lead to changes in enzyme activity which parallel the loss and regain of liver- and body-weight. The nutritional factors do not essentially alter the normal intra-acinar profiles. In juvenile rats, ALDH is lower by 30% in comparison with the controls, but sex-differences in the distribution profiles are not yet present. Castration has no effect on the amount of enzyme activity but the sex specific distribution profiles are less marked. The main effect of testosterone treatment is an elevation of low-Km ALDH in the perivenous zone. The characteristics of the intra-acinar profiles of high-Km and low-Km ALDH activity are discussed with respect to hepatic acetaldehyde oxidation and alcoholic liver damage.

Microquantitative determination of intra-acinar distribution profiles of low-Km and high-Km aldehyde dehydrogenase activity in rat liver

Microquantitative measurements of total and of low-Km aldehyde dehydrogenase (ALDH) activity with millimolar and micromolar concentrations of acetaldehyde and propionaldehyde were carried out on the livers of male and female rats. Lyophilized cryostat sections of liver parenchyma were microdissected along the entire sinusoidal length from the terminal afferent vessels to the terminal efferent venule. ALDH activity was measured in a microbiochemical assay using the oil-well technique with luminometric determination of NADH. On the basis of single measurements, mean values of total, low-Km and high-Km ALDH activity could be calculated and the specific distribution patterns graphically demonstrated. The two substrates acetaldehyde and propionaldehyde yielded similar values of ALDH activity, the intraacinar distribution profiles of which showed characteristic sex differences. In the liver of the male rat high-Km ALDH activity has two flat peaks in the periportal and the perivenous area, while low-Km ALDH activity is almost evenly distributed throughout the acinus. In the livers of female rats, both high-Km and low-Km ALDH activity shows a continuous gradient which decreases from the periportal to the perivenous zone (pp/pv = 1.4:1). It was therefore possible to demonstrate that the maxima of alcohol dehydrogenase activity and of low-Km ALDH activity are localized in opposite parts of the liver acinus of the female rat. This heterotopy should have consequences with respect to hepatotoxicity after alcohol ingestion.

The intra-acinar distribution patterns of alcohol-dehydrogenase activity in the liver of juvenile, castrated and testosterone-treated rats

Rat liver alcohol dehydrogenase shows characteristic sex-differences with respect to activity and heterotopy. For the recognition of gonadal influences on the intra-acinar distribution patterns luminometric determinations of ADH activity were carried out on 50-150 ng lyophilized liver tissue samples which had been microdissected along the sinusoidal length. Juvenile rats of both sexes showed equally high alcohol dehydrogenase activity, which surpassed the adult values by a factor of 2 in males and 1.3 in females. The distribution pattern was rather flat, with a weak maximum at the beginning of the last third of the sinusoid. Castration of adult male and female rats resulted in an increase of alcohol dehydrogenase activity to around the prepubertal values. The intra-acinar profiles showed a gradual increase in activity from low periportal values to a peak near the perivenous zone. Only the hepatocytes directly adjacent to the efferent venule showed an even lower activity. Administration of testosterone to castrated animals had no effect on the ADH activity in males and resulted in only a slight decrease of enzyme activity in females. The intra-acinar distribution patterns showed an intermediary peak at the end of the second third of the sinusoidal length in males and a gradual increase of activity, beginning periportally, in the direction of the perivenous zone in females. The present findings on total activity of ADH and its distribution patterns in the liver are considered to be the result of complex hormonal alterations rather than a specific effect of testosterone.

The effects of starving and refeeding on the intra-acinar distribution pattern of alcohol-dehydrogenase activity in rat liver

Microquantitative determinations of ADH activity were carried out on the livers of male and female rats. The animals were either starved for 84 h, or starved and then refed with a carbohydrate-rich diet for 6 nights. When the enzyme activity is expressed in mumoles/min/g dry weight, fasting does not appear to alter liver ADH activity, while in starved and subsequently refed rats it is diminished by 20%. Microquantitative measurements of ADH activity in 50-150 ng lyophilized tissue samples, microdissected the whole way along the sinusoidal length, made the computer-aided plotting of intra-acinar distribution patterns possible. The results showed that, under the feeding conditions selected, only minor changes in the ADH activity profiles occur in the liver acinus. These are within the range of the standard deviations of the normal mean values. From these results it can be deduced that fasting and refeeding do not lead to specific inhibition or induction of liver ADH activity. - The decrease of ADH activity of total liver (mumol/min) per total body weight in starved rats is obviously the result of a loss of protein which affects the liver cells of all acinar zones almost equally.

