The connectivity-based architecture of the human piriform cortex.

The anatomy of the human piriform cortex (PC) is poorly understood. We used a bimodal connectivity-based-parcellation approach to investigate subregions of the PC and its connectional differentiation from the amygdala. One hundred (55 % female) genetically unrelated subjects from the Human Connectome Project were included. A region of interest (ROI) was delineated bilaterally covering PC and amygdala, and functional and structural connectivity of this ROI with the whole gray matter was computed. Spectral clustering was performed to obtain bilateral parcellations at granularities of k = 2-10 clusters and combined bimodal parcellations were computed. Validity of parcellations was assessed via their mean individual-to-group similarity per adjusted rand index (ARI). Individual-to-group similarity was higher than chance in both modalities and in all clustering solutions. The amygdala was clearly distinguished from PC in structural parcellations, and olfactory amygdala was connectionally more similar to amygdala than to PC. At higher granularities, an anterior and ventrotemporal and a posterior frontal cluster emerged within PC, as well as an additional temporal cluster at their boundary. Functional parcellations also showed a frontal piriform cluster, and similar temporal clusters were observed with less consistency. Results from bimodal parcellations were similar to the structural parcellations. Consistent results were obtained in a validation cohort. Distinction of the human PC from the amygdala, including its olfactory subregions, is possible based on its structural connectivity alone. The canonical fronto-temporal boundary within PC was reproduced in both modalities and with consistency. All obtained parcellations are freely available.

g-Ratio weighted imaging of the human spinal cord in vivo.

The fiber g-ratio is defined as the ratio of the inner to the outer diameter of the myelin sheath. This ratio provides a measure of the myelin thickness that complements axon morphology (diameter and density) for assessment of demyelination in diseases such as multiple sclerosis. Previous work has shown that an aggregate g-ratio map can be computed using a formula that combines axon and myelin density measured with quantitative MRI. In this work, we computed g-ratio weighted maps in the cervical spinal cord of nine healthy subjects. We utilized the 300mT/m gradients from the CONNECTOM scanner to estimate the fraction of restricted water (fr) with high accuracy, using the CHARMED model. Myelin density was estimated using the lipid and macromolecular tissue volume (MTV) method, derived from normalized proton density (PD) mapping. The variability across spinal level, laterality and subject were assessed using a three-way ANOVA. The average g-ratio value obtained in the white matter was 0.76+/-0.03, consistent with previous histology work. Coefficients of variation of fr and MTV were respectively 4.3% and 13.7%. fr and myelin density were significantly different across spinal tracts (p=3×10-7 and 0.004 respectively) and were positively correlated in the white matter (r=0.42), suggesting shared microstructural information. The aggregate g-ratio did not show significant differences across tracts (p=0.6). This study suggests that fr and myelin density can be measured in vivo with high precision and that they can be combined to produce a g-ratio-weighted map robust to free water pool contamination from cerebrospinal fluid or veins. Potential applications include the study of early demyelination in multiple sclerosis, and the quantitative assessment of remyelination drugs.

Investigations on the beam quality correction factor for ionization chambers in high-energy brachytherapy dosimetry.

Objective. To enhance the investigations on MC calculated beam quality correction factors of thimble ionization chambers from high-energy brachytherapy sources and to develop reliable reference conditions in source and detector setups in water.Approach. The response of five different ionization chambers from PTW-Freiburg and Standard Imaging was investigated for irradiation by a high dose rate Ir-192 Flexisource in water. For a setup in a Beamscan water phantom, Monte Carlo simulations were performed to calculate correction factors for the chamber readings. After exact positioning of source and detector the absorbed dose rate at the TG-43 reference point at one centimeter nominal distance from the source was measured using these factors and compared to the specification of the calibration certificate. The Monte Carlo calculations were performed using the restricted cema formalism to gain further insight into the chamber response. Calculations were performed for the sensitive volume of the chambers, determined by the methods currently used in investigations of dosimetry in magnetic fields.Main results. Measured dose rates and values from the calibration certificate agreed within the combined uncertainty (k= 2) for all chambers except for one case in which the full air cavity was simulated. The chambers showed a distinct directional dependence. With the restricted cema formalism calculations it was possible to examine volume averaging and energy dependence of the perturbation factors contributing to the beam quality correction factor also differential in energy.Significance. This work determined beam quality correction factors to measure the absorbed dose rate from a brachytherapy source in terms of absorbed dose to water for a variety of ionization chambers. For the accurate dosimetry of brachytherapy sources with ionization chambers it is advisable to use correction factors based on the sensitive volume of the chambers and to take account for the directional dependence of chamber response.

