Clinical Evaluation of Scout Accelerated Motion Estimation and Reduction Technique for 3D MR Imaging in the Inpatient and Emergency Department Settings.

BACKGROUND AND PURPOSE: A scout accelerated motion estimation and reduction (SAMER) framework has been developed for efficient retrospective motion correction. The goal of this study was to perform an initial evaluation of SAMER in a series of clinical brain MR imaging examinations. MATERIALS AND METHODS: Ninety-seven patients who underwent MR imaging in the inpatient and emergency department settings were included in the study. SAMER motion correction was retrospectively applied to an accelerated T1-weighted MPRAGE sequence that was included in brain MR imaging examinations performed with and without contrast. Two blinded neuroradiologists graded images with and without SAMER motion correction on a 5-tier motion severity scale (none = 1, minimal = 2, mild = 3, moderate = 4, severe = 5). RESULTS: The median SAMER reconstruction time was 1 minute 47 seconds. SAMER motion correction significantly improved overall motion grades across all examinations (P < .005). Motion artifacts were reduced in 28% of cases, unchanged in 64% of cases, and increased in 8% of cases. SAMER improved motion grades in 100% of moderate motion cases and 75% of severe motion cases. Sixty-nine percent of nondiagnostic motion cases (grades 4 and 5) were considered diagnostic after SAMER motion correction. For cases with minimal or no motion, SAMER had negligible impact on the overall motion grade. For cases with mild, moderate, and severe motion, SAMER improved the motion grade by an average of 0.3 (SD, 0.5), 1.1 (SD, 0.3), and 1.1 (SD, 0.8) grades, respectively. CONCLUSIONS: SAMER improved the diagnostic image quality of clinical brain MR imaging examinations with motion artifacts. The improvement was most pronounced for cases with moderate or severe motion.

Evaluation of Ultrafast Wave-Controlled Aliasing in Parallel Imaging 3D-FLAIR in the Visualization and Volumetric Estimation of Cerebral White Matter Lesions.

BACKGROUND AND PURPOSE: Our aim was to evaluate an ultrafast 3D-FLAIR sequence using Wave-controlled aliasing in parallel imaging encoding (Wave-FLAIR) compared with standard 3D-FLAIR in the visualization and volumetric estimation of cerebral white matter lesions in a clinical setting. MATERIALS AND METHODS: Forty-two consecutive patients underwent 3T brain MR imaging, including standard 3D-FLAIR (acceleration factor = 2, scan time = 7 minutes 50 seconds) and resolution-matched ultrafast Wave-FLAIR sequences (acceleration factor = 6, scan time = 2 minutes 45 seconds for the 20-channel coil; acceleration factor = 9, scan time = 1 minute 50 seconds for the 32-channel coil) as part of clinical evaluation for demyelinating disease. Automated segmentation of cerebral white matter lesions was performed using the Lesion Segmentation Tool in SPM. Student t tests, intraclass correlation coefficients, relative lesion volume difference, and Dice similarity coefficients were used to compare volumetric measurements among sequences. Two blinded neuroradiologists evaluated the visualization of white matter lesions, artifacts, and overall diagnostic quality using a predefined 5-point scale. RESULTS: Standard and Wave-FLAIR sequences showed excellent agreement of lesion volumes with an intraclass correlation coefficient of 0.99 and mean Dice similarity coefficient of 0.97 (SD, 0.05) (range, 0.84-0.99). Wave-FLAIR was noninferior to standard FLAIR for visualization of lesions and motion. The diagnostic quality for Wave-FLAIR was slightly greater than for standard FLAIR for infratentorial lesions (P < .001), and there were fewer pulsation artifacts on Wave-FLAIR compared with standard FLAIR (P < .001). CONCLUSIONS: Ultrafast Wave-FLAIR provides superior visualization of infratentorial lesions while preserving overall diagnostic quality and yields white matter lesion volumes comparable with those estimated using standard FLAIR. The availability of ultrafast Wave-FLAIR may facilitate the greater use of 3D-FLAIR sequences in the evaluation of patients with suspected demyelinating disease.