Microquantitative determination of the distribution patterns of alcohol dehydrogenase activity in the liver of rat, guinea-pig and horse

Microquantitative measurements of ADH-activity were carried out on the livers of male and female rats, guinea-pigs and horses (two geldings and a mare). Lyophilized cryostat sections of liver parenchyma were microdissected the whole way along the sinusoidal length from the terminal afferent vessels to the terminal efferent venule. ADH activity in samples of about 50-150 ng was measured in a microbiochemical assay using the oil-well technique without enzymatic cycling, by direct luminometric determination of NADH. On the basis of the single measurements, mean values of total hepatic ADH activity could be calculated and the specific distribution patterns graphically demonstrated. Total activity of ADH in the liver of the female rat is 1.6 times higher than in the male; the male distribution pattern exhibits a relative maximum in the intermediary zone of the acinus while the activity in the liver of female rats increases towards a perivenous maximum. Mean values for total ADH activity in the livers of male and female guinea-pigs are almost equal and there is, moreover, no clear intra-acinar gradient. Mare and castrated male horses show high hepatic ADH activity which is evenly distributed in the liver acinus.

The relation of rat liver wet weight to dry weight

To assess a reliable relation between the dry and wet weight of rat livers, the water content of liver samples was determined by freeze drying. The ratio between wet and dry weight of the livers turned out as 3.33 +/- 0.3 for male and 3.28 +/- 0.24 for female rats. Thus for calculations a value of 3.3 can be used irrespective of the sex of rats.

Histochemical studies on metabolic zonation of the liver in the trout (Salmo gairdneri)

The livers of 26 adult male and female trout were studied histochemically. G6Pase activity was always found to be heterotopically distributed with a constant maximum in the periportal area. In many cases the glycogen content and the activity of phosphorylase predominated in the periportal zone as well. Maximum activity of glucose-6-phosphate-dehydrogenase and malic enzyme, however, could be demonstrated preferentially in the perivenous area. Lactate dehydrogenase, succinate dehydrogenase, alcohol dehydrogenase, acid phosphatase and beta-glucuronidase were found equally in all liver cells. 3-Hydroxybutyrate dehydrogenase was absent. Thus, the principles of metabolic zonation have been established in trout liver, the architecture of which differs essentially from that of mammals. The course of the terminal afferent and efferent vessels is the decisive factor for the heterotopic localization of functional units rather than the tubular or plate-forming arrangement of the hepatocytes.

Antagonistic reaction of the periportal and perivenous zone in the rat liver after castration and estrogen treatment. Histochemical and biochemical studies on G6PDH and malic enzyme activity

G6PDH and ME activity was determined biochemically in homogenates and demonstrated histochemically in cryostat sections of rat liver. Control animals were sham-operated, the male and female rats of the experimental groups were castrated. After castration groups of rats were treated with daily doses of 3 or 6 micrograms/estradiol benzoate for 21 days. The results show that in the controls there is a sex-dependent distribution pattern of the two enzymes; in males the rather low activity is mainly located in the periportal area, in females the higher activity is demonstrable in the perivenous area. After castration G6PDH activity (and to a lesser extent ME activity) increases, mainly in the periportal zone. Estrogen treatment results in the high activity of both enzymes, which are exclusively located in the perivenous zone. In the periportal zone no G6PDH or ME activity is demonstrable histochemically. This zone-typical effect of estrogen is interpreted in terms of the concept of Metabolic Zonation, according to which it is supposed that the NADPH generating enzymes in the perivenous area have a lipogenic function whereas the periportal activity contributes to bile acid production.

A technical note on the histochemical demonstration of G6Pase activity

Difficulties in the histochemical demonstration of even maximum G6Pase activity can be overcome when unfixed cryostat sections are immersed in a medium which is shaken during incubation. The medium contains: 20mM G6P, 4.6 mM Pb(NO3)2, 50 mM tris-maleate buffer, pH 6.5.

The glucose/glucose-6-phosphate cycle in the periportal and perivenous zone of rat liver

Periportal and perivenous hepatocytes contain different activities (V) of antagonistic key enzymes such as glucokinase and glucose-6-phosphatase. In order to get an insight into the metabolism of the periportal and perivenous area the flux rates (v) of the glucose/glucose-6-phosphate cycle were calculated on the basis of the Michaelis-Menten equation using the measured zonal concentrations of glucose and glucose 6-phosphate, the zonal activities of glucokinase and glucose-6-phosphatase previously reported and the half-saturating substrate concentrations (Km) of the two enzymes found in the literature. The concentrations of glucose were obtained as a first approximation by measuring the concentrations in portal (= periportal) and hepatovenous (= perivenous) blood; those of glucose 6-phosphate were calculated from the levels determined in microdissected periportal and perivenous liver tissue. The calculations showed (a) that the overall cycling rates agreed remarkably well with those reported for intact animals and (b) that during a normal feeding rhythm the periportal zone should catalyze net glucose output and the perivenous zone should mediate net glucose uptake, as proposed by the model of 'metabolic zonation'.