Pushing the limits of in vivo diffusion MRI for the Human Connectome Project.

Perhaps more than any other "-omics" endeavor, the accuracy and level of detail obtained from mapping the major connection pathways in the living human brain with diffusion MRI depend on the capabilities of the imaging technology used. The current tools are remarkable; allowing the formation of an "image" of the water diffusion probability distribution in regions of complex crossing fibers at each of half a million voxels in the brain. Nonetheless our ability to map the connection pathways is limited by the image sensitivity and resolution, and also the contrast and resolution in encoding of the diffusion probability distribution. The goal of our Human Connectome Project (HCP) is to address these limiting factors by re-engineering the scanner from the ground up to optimize the high b-value, high angular resolution diffusion imaging needed for sensitive and accurate mapping of the brain's structural connections. Our efforts were directed based on the relative contributions of each scanner component. The gradient subsection was a major focus since gradient amplitude is central to determining the diffusion contrast, the amount of T2 signal loss, and the blurring of the water PDF over the course of the diffusion time. By implementing a novel 4-port drive geometry and optimizing size and linearity for the brain, we demonstrate a whole-body sized scanner with G(max) = 300 mT/m on each axis capable of the sustained duty cycle needed for diffusion imaging. The system is capable of slewing the gradient at a rate of 200 T/m/s as needed for the EPI image encoding. In order to enhance the efficiency of the diffusion sequence we implemented a FOV shifting approach to Simultaneous MultiSlice (SMS) EPI capable of unaliasing 3 slices excited simultaneously with a modest g-factor penalty allowing us to diffusion encode whole brain volumes with low TR and TE. Finally we combine the multi-slice approach with a compressive sampling reconstruction to sufficiently undersample q-space to achieve a DSI scan in less than 5 min. To augment this accelerated imaging approach we developed a 64-channel, tight-fitting brain array coil and show its performance benefit compared to a commercial 32-channel coil at all locations in the brain for these accelerated acquisitions. The technical challenges of developing the over-all system are discussed as well as results from SNR comparisons, ODF metrics and fiber tracking comparisons. The ultra-high gradients yielded substantial and immediate gains in the sensitivity through reduction of TE and improved signal detection and increased efficiency of the DSI or HARDI acquisition, accuracy and resolution of diffusion tractography, as defined by identification of known structure and fiber crossing.

An implanted 8-channel array coil for high-resolution macaque MRI at 3T.

An 8-channel receive coil array was constructed and implanted adjacent to the skull in a male rhesus monkey in order to improve the sensitivity of (functional) brain imaging. The permanent implant was part of an acrylic headpost assembly and only the coil element loop wires were implanted. The tuning, matching, and preamplifier circuitry was connected via a removable external assembly. Signal-to-noise ratio (SNR) and noise amplification for parallel imaging were compared to single-, 4-, and 8-channel external receive-only coils routinely used for macaque fMRI. In vivo measurements showed significantly improved SNR within the brain for the implanted versus the external coils. Within a region-of-interest covering the cerebral cortex, we observed a 5.4-, 3.6-fold, and 3.4-fold increase in SNR compared to the external single-, 4-, and 8-channel coils, respectively. In the center of the brain, the implanted array maintained a 2.4×, 2.5×, and 2.1× higher SNR, respectively compared to the external coils. The array performance was evaluated for anatomical, diffusion tensor and functional brain imaging. This study suggests that a stable implanted phased-array coil can be used in macaque MRI to substantially increase the spatial resolution for anatomical, diffusion tensor, and functional imaging.