Severity of Chest Imaging is Correlated with Risk of Acute Neuroimaging Findings among Patients with COVID-19.

BACKGROUND AND PURPOSE: Severe respiratory distress in patients with COVID-19 has been associated with higher rate of neurologic manifestations. Our aim was to investigate whether the severity of chest imaging findings among patients with coronavirus disease 2019 (COVID-19) correlates with the risk of acute neuroimaging findings. MATERIALS AND METHODS: This retrospective study included all patients with COVID-19 who received care at our hospital between March 3, 2020, and May 6, 2020, and underwent chest imaging within 10 days of neuroimaging. Chest radiographs were assessed using a previously validated automated neural network algorithm for COVID-19 (Pulmonary X-ray Severity score). Chest CTs were graded using a Chest CT Severity scoring system based on involvement of each lobe. Associations between chest imaging severity scores and acute neuroimaging findings were assessed using multivariable logistic regression. RESULTS: Twenty-four of 93 patients (26%) included in the study had positive acute neuroimaging findings, including intracranial hemorrhage (n = 7), infarction (n = 7), leukoencephalopathy (n = 6), or a combination of findings (n = 4). The average length of hospitalization, prevalence of intensive care unit admission, and proportion of patients requiring intubation were significantly greater in patients with acute neuroimaging findings than in patients without them (P < .05 for all). Compared with patients without acute neuroimaging findings, patients with acute neuroimaging findings had significantly higher mean Pulmonary X-ray Severity scores (5.0 [SD, 2.9] versus 9.2 [SD, 3.4], P < .001) and mean Chest CT Severity scores (9.0 [SD, 5.1] versus 12.1 [SD, 5.0], P = .041). The pulmonary x-ray severity score was a significant predictor of acute neuroimaging findings in patients with COVID-19. CONCLUSIONS: Patients with COVID-19 and acute neuroimaging findings had more severe findings on chest imaging on both radiographs and CT compared with patients with COVID-19 without acute neuroimaging findings. The severity of findings on chest radiography was a strong predictor of acute neuroimaging findings in patients with COVID-19.

Clinical, Imaging, and Lab Correlates of Severe COVID-19 Leukoencephalopathy.

BACKGROUND AND PURPOSE: Patients infected with the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) can develop a spectrum of neurological disorders, including a leukoencephalopathy of variable severity. Our aim was to characterize imaging, lab, and clinical correlates of severe coronavirus disease 2019 (COVID-19) leukoencephalopathy, which may provide insight into the SARS-CoV-2 pathophysiology. MATERIALS AND METHODS: Twenty-seven consecutive patients positive for SARS-CoV-2 who had brain MR imaging following intensive care unit admission were included. Seven (7/27, 26%) developed an unusual pattern of "leukoencephalopathy with reduced diffusivity" on diffusion-weighted MR imaging. The remaining patients did not exhibit this pattern. Clinical and laboratory indices, as well as neuroimaging findings, were compared between groups. RESULTS: The reduced-diffusivity group had a significantly higher body mass index (36 versus 28 kg/m2, P < .01). Patients with reduced diffusivity trended toward more frequent acute renal failure (7/7, 100% versus 9/20, 45%; P = .06) and lower estimated glomerular filtration rate values (49 versus 85 mL/min; P = .06) at the time of MRI. Patients with reduced diffusivity also showed lesser mean values of the lowest hemoglobin levels (8.1 versus 10.2 g/dL, P < .05) and higher serum sodium levels (147 versus 139 mmol/L, P = .04) within 24 hours before MR imaging. The reduced-diffusivity group showed a striking and highly reproducible distribution of confluent, predominantly symmetric, supratentorial, and middle cerebellar peduncular white matter lesions (P < .001). CONCLUSIONS: Our findings highlight notable correlations between severe COVID-19 leukoencephalopathy with reduced diffusivity and obesity, acute renal failure, mild hypernatremia, anemia, and an unusual brain MR imaging white matter lesion distribution pattern. Together, these observations may shed light on possible SARS-CoV-2 pathophysiologic mechanisms associated with leukoencephalopathy, including borderzone ischemic changes, electrolyte transport disturbances, and silent hypoxia in the setting of the known cytokine storm syndrome that accompanies severe COVID-19.

