Maturation of the Human Cerebral Cortex During Adolescence: Myelin or Dendritic Arbor?

Previous in vivo studies revealed robust age-related variations in structural properties of the human cerebral cortex during adolescence. Neurobiology underlying these maturational phenomena is largely unknown. Here we employ a virtual-histology approach to gain insights into processes associated with inter-regional variations in cortical microstructure and its maturation, as indexed by magnetization transfer ratio (MTR). Inter-regional variations in MTR correlate with inter-regional variations in expression of genes specific to pyramidal cells (CA1) and ependymal cells; enrichment analyses indicate involvement of these genes in dendritic growth. On the other hand, inter-regional variations in the change of MTR during adolescence correlate with inter-regional profiles of oligodendrocyte-specific gene expression. Complemented by a quantitative hypothetical model of the contribution of surfaces associated with dendritic arbor (1631 m2) and myelin (48 m2), these findings suggest that MTR signals are driven mainly by macromolecules associated with dendritic arbor while maturational changes in the MTR signal are associated with myelination.

The Arf6 activator Efa6/PSD3 confers regional specificity and modulates ethanol consumption in Drosophila and humans.

Ubiquitously expressed genes have been implicated in a variety of specific behaviors, including responses to ethanol. However, the mechanisms that confer this behavioral specificity have remained elusive. Previously, we showed that the ubiquitously expressed small GTPase Arf6 is required for normal ethanol-induced sedation in adult Drosophila. Here, we show that this behavioral response also requires Efa6, one of (at least) three Drosophila Arf6 guanine exchange factors. Ethanol-naive Arf6 and Efa6 mutants were sensitive to ethanol-induced sedation and lacked rapid tolerance upon re-exposure to ethanol, when compared with wild-type flies. In contrast to wild-type flies, both Arf6 and Efa6 mutants preferred alcohol-containing food without prior ethanol experience. An analysis of the human ortholog of Arf6 and orthologs of Efa6 (PSD1-4) revealed that the minor G allele of single nucleotide polymorphism (SNP) rs13265422 in PSD3, as well as a haplotype containing rs13265422, was associated with an increased frequency of drinking and binge drinking episodes in adolescents. The same haplotype was also associated with increased alcohol dependence in an independent European cohort. Unlike the ubiquitously expressed human Arf6 GTPase, PSD3 localization is restricted to the brain, particularly the prefrontal cortex (PFC). Functional magnetic resonance imaging revealed that the same PSD3 haplotype was also associated with a differential functional magnetic resonance imaging signal in the PFC during a Go/No-Go task, which engages PFC-mediated executive control. Our translational analysis, therefore, suggests that PSD3 confers regional specificity to ubiquitous Arf6 in the PFC to modulate human alcohol-drinking behaviors.

Measurement of fetal fat in utero in normal and diabetic pregnancies using magnetic resonance imaging.

OBJECTIVES: To assess the reliability of magnetic resonance imaging (MRI) to measure fetal fat volume in utero, and to study fetal growth in women with and without diabetes in view of the increased prevalence of macrosomia in the former. METHODS: We studied 26 pregnant women, 14 with pre-gestational diabetes and 12 non-diabetic controls. Fetal assessment took place at 24 weeks' gestation and again at 34 weeks by standard ultrasound biometry followed by MRI at 1.5 T. Fetal fat volume was determined from T1-weighted water-suppressed images using a semi-automated approach based on pixel intensity and taking into account partial volume effects. Fetal volume was also determined from the MRI images. Fetal weight was calculated using published fat and lean tissue densities. RESULTS: There was little fetal fat at 24 weeks' gestation, but at 34 weeks the fetal fat content was considerably higher in the women with diabetes, with a mean fat content of 1090 ± 417 cm(3) compared with 541 ± 348 cm(3) in the controls (P = 0.006). Measurements of fetal fat volume showed low intra- and interobserver variability at 34 weeks, with intraclass correlation coefficients consistently above 0.99. Birth-weight centile correlated with fetal fat volume (R(2) = 0.496, P < 0.001), percentage of fetal fat (R(2) = 0.362, P = 0.008) and calculated fetal weight (R(2) = 0.492, P < 0.001) at 34 weeks. CONCLUSIONS: MRI appears to be a promising tool for the determination of fetal fat, body composition and weight in utero during the third trimester of pregnancy.