Improving diffusion MRI using simultaneous multi-slice echo planar imaging.

In diffusion MRI, simultaneous multi-slice single-shot EPI acquisitions have the potential to increase the number of diffusion directions obtained per unit time, allowing more diffusion encoding in high angular resolution diffusion imaging (HARDI) acquisitions. Nonetheless, unaliasing simultaneously acquired, closely spaced slices with parallel imaging methods can be difficult, leading to high g-factor penalties (i.e., lower SNR). The CAIPIRINHA technique was developed to reduce the g-factor in simultaneous multi-slice acquisitions by introducing inter-slice image shifts and thus increase the distance between aliased voxels. Because the CAIPIRINHA technique achieved this by controlling the phase of the RF excitations for each line of k-space, it is not directly applicable to single-shot EPI employed in conventional diffusion imaging. We adopt a recent gradient encoding method, which we termed "blipped-CAIPI", to create the image shifts needed to apply CAIPIRINHA to EPI. Here, we use pseudo-multiple replica SNR and bootstrapping metrics to assess the performance of the blipped-CAIPI method in 3× simultaneous multi-slice diffusion studies. Further, we introduce a novel image reconstruction method to reduce detrimental ghosting artifacts in these acquisitions. We show that data acquisition times for Q-ball and diffusion spectrum imaging (DSI) can be reduced 3-fold with a minor loss in SNR and with similar diffusion results compared to conventional acquisitions.

32-channel RF coil optimized for brain and cervical spinal cord at 3 T.

Diffusion and functional magnetic resonance imaging of the spinal cord remain challenging due to the small cross-sectional size of the cord and susceptibility-related distortions. Although partially addressable through parallel imaging, few highly parallel array coils have been implemented for the cervical cord. Here, we developed a 32-channel coil that fully covers the brain and c-spine and characterized its performance in comparison with a commercially available head/neck/spine array. Image and temporal signal-to-noise ratio were, respectively, increased by 2× and 1.8× in the cervical cord. Averaged g-factors at 4× acceleration were lowered by 22% in the brain and by 39% in the spinal cord, enabling 1-mm isotropic R = 4 multi-echo magnetization prepared gradient echo of the full brain and c-spine in 3:20 min. Diffusion imaging of the cord at 0.6 × 0.6 × 5 mm(3) resolution and tractography of the full brain and c-spine at 1.7-mm isotropic resolution were feasible without noticeable distortion. Improvements of this nature potentially enhance numerous basic and clinical research studies focused on spinal and supraspinal regions.

[Combination of radiological and nuclear medical imaging in animals: an overview about today's possibilities]. / Kombinierte radiologische und nuklearmedizinische Bildgebung in Tierexperimenten: Ein Uberblick über die aktuellen Möglichkeiten.

Molecular imaging of small animals has made considerable progress in the last years. Various research fields are interested in imaging small animals due to the lower numbers of animals per experiment. This has advantages with respect to financial, ethical and research aspects. Non-invasive imaging allows examination of one animal several times during the same experiment. This makes it possible to follow a pathological process in the same animal over time. However, the radiological methods used such as magnetic resonance imaging or computed tomography as well as the nuclear medicine methods such as single photon emission computed tomography or positron emission tomography suffer from disadvantages. Molecular aspects are limited in the radiological methods while anatomical localization is difficult in nuclear medicine. The fusion of these methods leads to additional information. This review shows today's possibilities with their advantages as well as disadvantages.

The isolation and characterization of a concanavalin A receptor from boar spermatozoa surface.