Evaluation of Ultrafast Wave-CAIPI MPRAGE for Visual Grading and Automated Measurement of Brain Tissue Volume.

BACKGROUND AND PURPOSE: Volumetric brain MR imaging typically has long acquisition times. We sought to evaluate an ultrafast MPRAGE sequence based on Wave-CAIPI (Wave-MPRAGE) compared with standard MPRAGE for evaluation of regional brain tissue volumes. MATERIALS AND METHODS: We performed scan-rescan experiments in 10 healthy volunteers to evaluate the intraindividual variability of the brain volumes measured using the standard and Wave-MPRAGE sequences. We then evaluated 43 consecutive patients undergoing brain MR imaging. Patients underwent 3T brain MR imaging, including a standard MPRAGE sequence (acceleration factor [R] = 2, acquisition time [TA] = 5.2 minutes) and an ultrafast Wave-MPRAGE sequence (R = 9, TA = 1.15 minutes for the 32-channel coil; R = 6, TA = 1.75 minutes for the 20-channel coil). Automated segmentation of regional brain volume was performed. Two radiologists evaluated regional brain atrophy using semiquantitative visual rating scales. RESULTS: The mean absolute symmetrized percent change in the healthy volunteers participating in the scan-rescan experiments was not statistically different in any brain region for both the standard and Wave-MPRAGE sequences. In the patients undergoing evaluation for neurodegenerative disease, the Dice coefficient of similarity between volumetric measurements obtained from standard and Wave-MPRAGE ranged from 0.86 to 0.95. Similarly, for all regions, the absolute symmetrized percent change for brain volume and cortical thickness showed <6% difference between the 2 sequences. In the semiquantitative visual comparison, the differences between the 2 radiologists' scores were not clinically or statistically significant. CONCLUSIONS: Brain volumes estimated using ultrafast Wave-MPRAGE show low intraindividual variability and are comparable with those estimated using standard MPRAGE in patients undergoing clinical evaluation for suspected neurodegenerative disease.

Validation of Highly Accelerated Wave-CAIPI SWI Compared with Conventional SWI and T2*-Weighted Gradient Recalled-Echo for Routine Clinical Brain MRI at 3T.

BACKGROUND AND PURPOSE: SWI is valuable for characterization of intracranial hemorrhage and mineralization but has long acquisition times. We compared a highly accelerated wave-controlled aliasing in parallel imaging (CAIPI) SWI sequence with 2 commonly used alternatives, standard SWI and T2*-weighted gradient recalled-echo (T2*W GRE), for routine clinical brain imaging at 3T. MATERIALS AND METHODS: A total of 246 consecutive adult patients were prospectively evaluated using a conventional SWI or T2*W GRE sequence and an optimized wave-CAIPI SWI sequence, which was 3-5 times faster than the standard sequence. Two blinded radiologists scored each sequence for the presence of hemorrhage, the number of microhemorrhages, and severity of motion artifacts. Wave-CAIPI SWI was then evaluated in head-to-head comparison with the conventional sequences for visualization of pathology, artifacts, and overall diagnostic quality. Forced-choice comparisons were used for all scores. Wave-CAIPI SWI was tested for superiority relative to T2*W GRE and for noninferiority relative to standard SWI using a 15% noninferiority margin. RESULTS: Compared with T2*W GRE, wave-CAIPI SWI detected hemorrhages in more cases (P < .001) and detected more microhemorrhages (P < .001). Wave-CAIPI SWI was superior to T2*W GRE for visualization of pathology, artifacts, and overall diagnostic quality (all P < .001). Compared with standard SWI, wave-CAIPI SWI showed no difference in the presence or number of hemorrhages identified. Wave-CAIPI SWI was noninferior to standard SWI for the visualization of pathology (P < .001), artifacts (P < .01), and overall diagnostic quality (P < .01). Motion was less severe with wave-CAIPI SWI than with standard SWI (P < .01). CONCLUSIONS: Wave-CAIPI SWI provided superior visualization of pathology and overall diagnostic quality compared with T2*W GRE and was noninferior to standard SWI with reduced scan times and reduced motion artifacts.