Postnatal differentiation of sex-specific distribution patterns of G6Pase, G6PDH and ME in the rat liver

The activity of the liver enzymes G6Pase, G6PDH and ME was studied in rats of 2-9 weeks old by histochemical means. In addition, G6PDH and ME activity was quantitatively determined in homogenates. In the 2nd and 3rd week G6Pase is similarly distributed in both sexes: while in the periportal zone high activity is demonstrable, the perivenous zone shows only low activity. After this period a nearly homogeneous distribution pattern becomes evident in all animals. Sex difference occurs after the 6th week: in the livers of male rats the periportal "maximum" is sometimes combined with a second peak in the perivenous area, in females a steep gradient emerges with high activity in the periportal zone and a low one in the perivenous zone. In the first postnatal weeks G6PDH activity is very low in parenchymal cells, but very prominent in Kupffer cells. Around the 5th week there is an increase, predominantly in the perivenous zone of both sexes. While there is again a further decrease demonstrable in male rats, the G6PDH activity of female rats rises to high adult values. This increase seems to be restricted to the perivenous zone. ME can be demonstrated at first in leucocytes. In the course of the 3rd week there is an increase of activity in both sexes: ME is demonstrable in parenchymal cells of the perivenous area and in scattered hepatocytes of the periportal area. In male rats, the perivenous activity is diminished towards the end of the investigation period, in females, however, a high activity remains in the perivenous zone. The data show that in females the activity of NADP dependent enzymes is high in the perivenous zone, so it may be assumed that a lipogenic area is situated around the terminal efferent vessels. Because of the sex difference this area may be hormone-dependent. The lipogenic area is situated opposite to the gluco(neo)genic area which corresponds to the periportal zone.

Quantitative topography of organelles in the liver. A combined histochemical and morphometric analysis

After seven days of feeding fructose the liver of Wistar rats showed enormous accumulations of glycogen, which completely altered the original pattern of distribution of organelles. A quantitative morphological method was used to analyze these changes. The cytoplasm was mapped into arbitrary "distance classes" corresponding to concentric rings beginning at the outer nuclear membrane. This allowed the density of organelles in a given zone to be estimated. In cells filled with glycogen as a result of the fructose feeding, the following rearrangements were found: in the intermediate zone of both cellular poles (i.e., bile canalicular pole and sinusoidal pole) the mitochondria disappeared, being replaced by glycogen. The endoplasmic reticulum was accumulated in the perinuclear zone of both cellular poles, as in control animals, but was reduced throughout the rest of cytoplasm. It showed a peripheral density maximum at the biliary canalicular pole, in contrast to the cells of control animals. These changes in the distribution of the organelles and cellular "compartments" correspond to histochemical findings and demonstrate an adaptive reaction in the liver parenchyma to fructose ingestion, the organelles arranging themselves in cytoplasmic regions which still show a metabolic activity.

Metabolic zonation in thioacetamide-induced liver cirrhosis

After TAA administration to rats a central part may be distinguished histochemically from a marginal part in most of the cirrhotic nodules. The centre is characterized by a high glycogen content and by high activity of phosphorylase, G6Pase and SDH; the maxima of which are situated around the larger blood vessels. The vasculatory periphery, however, shows moderate G6PDH-activity. The marginal parts of the nodules are poor in glycogen and possess only weak G6Pase and phosphorylase activity, whereas high SDH- and G6PDH-activity can be demonstrated here. This distribution pattern leads to the conclusion that the larger blood vessels in the centre of the nodules are themselves the terminal afferent vessels. Thus the centre of the nodule corresponds to periportal zone 1, while G6PDH-activity marks the area corresponding to zone 3. The fact that the marginal parts of the nodules are marked by high SDH- but weak G6Pase-activity is interpreted as the result of a preferential arterial supply to this parenchymal part. The high G6PDH-activity of the marginal part is seen in context with the regeneration processes. In all animals single nodules could be found with a high glycogen content and extremely high G6PDH-activity. This loss of heterogeneity is interpreted as a first step in the direction of malignancy.

The development of functional heterogeneity in the liver parenchyma of the golden hamster

Prenatal and postnatal stages of the development of golden hamsters were studied histochemically and biochemically. It was shown that, beginning with the 12th gestational day, the fetal liver starts to store glycogen, and that this process reaches its maximum a birth. Glycogen phosphorylase and glucose-6-phosphatase (G6Pase)-activity increased drastically in the last two days before birth, glycogen phosphorylase preceding G6Pase. As a histochemical characteristic, an even distribution of glycogen, glycogen phosphorylase and G6Pase activity is found in the liver parenchyma at birth. During the first two postnatal weeks typical heterogeneous patterns of distribution developed: glycogen depletion could be demonstrated predominantly in zone 1 of the liver acinus, this being at the same time the area of highest glycogen phosphorylase and G6Pase-activity. The periportal zone 1 thus became characterized as the primary site of glycogenolysis (glycogen phosphorylase) and gluco(neo)genesis (G6Pase). "Metabolic Zonation" is interpreted as the chemomorphological equivalent of the regulatory function of the liver as a glucostat.