Boar spermatozoa were radioactively labeled by either lactoperoxidase-catalysed iodination or galactose oxidase oxidation followed by reduction with tritiated sodium borohydride. Plasma membrane glycoproteins were solubilized with the non-ionic detergent Nonidet P40 and separated by affinity chromatography on concanavalin A-Sepharose. A major water-soluble concanavalin A receptor of molecular weight greater than 160 000 was isolated by gel filtration and ion-exchange chromatography. Its amino acid and carbohydrate composition were determined. This glycoprotein is susceptible to digestion by trypsin or chymotrypsin.

Subunit structure of Achromobacter collagenase.

The highly active form of collagenase (EC 3.4.24.3) from Achromobacter iophagus (specific activity 2 microkat/mg) has a molecular weight of 70,000 and the sedimentation coefficient s20,2 = 4.4 S. It is composed of two subunits of molecular weight 35,000 and s20,w of 2.9 S. The dissociation of the dimer under different conditions resulted in the complete and irreversible loss of enzymic activity. A unique N-terminal sequence Thr-Ala-Ala-Asp-Leu-Glu-Ala-Leu-Val- indicates that the two subunits are identical, at least in the N-terminal part of the polypeptide chain. Reduction and pyridylethylation of the subunit change neither molecular weight nor amino acid composition: therefore each subunit of molecular weight 35,000 consists of a single polypeptide chain. Another active and homogeneous form of Achromobacter collagenase (specific activity 1.64 microkat/mg) gives a value for the apparent molecular weight of 80,000 on sodium dodecyl sulphate-polyacrylamide electrophoresis. It is also a dimer in which each of the two subunits of molecular weight 35,000 binds non-covalently a peptide of molecular weight 5000. The dissociation of this form of collagenase is also accompanied by irreversible loss of enzymic activity. The amino acid composition of the subunits which were isolated from both 70,000 and 80,000 collagenases is the same. The role of dimer-monometer equilibrium in the biological function of collagenase is discussed.

Chemical characterization of the homogeneous collagenase from Clostridium histolyticum.

Pure collagenase (clostridiopeptidase A, EC 3.4.24.3) having a molecular weight of 70 000 was obtained from the culture medium of Clostridium histolyticym by a combination of ultrafiltrations, molecular sieve, affinity and hydrophobic chromatography. The value of its specific activity is the highest of those described previously but 6-times lower than that of the collagenase from Achromobacter iophagus (EC 3.4.24.8). Its amino acid composition differs from previous data, namely by the presence of cysteine, methionine, tryptophan and O-phosphoserine residues. In contrast to Achromobacter collagenase it does not dissociate in subunits during the deactivation by EDTA or LiCl/glycine buffer at pH 10.5. Existence of multiple forms of Clostridium collagenase previously described is discussed as being due to autolysis of a single molecular species or to a different degree of phosphorylation.

Circular dichroism comparative studies of two bacterial collagenases and thermolysin.

The recently isolated and purified collagenase produced by Achromobacter iophagus, the collagenase from Clostridium histolyticum, and thermolysin, three enzymes having common properties, were studied by circular dichroism. From the spectra of the aqueous solutions obtained in the peptide region, the fraction of alpha helix, beta sheet and aperiodic segments in the three proteins could be estimated. Good similarity was found between Achromobacter collagenase and thermolysin, which both contain a high fraction of alpha helix. Side-chain contributions were analyzed in the aromatic region of thespectra: effects of pH and of organic solvents were observed, showing the strong influence of surroundings on the stabilization of the proteins.

Hypodermin A, a trypsin-like neutral proteinase from the insect Hypoderma lineatum.

Hypodermin A, a serine proteinase from the larva Hypoderma lineatum, with a molecular weight of 27 000 was obtained in pure form by ion-exchange chromatography. It is inhibited by diisopropyl phosphofluorate, a serine proteinase inhibitor, but not by metallo or cysteine enzyme inhibitors such as EDTA or thiol reagents. In the same way, it is fully inactivated by trypsin inhibitors, but not by specific chymotrypsin inhibitors. Its specificity, limited to carboxyl side of arginine residue in B-chain of insulin, is more complicated on other polypeptide substrates. Sequence analysis suggests structural homology with H. lineatum collagenase as well as with other members of the trypsin family.