Cell-bound complement activation products (CB-CAPs) have high sensitivity and specificity in pediatric-onset systemic lupus erythematosus and correlate with disease activity.

OBJECTIVE: Elevated levels of cell-bound complement activation products (CB-CAPs) (C4d deposition on B lymphocytes (BC4d) and/or erythrocytes (EC4d)) are sensitive and specific in diagnosis and monitoring of adult systemic lupus erythematosus (SLE). Our objective was to evaluate the role of CB-CAPs for diagnosis and monitoring of pediatric-onset SLE (pSLE). METHODS: A prospective cohort study of 28 pSLE and 22 juvenile arthritis patients was conducted. SLE disease activity was determined using a clinical Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) that excluded serologies. Autoantibodies were measured using solid-phase immunoassays, C3 and C4 using immunoturbidimetry, and CB-CAPs using quantitative flow cytometry. Abnormal CB-CAPs were defined as EC4d or BC4d above the 99th percentile for healthy adults (>14 and > 60 net mean fluorescence intensity (MFI), respectively). Performance characteristics of CB-CAPs were assessed using area under the curve (AUC) for receiver operating characteristics. Linear mixed effect models evaluated the correlation between CB-CAPs and clinical SLEDAI over 6 months. RESULTS: BC4d yielded higher AUC (0.91 ± 0.04) than C3 (0.63 ± 0.08) and C4 (0.67 ± 0.08) ( p < 0.05). Abnormal CB-CAPs were 78% sensitive and 86% specific for diagnosis of pSLE (Youden's index = 0.64 ± 0.11). In contrast to BC4d, EC4d levels correlated with clinical SLEDAI ( p < 0.01). CONCLUSION: CB-CAPs (EC4d and BC4d) have higher sensitivity and specificity than low complement in pSLE, and may help with diagnosis of pSLE. EC4d could provide a useful biomarker for disease activity monitoring.

A Simplified Model for Intravoxel Incoherent Motion Perfusion Imaging of the Brain.

BACKGROUND AND PURPOSE: Despite a recent resurgence, intravoxel incoherent motion MRI faces practical challenges, including limited SNR and demanding acquisition and postprocessing requirements. A simplified approach using linear fitting of a subset of higher b-values has seen success in other organ systems. We sought to validate this method for evaluation of brain pathology by comparing perfusion measurements using simplified linear fitting to conventional biexponential fitting. MATERIALS AND METHODS: Forty-nine patients with gliomas and 17 with acute strokes underwent 3T MRI, including DWI with 16 b-values (range, 0-900 s/mm2). Conventional intravoxel incoherent motion was performed using nonlinear fitting of the standard biexponential equation. Simplified intravoxel incoherent motion was performed using linear fitting of the log-normalized signal curves for subsets of b-values >200 s/mm2. Comparisons between ROIs (tumors, strokes, contralateral brain) and between models (biexponential and simplified linear) were performed by using 2-way ANOVA. The root mean square error and coefficient of determination (R2) were computed for the simplified model, with biexponential fitting as the reference standard. RESULTS: Perfusion maps using simplified linear fitting were qualitatively similar to conventional biexponential fitting. The perfusion fraction was elevated in high-grade (n = 33) compared to low-grade (n = 16) gliomas and was reduced in strokes compared to the contralateral brain (P < .001 for both main effects). Decreasing the number of b-values used for linear fitting resulted in reduced accuracy (higher root mean square error and lower R2) compared with full biexponential fitting. CONCLUSIONS: Intravoxel incoherent motion perfusion imaging of common brain pathology can be performed by using simplified linear fitting, with preservation of clinically relevant perfusion information.