Measuring venous blood volume changes during activation using hyperoxia.

This study describes a novel method for measuring relative changes in venous cerebral blood volume (CBVv) using hyperoxia as a contrast agent. This method exploits the extravascular BOLD effect and its dependency on both task-related activation induced changes in venous blood oxygenation and changes due to breathing an oxygen enriched gas mixture. Changes in CBVv on activation can be estimated by comparing the change in transverse relaxation rate, R2*, due to hyperoxia in both baseline and activation states. Furthermore these measurements can be converted into a measure of the percentage change in CBVv. Experiments were performed to measure changes in a CBVv-weighted signal in response to a simple motor task. Both positive and negative changes in CBVv-weighted signal were detected in the positively activated BOLD region.

Magnetization transfer phenomenon in the human brain at 7 T.

Magnetization transfer is an important source of contrast in magnetic resonance imaging which is sensitive to the concentration of macromolecules and other solutes present in the tissue. Magnetization transfer effects can be visualized in magnetization transfer ratio images or quantified via the z-spectrum. This paper presents methods of measuring the z-spectrum and of producing high-resolution MTR images and maps of z-spectrum asymmetry in vivo at 7 T, within SAR limits. It also uses a 3-compartment model to measure chemical exchange and magnetization transfer parameters from the z-spectrum data. The peak in the z-spectrum associated with chemical exchange between amide and water protons (amide proton transfer, APT, effects) is much more apparent at 7 T than at 3 T. Furthermore at 7 T quantitative APT results varied between the corpus callosum and other white matter structures, suggesting that quantitative APT imaging could be used as a method of measuring myelination. The results also suggest that chemical exchange is not responsible for the phase shift observed in susceptibility weighted images between grey matter and white matter.

An exploratory study of sunitinib plus paclitaxel as first-line treatment for patients with advanced breast cancer.

BACKGROUND: Sunitinib has shown single-agent activity in patients with previously treated metastatic breast cancer (MBC). We investigated the safety of the combination of sunitinib and paclitaxel in an exploratory study of patients with locally advanced or MBC. METHODS: Patients received oral sunitinib 25 mg/day (with escalation to 37.5 mg/day as tolerated) on a continuous daily dosing schedule and paclitaxel 90 mg/m(2) on days 1, 8, and 15 of each 28-day cycle. Study endpoints included safety (primary endpoint), pharmacokinetics, and antitumor activity. RESULTS: Twenty-two patients were enrolled. The most frequent adverse events (AEs) were fatigue/asthenia (77%), dysgeusia (68%), and diarrhea (64%). Grade 3 AEs included neutropenia (43%), fatigue/asthenia (27%), neuropathy (18%), and diarrhea (14%). No drug-drug interaction was observed on the basis of pharmacokinetic analysis. Of 18 patients with measurable disease at baseline, 7 (38.9%) achieved objective responses (including 2 complete and 5 partial responses). Clinical responses were observed in three of nine patients with triple-negative receptor status (estrogen receptor negative, progesterone receptor negative, and human epidermal growth factor receptor-2 negative). CONCLUSIONS: These data indicate that sunitinib and paclitaxel in combination are well tolerated in patients with locally advanced or MBC. No drug-drug interaction was detected and there was preliminary evidence of antitumor activity.

Syphilitic aneurysm.

Syphilis was once the most common cause of aortic aneurysm. For the last 60 years syphilis has been well controlled in the UK population. However, we present the recent case of a 52-year-old female black South African immigrant who was found to have a syphilitic aneurysm.

Perturbation of the BOLD response by a contrast agent and interpretation through a modified balloon model.