Histochemical studies on carbohydrate metabolism in rat liver after galactosamine administration

The development of hepatitis, induced in 48 rats by the administration of galactosamine (GalN) in varying doses, was studied with the use of substrate and enzyme histochemical techniques. The so-called atypical glycogen, which is at first highly resistant to diastase, was shown to be digestible after deamination. The increasing accumulation of atypical glycogen during the course of GalN-hepatitis conceals the loss of normal glycogen when the PAS-reaction is used. Nevertheless glycogenolysis could also be demonstrated by the increasing activity of phosphorylase. The acid phosphatase activity was progressively diminished, which was interpreted as signifying early lysosomal damage. G6Pase activity remained nearly constant but SDH showed a decrease in activity after 12 h. These histochemical results are considered to provide deeper insight into the pathological mechanism of GalN-hepatitis.

Identification of G6PDH-active sinusoidal cells as Kupffer cells in the rat liver

The aim of this study was to identify the G6PDH-active sinusoidal cells in the rat liver described by Rieder et al. (1978). Because of their number and distribution in the liver parenchyma, endothelial cells and pit cells could be excluded. Fat-storing cells were specifically marked by vital staining with vitamin A and identified by fluorescence microscopy. Kupffer cells could be detected after vital staining with carmine. Both staining methods allowed a subsequent incubation for the demonstration of G6PDH activity in the same unfixed cryostat section. Whereas more than 80% of the fluorescent particles were found outside the enzyme-positive cells, all G6PDH-active cells contained carmine particles. After counting the G6PDH-active cells, an estimation of 0.217 x 10(8) cells/g liver tissue was obtained. The results indicate that high G6PDH activity is common to all Kupffer cells, and is therefore a highly specific marker enzyme for this class of sinusoidal liver cells.

Increase of the gluconeogenic and decrease of the glycolytic capacity of rat liver with a change of the metabolic zonation after partial hepatectomy

During the first 72 h after 67% partial hepatectomy of female Wistar rats (160 g) the specific activities [mumol X min-1 X (g liver)-1] of the glucogenic glucose-6-phosphatase and fructose-bisphosphatase and of the glycolytic hexokinase and 6-phosphofructokinase remained essentially constant. However, the activity of the glycolytic pyruvate kinase (L- plus M2-type) was decreased slightly and that of glucokinase was decreased markedly to below 30%, while the glucogenic phosphoenolpyruvate carboxykinase was increased to over 200%. Between 10 and 40 h after partial hepatectomy, when the proliferation started in the periportal area, a shift of the glucogenic glucose-6-phosphatase-rich zone from its normal periportal to an intermediate or even perivenous position was observed histochemically. After 48 h, when the proliferation was no longer restricted to the periportal zone, the normal glucose-6-phosphatase zonation (as before partial hepatectomy) was restored. Glycogen was degraded rapidly during the first 4 h after operation; it was later repeatedly resynthesized and degraded in correlation with the feeding rhythm of the animals. The zonation of glycogen metabolism was in accord with the observed zonation of glucose-6-phosphatase.

NADP-dependent dehydrogenases in rat liver parenchyma. I. Methodological studies on the qualitative histochemistry of G6PDH, 6PGDH, malic enzyme and ICDH

At present soluble NADP-dependent dehydrogenases are histochemically demonstrated in three different ways: according to the standard method incubation in aqueous media leads to the precipitation of formazan, the formation of which depends entirely on the presence of endogeneous NADPH2-tetrazolium reductases. With the two more recently established methods these reductases are by-passed with the use of intermediate electron acceptors incorporated in the medium. In addition, enzyme diffusion is inhibited either by an increased viscosity of the medium (PVA) or by a semipermeable membrane separating the medium from the section. Depending on the technique applied different distribution patterns have been described. By altering the concentrations of substrates, coenzyme, tetrazolium salt and cytochrome oxidase inhibitor, it was possible to improve both the PVA and membrane methods. Although similar results were obtained, because of its advantages the PVA method is recommended in this report and a detailed description is given. Using the latter for the demonstration of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), malic enzyme (ME) and isocitrate dehydrogenase (ICDH), characteristic distribution patterns were obtained in the liver parenchyma of male and female rats. For the first time a high G6PDH activity could be demonstrated in nonparenchymal cells which are mainly found in zone 1 of the liver acinus.