Vascular Dysfunction in Leukoaraiosis.

BACKGROUND AND PURPOSE: The pathogenesis of leukoaraiosis has long been debated. This work addresses a less well-studied mechanism, cerebrovascular reactivity, which could play a leading role in the pathogenesis of this disease. Our aim was to evaluate blood flow dysregulation and its relation to leukoaraiosis. MATERIALS AND METHODS: Cerebrovascular reactivity, the change in the blood oxygen level-dependent 3T MR imaging signal in response to a consistently applied step change in the arterial partial pressure of carbon dioxide, was measured in white matter hyperintensities and their contralateral spatially homologous normal-appearing white matter in 75 older subjects (age range, 50-91 years; 40 men) with leukoaraiosis. Additional quantitative evaluation of regions of leukoaraiosis was performed by using diffusion (n = 75), quantitative T2 (n = 54), and DSC perfusion MRI metrics (n = 25). RESULTS: When we compared white matter hyperintensities with contralateral normal-appearing white matter, cerebrovascular reactivity was lower by a mean of 61.2% ± 22.6%, fractional anisotropy was lower by 44.9 % ± 6.9%, and CBF was lower by 10.9% ± 11.9%. T2 was higher by 61.7% ± 13.5%, mean diffusivity was higher by 59.0% ± 11.7%, time-to-maximum was higher by 44.4% ± 30.4%, and TTP was higher by 6.8% ± 5.8% (all P < .01). Cerebral blood volume was lower in white matter hyperintensities compared with contralateral normal-appearing white matter by 10.2% ± 15.0% (P = .03). CONCLUSIONS: Not only were resting blood flow metrics abnormal in leukoaraiosis but there is also evidence of reduced cerebrovascular reactivity in these areas. Studies have shown that reduced cerebrovascular reactivity is more sensitive than resting blood flow parameters for assessing vascular insufficiency. Future work is needed to examine the sensitivity of resting-versus-dynamic blood flow measures for investigating the pathogenesis of leukoaraiosis.

Invited article: advanced drag-free concepts for future space-based interferometers: acceleration noise performance.

Future drag-free missions for space-based experiments in gravitational physics require a Gravitational Reference Sensor with extremely demanding sensing and disturbance reduction requirements. A configuration with two cubical sensors is the current baseline for the Laser Interferometer Space Antenna (LISA) and has reached a high level of maturity. Nevertheless, several promising concepts have been proposed with potential applications beyond LISA and are currently investigated at HEPL, Stanford, and EADS Astrium, Germany. The general motivation is to exploit the possibility of achieving improved disturbance reduction, and ultimately understand how low acceleration noise can be pushed with a realistic design for future mission. In this paper, we discuss disturbance reduction requirements for LISA and beyond, describe four different payload concepts, compare expected strain sensitivities in the "low-frequency" region of the frequency spectrum, dominated by acceleration noise, and ultimately discuss advantages and disadvantages of each of those concepts in achieving disturbance reduction for space-based detectors beyond LISA.

Evaluation of esophageal motor function in clinical practice.