A comparison of surface proteins in embryonal carcinoma cells and their differentiated derivatives.

Surface proteins from five cell lines (three embryonal carcinoma cell lines (F9, PCC4 and PCC3), teratocarcinoma-derived endodermal cells (PYS) and fibroblasts (line 3/A/1-D-3 differentiated from PCC3) were compared by two-dimensional polyacrylamide gel electrophoresis after selective iodination with 125I in the presence of lactoperoxidase. The labeled proteins were solubilized either in Nonidet P40/urea/ampholyte/mercaptoethanol solution or in Nonidet P40 only. In total, about thirty major 125I-labeled surface proteins were identified by their isoelectric point and molecular weight. 14 proteins are present in all five cell types, although their quantity or accessibility for labeling differs between differentiated and undifferentiated cells. Three proteins (200, 160 and 150 kilodaltons) are present in undifferentiated cells only. Two of them (160 and 150 kilodaltons) were solubilized by Nonidet P40/urea/ampholyte/mercaptoethanol, but not by Nonidet P40. One protein (50 kilodaltons) was found in nullipotent F9 cells only. About 14--15 proteins (including fibronectin) were released by Nonidet P40/urea/ampholyte/mercaptoethanol but not by Nonidet P40. They are presumably bound to submembrane or cytoskeleton structures by non-covalent bonds.

Cell-surface collagen-binding protein in the procaryote Achromobacter iophagus.

Collagen and its high-molecular-weight fragments specifically induce an extracellular collagenase (EC 3.4.24.8) in the Gram-negative Achromobacter iophagus. During the induction process the inducer is concentrated on the bacterial outer membrane. Two-dimensional electrophoresis of 125I-labelled outer membrane proteins has shown that, in particular, the amount of one protein which is already present on the surface of non-induced bacteria increases quantitatively when the inducer is added. After 125I-labelling of the cell membrane and its solubilization, the same protein is retained selectively on a gelatin-Sepharose column. It has isoelectric point of 4.9-5.1 and molecular weight of 40000. This molecular weight is close to that of the 35000 of the collagenase subunit. However, their non-identity was proved in three independent ways: upon two-dimensional electrophoresis, only those proteins in the range corresponding to the collagenase dimer (Mr 70000-80000) react with fluorescent anticollagenase antibody system, whereas the spot of the collagen-binding protein (mr 40000) is negative; the solubilized collagen-binding protein is not retained by anticollagenase-Sepharose affinity chromatography; in vivo, it is not protected by anti-collagenase antibodies against lactoperoxidase iodination. A hypothesis for the possible role of the collagen-binding protein in the induction of collagenase is proposed.

Chemical modifications of Achromobacter collagenase and their influence on the enzymic activity.

A study of the influence of chemical modifications on the activity of Achromobacter iophagus collagenase (EC 3.4.24.8) has led to the following conclusions: a modification of 4 out of 80 COOH groups with carbodiimide led to 90% loss of enzymic activity. A 70% inactivation was found after modification of two tyrosines out of 30 with tetranitromethane. The modification of four to six tryptophans out of 16 with 2-hydroxy-5-nitrobenzyl bromide decreased enzyme activity to 36%. This inactivation is accelerated in the presence of collagen. An increase of reagent/enzyme molar ratio led to a modification of 16 tryptophan residues and denaturation of Acahromobacter collagenase. A modification of two arginines out of 18 with 1,2-cyclohexanedione and eight NH2 groups out of 24 with 2,3-dimethyl maleic anhydride does not change the collagenolytic activity. All NH2 groups become available for 2,3-dimethyl maleic anhydride after dissociation of the dimer. A possible analogy of hydrolytic site of collagenase with that of two other known bacterial metalloproteinases (thermolysin and Bacillus subtilis neutral proteinase (EC 3.4.24.4)) is discussed.

Evidence for an active-center cysteine in the SH-proteinase alpha-clostripain through use of N-tosyl-L-lysine chloromethyl ketone.