This study used an infusion of a paramagnetic contrast agent to perturb intravascular blood susceptibility and investigate its effect on the BOLD hemodynamic response. A three compartment BOLD signal model combined with a modified balloon model was developed to interpret the MR signal. This model incorporated arterial blood volume in order to simulate signal changes resulting from the contrast agent. The BOLD signal model was fitted to the experimental data to test the hypothesis that arterial blood volume changes during activation. It was found that allowing arterial blood volume to change, rather than assuming this change is negligible as often assumed in the literature, provides a better fit to the experimental data, particularly during the BOLD overshoot. The post-stimulus undershoot was fitted well, regardless of whether the arterial blood volume was allowed to change, by assuming that this feature is due to delayed venous compliance. However the resultant elevation in post-stimulus blood volume decays with an extremely long time constant, taking more than 55 s to recover to baseline following a 4.8 s stimulus. The post-stimulus signal changes measured here could alternatively be described by a post-stimulus elevation in metabolism. An alternative model of oxygen extraction, in place of the Oxygen Limitation model, would be required to test this hypothesis.

Implementation of quantitative perfusion imaging using pulsed arterial spin labeling at ultra-high field.

This study compares the implementation of the STAR and FAIR pulsed arterial spin labeling (PASL) schemes to form quantitative perfusion maps at ultra-high field, 7 Tesla (T), and high field, 3 T. Phantom experiments were performed to compare the inversion efficiency and profile of the labeling pulses at 7 T and 3 T and to optimize in-plane saturation techniques. The perfusion weighted (PW) signal was measured at a range of postlabeling delay times and quantitative perfusion maps were calculated on a voxel-by-voxel basis. An increase in PW signal was found with field strength, and together with the increased signal-to-noise ratio, this led to improved image signal-to-noise and quality of fit of perfusion maps at 7 T.

Field strength dependence of R1 and R2* relaxivities of human whole blood to ProHance, Vasovist, and deoxyhemoglobin.

This study has measured the longitudinal and transverse (T2* relaxivity curves for ProHance (Gadoteridol), Vasovist (Gadofosveset) and deoxyhemoglobin at 1.5, 3.0, and 7.0 Tesla. The plots of R(1) versus both contrast agent and deoxyhemoglobin concentration were linear. The plots of R2* versus deoxyhemoglobin concentration showed a quadratic dependence. R2* versus contrast agent concentration showed a parabolic dependence with a minimum occurring at contrast agent concentrations of approximately 1.5 mM, corresponding to an accessible concentration in vivo. Monte Carlo simulations were performed to support the hypothesis that the minimum results from the susceptibility of the red blood cells being matched to the susceptibility of the plasma. Relaxivity values (s(-1)mM(-1)) for R2* and R1 for all agents and all three field strengths are given.

Temperature increase in the fetus due to radio frequency exposure during magnetic resonance scanning.

This letter uses data from the literature to estimate the temperature rise in the fetus due to RF deposition within normal SAR limits for the pregnant woman. The results suggest that caution should be exercised when performing fetal MRI at high SAR levels until further data are available. It makes several recommendations related to fetal MRI and fetal SAR modelling.

Cortical differences in diverticular disease and correlation with symptom reports.

BACKGROUND: Recent studies have shown that the brain of patients with gastrointestinal disease differ both structurally and functionally from that of controls. Highly somatizing diverticular disease (HSDD) patients were also shown to differ from low somatizing (LSDD) patients functionally. This study aimed to investigate how they differed structurally. METHODS: Four diseases subgroups were studied in a cross-sectional design: 20 patients with asymptomatic diverticular disease (ADD), 18 LSDD, 16 HSDD, and 18 with irritable bowel syndrome. We divided DD patients into LSDD and HSDD using a cutoff of 6 on the Patient Health Questionnaire 12 Somatic Symptom (PHQ12-SS) scale. All patients underwent a 1-mm isotropic structural brain MRI scan and were assessed for somatization, hospital anxiety, depression, and pain catastrophizing. Whole brain volumetry, cortical thickness analysis and voxel-based morphometry were carried out using Freesurfer and SPM. KEY RESULTS: We observed decreases in gray matter density in the left and right dorsolateral prefrontal cortex (dlPFC), and in the mid-cingulate and motor cortex, and increases in the left (19, 20) and right (19, 38) Brodmann Areas. The average cortical thickness differed overall across groups (P = .002) and regionally: HSDD > ADD in the posterior cingulate cortex (P = .03), HSDD > LSDD in the dlPFC (P = .03) and in the ventrolateral PFC (P < .001). The thickness of the anterior cingulate cortex and of the mid-prefrontal cortex were also found to correlate with Pain Catastrophizing (Spearman's ρ = 0.24, P = .043 uncorrected and Spearman's ρ = 0.25, P = .03 uncorrected). CONCLUSION & INFERENCES: This is the first study of structural gray matter abnormalities in diverticular disease patients. The data show brain differences in the pain network.