Esophageal motor function is highly coordinated between central and enteric nervous systems and the esophageal musculature, which consists of proximal skeletal and distal smooth muscle in three functional regions, the upper and lower esophageal sphincters, and the esophageal body. While upper endoscopy is useful in evaluating for structural disorders of the esophagus, barium esophagography, radionuclide transit studies, and esophageal intraluminal impedance evaluate esophageal transit and partially assess motor function. However, esophageal manometry is the test of choice for the evaluation of esophageal motor function. In recent years, high-resolution manometry (HRM) has streamlined the process of acquisition and display of esophageal pressure data, while uncovering hitherto unrecognized esophageal physiologic mechanisms and pathophysiologic patterns. New algorithms have been devised for analysis and reporting of esophageal pressure topography from HRM. The clinical value of HRM extends to the pediatric population, and complements preoperative evaluation prior to foregut surgery. Provocative maneuvers during HRM may add to the assessment of esophageal motor function. The addition of impedance to HRM provides bolus transit data, but impact on clinical management remains unclear. Emerging techniques such as 3-D HRM and impedance planimetry show promise in the assessment of esophageal sphincter function and esophageal biomechanics.

Utilization of wireless pH monitoring technologies: a summary of the proceedings from the esophageal diagnostic working group.

Gastroesophageal reflux disease (GERD) can be difficult to diagnose - symptoms alone are often not enough, and thus, objective testing is often required. GERD is a manifestation of pathologic levels of reflux into the esophagus of acidic, nonacidic, and/or bilious gastric content. However, in our current evidence-based knowledge approach, we only have reasonable outcome data in regards to acid reflux, as this particular type of refluxate predictably causes symptoms and mucosal damage, which improves with medical or surgical therapy. While there are data suggesting that nonacid reflux may be responsible for ongoing symptoms despite acid suppression in some patients, outcome data about this issue are limited. Therefore, this working group believes that it is essential to confirm the presence of acid reflux in patients with 'refractory' GERD symptoms or extraesophageal symptoms thought to be caused by gastroesophageal reflux before an escalation of antireflux therapy is considered. If patients do not have pathologic acid reflux off antisecretory therapy, they are unlikely to have clinically significant nonacid or bile reflux. Patients who do not have pathologic acid gastroesophageal reflux parameters on ambulatory pH monitoring then: (i) could attempt to discontinue antisecretory medications like proton pump inhibitors and H2-receptor antagonists (which are expensive and which carry risks - i.e. C. diff, etc.); (ii) may undergo further evaluation for other causes of their esophageal symptoms (e.g. functional heartburn or chest pain, eosinophilic esophagitis, gastroparesis, achalasia, other esophageal motor disorders); and (iii) can be referred to an ear, nose, and throat/pulmonary/allergy physician for assessment of non-GERD causes of their extraesophageal symptoms.

Short-term electrical stimulation of the lower esophageal sphincter increases sphincter pressure in patients with gastroesophageal reflux disease.

BACKGROUND: Electrical stimulation (ES) of the lower esophageal sphincter (LES) increases resting LES pressure (LESP) in animal models. Our aims were to evaluate the safety of such stimulation in humans, and test the hypothesis that ES increases resting LESP in patients with gastroesophageal reflux disease (GERD). METHODS: A total of 10 subjects (nine female patients, mean age 52.6 years), with symptoms of GERD responsive to PPIs, low resting LES pressure, and abnormal 24-h intraesophageal pH test were enrolled. Those with hiatal hernia >2 cm and/or esophagitis >Los Angeles Grade B were excluded. Bipolar stitch electrodes were placed longitudinally in the LES during an elective laparoscopic cholecystectomy, secured by a clip and exteriorized through the abdominal wall. Following recovery, an external pulse generator delivered two types of stimulation for periods of 30 min: (i) low energy stimulation; pulse width of 200 µs, frequency of 20 Hz and current of 5-15 mA (current was increased up to 15 mA if LESP was less than 15 mmHg), and (ii) high energy stimulation; pulse width of 375 ms, frequency of 6 cpm, and current 5 mA. Resting LESP, amplitude of esophageal contractions and residual LESP in response to swallows were assessed before and after stimulation. Symptoms of chest pain, abdominal pain, and dysphagia were recorded before, during, and after stimulation and 7-days after stimulation. Continuous cardiac monitoring was performed during and after stimulation. KEY RESULTS: All patients were successfully implanted nine subjects received high frequency, low energy, and four subjects received low frequency, high energy stimulation. Both types of stimulation significantly increased resting LESP: from 8.6 mmHg (95% CI 4.1-13.1) to 16.6 mmHg (95% CI 10.8-19.2), P < 0.001 with low energy stimulation and from 9.2 mmHg (95% CI 2.0-16.3) to 16.5 mmHg (95% CI 2.7-30.1), P = 0.03 with high energy stimulation. Neither type of stimulation affected the amplitude of esophageal peristalsis or residual LESP. No subject complained of dysphagia. One subject had retrosternal discomfort with stimulation at 15 mA that was not experienced with stimulation at 13 mA. There were no adverse events or any cardiac rhythm abnormalities with either type of stimulation. CONCLUSIONS & INFERENCES: Short-term stimulation of the LES in patients with GERD significantly increases resting LESP without affecting esophageal peristalsis or LES relaxation. Electrical stimulation of the LES may offer a novel therapy for patients with GERD.