The rapid reaction of alpha-clostripain with tosyl-L-lysine chloromethyl ketone results in a complete loss of activity and in the disappearance of one titratable SH group whereas the number of histidine residues is not affected. Tosyl-L-phenylalanine chloromethyl ketone and phenylmethylsulfonyl fluoride have no effect on the catalytic activity. From the molar ratio and under the assumption of 1:1 molar interaction, the fully active enzyme has a specific activity of 650-700 units/mg [twice the value proposed by Porter et al. (J. Biol. Chem. 246 (1971) 7675-7682)]. Partial oxidation makes it experimentally impossible to attain this maximal value.

Collagenase in mineralized tissues of human teeth.

A collagenase cleaving native type I [14C]collagen but inactive against the synthetic substrate Pz-Pro-Leu-Gly-Pro-D-Arg was extracted from mineralized human dental tissue. The enzyme specifically degrades native collagen into characteristic products (3/4) and (1/4). Its apparent molecular mass of 68 kDa is relatively high in comparison with collagenases from other oral tissues. The enzyme is a metalloproteinase inhibited by low concentrations of the chelating agents EDTA, 1, 10-phenanthroline, alpha alpha'-dipyridyl, and not affected by diisopropylfluorophosphate, soybean trypsin inhibitor, and p-chloromercuribenzoate. It is stable to lyophilization and can be stored at-20 degrees C for at least 6 months.

Factor V enhances the cofactor function of protein S in the APC-mediated inactivation of factor VIII: influence of the factor VR506Q mutation.

Factor V and protein S are cofactors of activated protein C (APC) which accelerate APC-mediated factor VIII inactivation. The effects of factor V and protein S were quantitated in a reaction system in which plasma factor VIII was inactivated by APC and the loss of factor VIII activity was monitored in a factor X-activating system in which a chromogenic substrate was used to probe factor Xa formation. Factor V increased the rate of APC-mediated factor VIII inactivation in a dose-dependent manner in representative plasma samples with protein S or factor V deficiency, abnormal factor V (heterozygous or homozygous for factor VR506Q), or a combination of heterozygous protein S deficiency and heterozygous factor VR506Q. This effect was much less pronounced in the plasma samples with a decreased protein S level, but the impaired response in these plasmas was corrected by addition of protein S, indicating that both factor V and protein S are required for optimal inactivation of factor VIII by APC. The effects of factor V and protein S were also studied in a reaction system with purified proteins. APC-catalysed factor VIII inactivation was enhanced 3.7-fold in the presence of 1.1 nM factor V and 1.5-fold in the presence of 2.4 nM protein S. When both 1.1 nM factor V and 2.4 nM protein were present the rate enhancement was 11-fold. Factor V is a more potent cofactor than protein S, as can be concluded from the fact that 0.04 nM factor V gave the same stimulation as 2.4 nM protein S. Protein S lost its cofactor function after complexation with C4b binding protein, which indicates that it is free protein S that acts as a cofactor. To investigate the effect of the R506Q mutation in factor V on APC-mediated factor VIII inactivation, factor V was purified from the plasma of patients homozygous for factor VR506Q. In the absence of protein S, factor VR506Q did not enhance factor VIII inactivation by APC, but in the presence of 2.4 nM protein S a slight enhancement was observed. The APC cofactor activity of factor V was lost when factor V was activated with thrombin or with the factor V activator from Russell's viper venom. These data indicate that optimal inactivation of factor VIII by APC requires the presence of an intact factor V molecule and free protein S.

Hypertension in a population sample of female Punjabi Indians in Southall.

A population-based survey of female Punjabi Indians aged 11 and over now living in Southall, a district in west London, showed a steady and significant increase in blood pressure with increasing age. The crude population prevalence of hypertension, defined according to the criteria of the World Health Organisation, was 16%; for women over the age of 40 it was 62%. About two-thirds of those in the hypertensive range did not know of their high blood pressure. Among those who did know, up to 75% were receiving medical treatment for the condition.