MRI assessment of the postprandial gastrointestinal motility and peptide response in healthy humans.

BACKGROUND: Feeding triggers inter-related gastrointestinal (GI) motor, peptide and appetite responses. These are rarely studied together due to methodological limitations. Recent MRI advances allow pan-intestinal, non-invasive assessment of motility in the undisturbed gut. This study aimed to develop a methodology to assess pan-intestinal motility and transit in a single session using MRI and compare imaging findings to GI peptide responses to a test meal and symptoms in a healthy volunteer cohort. METHODS: Fifteen healthy volunteers (29.3±2.7 years and BMI 20.1±1.2 kg m-2 ) underwent baseline and postprandial MRI scans, symptom questionnaires, and blood sampling (for subsequent GI peptide analysis, Glucagon-like peptide-1 [GLP-1], Polypeptide YY [PYY], Cholecystokinin [CCK]) at intervals for 270 minutes following a 400 g soup meal (204 kcal, Heinz, UK). Gastric volume, gall bladder volume, small bowel water content, small bowel motility, and whole gut transit were measured from the MRI scans. KEY RESULTS: (mean±SEM) Small bowel motility index increased from fasting 39±3 arbitrary units (a.u.) to a maximum of 87±7 a.u. immediately after feeding. PYY increased from fasting 98±10 pg mL-1 to 149±14 pg mL-1 at 30 minutes and GLP-1 from fasting 15±3 µg mL-1 to 22±4 µg mL-1 . CCK increased from fasting 0.40±0.06 pmol mL-1 to 0.94±0.1 pmol mL-1 . Gastric volumes declined with a T1/2 of 46±5 minute and the gallbladder contracted from a fasting volume of 19±2 mL-1 to 12±2 mL-1 . Small bowel water content increased from 39±2 mL-1 to 51±2 mL-1 postprandial. Fullness VAS score increased from 9±5 mm to 41±6 mm at 30 minutes postprandial. CONCLUSIONS AND INFERENCES: The test meal challenge was effective in inducing a change in MRI motility end-points which will improve understanding of the pathophysiological postprandial GI response.

Theoretical optimization of multi-echo fMRI data acquisition.

Simulations are used to optimize multi-echo fMRI data acquisition for detection of BOLD signal changes in this study. Optimal sequence design (echo times and sampling period (receiver bandwidth)) and the variation in sensitivity between tissues with different baseline T*(2) are investigated, taking into account the effects of physiological noise and non-exponential signal decay. In the case of a single echo, for normally distributed, uncorrelated noise, the results indicate that the sampling period should be made as long as possible (so as to produce an acceptable level of image distortion), up to a maximum sampling period of 3T*(2), (i.e. optimum TE = 1.5T*(2)). Combining the signal from multiple echoes using weighted summation improves the contrast-to-noise ratio (CNR), at a reduced optimum echo interval. If the BOLD effect causes a constant change in relaxation rate, DeltaR*(2), independent of the tissue R*(2), then a multi-echo acquisition causes considerable variation in sensitivity to BOLD signal changes with tissue T*(2), so that if the sequence is optimized for a target tissue T*(2) it will be more sensitive to BOLD signal changes in tissues with shorter T*(2) values. Fitting for DeltaR*(2) reduces the CNR, and when using this approach, the shortest echo time interval should be used, down to a limit of about 0.3T*(2), and as many echoes as possible within the constraints of TR or hardware limitations should be collected. It is also shown that the optimal sequence will remain optimum or close to optimum irrespective of whether there are physiological noise contributions.

Non-invasive quantification of small bowel water content by MRI: a validation study.

Substantial water fluxes across the small intestine occur during digestion of food, but so far measuring these has required invasive intubation techniques. This paper describes a non-invasive magnetic resonance imaging (MRI) technique for measuring small bowel water content which has been validated using naso-duodenal infusion. Eighteen healthy volunteers were intubated, with the tube position being verified by MRI. After a baseline MRI scan, each volunteer had eight 40 ml boluses of a non-absorbable mannitol and saline solution infused into their proximal small bowel with an MRI scan being acquired after each bolus. The MRI sequence used was an adapted magnetic resonance cholangiopancreatography sequence. The image data were thresholded to allow for intra- and inter-subject signal variations. The MRI measured volumes were then compared to the known infused volumes. This MRI technique gave excellent images of the small bowel, which closely resemble those obtained using conventional radiology with barium contrast. The mean difference between the measured MRI volumes and infused volumes was 2% with a standard deviation of 10%. The maximum 95% limits of agreement between observers were -15% to +17% while measurements by the same operator on separate occasions differed by only 4%. This new technique can now be applied to study alterations in small bowel fluid absorption and secretion due to gastrointestinal disease or drug intervention.

Assessment of motion of colonic contents in the human colon using MRI tagging.

BACKGROUND: We have previously reported a non-invasive, semi-automated technique to assess motility of the wall of the ascending colon (AC) using Magnetic Resonance Imaging. This study investigated the feasibility of using a tagged MRI technique to visualize and assess the degree of flow within the human ascending colon in healthy subjects and those suffering from constipation. METHODS: An open-labeled study of 11 subjects with constipation and 11 subjects without bowel disorders was performed. MRI scans were acquired fasted, then 60 and 120 minutes after ingestion of a 500 mL macrogol preparation. The amount of free fluid in the small and large bowel was assessed using a heavily T2-weighted MRI sequence. The internal movement of the contents of the AC was visualized using a cine tagged MRI sequence and assessed by a novel analysis technique. Comparisons were made between fasting and postprandial scans within individuals, and between the constipation and control groups. KEY RESULTS: Macrogol significantly increased the mobile, MR visible water content of the ascending colon at 60 minutes postingestion compared to fasted data (controls P=.001, constipated group P=.0039). The contents of the AC showed increased motion in healthy subjects but not in the constipated group with significant differences between groups at 60 minutes (P<.002) and 120 minutes (P<.003). CONCLUSIONS AND INFERENCES: This study successfully demonstrated the use of a novel MRI tagging technique to visualize and assess the motion of ascending colon contents following a 500 mL macrogol challenge. Significant differences were demonstrated between healthy and constipated subjects.

Present and future magnetic resonance sources of exposure to static fields.

This paper considers the exposure of humans to static magnetic fields due to magnetic resonance imaging (MRI) procedures. It briefly introduces the types of magnetic fields associated with MRI. It then discusses trends in the number of people exposed to MRI, the field strength of the magnets used in MRI, and the types of applications of MRI. It also considers the types of staff who are exposed to magnetic fields due to MRI, and the alternative techniques that would be used in the absence of MRI.

Investigating the effects of an oral fructose challenge on hepatic ATP reserves in healthy volunteers: A (31)P MRS study.

BACKGROUND: Impaired homeostasis of hepatic ATP has been associated with NAFLD. An intravenous fructose infusion has been shown to be an effective challenge to monitor the depletion and subsequent recovery of hepatic ATP reserves using (31)P MRS. AIMS: The purpose of this study was to evaluate the effects of an oral rather than intravenous fructose challenge on hepatic ATP reserves in healthy subjects. METHODS: Self-reported healthy males were recruited. Following an overnight fast, baseline liver glycogen and lipid levels were measured using Magnetic Resonance Spectroscopy (MRS). Immediately after consuming a 500 ml 75 g fructose drink (1275 kJ) subjects were scanned continuously for 90 min to acquire dynamic (31)P MRS measurements of liver ATP reserves. RESULTS: A significant effect on ATP reserves was observed across the time course (P < 0.05). Mean ATP levels reached a minimum at 50 min which was markedly lower than baseline (80 ± 17% baseline, P < 0.05). Subsequently, mean values tended to rise but did not reach statistical significance above minimum. The time to minimum ATP levels across subjects was negatively correlated with BMI (R(2) = 0.74, P < 0.005). Rates of ATP recovery were not significantly correlated with BMI or liver fat levels, but were negatively correlated with baseline glycogen levels (R(2) = 0.7, P < 0.05). CONCLUSIONS: Depletion of ATP reserves can be measured non-invasively following an oral fructose challenge using (31)P MRS. BMI is the best predictor of postprandial ATP homeostasis following fructose consumption.

Colon wall motility: comparison of novel quantitative semi-automatic measurements using cine MRI.

BACKGROUND: Recently, cine magnetic resonance imaging (MRI) has shown promise for visualizing movement of the colonic wall, although assessment of data has been subjective and observer dependent. This study aimed to develop an objective and semi-automatic imaging metric of ascending colonic wall movement, using image registration techniques. METHODS: Cine balanced turbo field echo MRI images of ascending colonic motility were acquired over 2 min from 23 healthy volunteers (HVs) at baseline and following two different macrogol stimulus drinks (11 HVs drank 1 L and 12 HVs drank 2 L). Motility metrics derived from large scale geometric and small scale pixel movement parameters following image registration were developed using the post ingestion data and compared to observer grading of wall motion. Inter and intra-observer variability in the highest correlating metric was assessed using Bland-Altman analysis calculated from two separate observations on a subset of data. KEY RESULTS: All the metrics tested showed significant correlation with the observer rating scores. Line analysis (LA) produced the highest correlation coefficient of 0.74 (95% CI: 0.55-0.86), p < 0.001 (Spearman Rho). Bland-Altman analysis of the inter- and intra-observer variability for the LA metric, showed almost zero bias and small limits of agreement between observations (-0.039 to 0.052 intra-observer and -0.051 to 0.054 inter-observer, range of measurement 0-0.353). CONCLUSIONS & INFERENCES: The LA index of colonic motility derived from cine MRI registered data provides a quick, accurate and non-invasive method to detect wall motion within the ascending colon following a colonic stimulus in the form of a macrogol drink.

Additive effects of gastric volumes and macronutrient composition on the sensation of postprandial fullness in humans.

BACKGROUND/OBJECTIVES: Intake of food or fluid distends the stomach and triggers mechanoreceptors and vagal afferents. Wall stretch and tension produces a feeling of fullness. Duodenal infusion studies assessing gastric sensitivity by barostat have shown that the products of fat digestion have a greater effect on the sensation of fullness and also dyspeptic symptoms than carbohydrates. We tested here the hypothesis that fat and carbohydrate have different effects on gastric sensation under physiological conditions using non-invasive magnetic resonance imaging (MRI) to measure gastric volumes. SUBJECTS/METHODS: Thirteen healthy subjects received a rice pudding test meal with added fat or added carbohydrate on two separate occasions and underwent serial postprandial MRI scans for 4.5 h. Fullness was assessed on a 100-mm visual analogue scale. RESULTS: Gastric half emptying time was significantly slower for the high-carbohydrate meal than for the high-fat meal, P=0.0327. Fullness significantly correlated with gastric volumes for both meals; however, the change from baseline in fullness scores was higher for the high-fat meal for any given change in stomach volume (P=0.0147), despite the lower energy content and faster gastric emptying of the high-fat meal. CONCLUSIONS: Total gastric volume correlates positively and linearly with postprandial fullness and ingestion of a high-fat meal increases this sensation compared with high-carbohydrate meal. These findings can be of clinical interest in patients presenting with postprandial dyspepsia whereby manipulating gastric sensitivity by dietary intervention may help to control digestive sensations.