The effects of methane and hydrogen gases produced by enteric bacteria on ileal motility and colonic transit time.

BACKGROUND: Gases produced by intestinal flora may modulate intestinal motor function in healthy individuals as well as those with functional bowel disease. Methane, produced by enteric bacteria in the human gut, is associated with slowed intestinal transit and constipation. The effects of hydrogen, another main gas produced by bacterial fermentation in the gut, on small bowel and colonic motor function remains unrecognized. Therefore, we set out to investigate whether intestinal gases including methane and hydrogen could influence the small bowel motility and colonic transit. METHODS: Guinea pig ileum was placed in the peristaltic bath with tension transducers attached to measure velocity and amplitude of peristaltic contraction before and after the infusion of control, hydrogen, and methane gases. Also, changes in the intraluminal pressures were monitored before and after the gas infusions. KEY RESULTS: Methane decreased peristaltic velocity and increased contraction amplitude significantly of guinea pig ileum (P < 0.05). The AUC of intraluminal pressure was significantly increased with methane in guinea pig ileum (P < 0.05). In a second experiment, guinea pig colon was placed in the peristaltic bath to measure transit time before and after control, hydrogen, methane, and methane-hydrogen mixture gas infusions. Hydrogen shortened colonic transit time by 47% in the proximal colon, and by 10% in the distal colon, when compared with baselines (P < 0.05). CONCLUSIONS & INFERENCES: Methane delayed ileal peristaltic conduction velocity by augmenting contractility. Hydrogen shortened colonic transit, and that effect was more prominent in the proximal colon than distal colon.

Mapping white matter diffusion and cerebrovascular reactivity in carotid occlusive disease.

OBJECTIVE: To characterize the relationship between cerebrovascular reactivity (CVR) and white matter (WM) diffusion in patients with internal carotid artery (ICA) occlusive disease. METHODS: In this exploratory observational study, 41 patients with severe stenosis or occlusion of the extracranial ICA and 12 healthy control subjects underwent CVR mapping using the fMRI response to hypercapnia. Conventional anatomic and diffusion-weighted MRI sequences were used to calculate maps of the apparent diffusion coefficient (ADC) and to exclude areas of previous ischemic injury. In all subjects, ADC was compared between WM with positive and negative CVR. In 27 patients with unilateral ICA involvement, ADC and CVR were compared between ipsilateral and contralateral WM while covarying for relevant clinical risk factors. RESULTS: In patients with bilateral disease and in the ipsilateral hemisphere of patients with unilateral disease, negative CVR was associated with increased WM ADC (p < 0.01 and p < 0.005, respectively). In patients with unilateral disease, the ipsilateral CVR deficit was correlated with the degree of hemispheric WM ADC elevation (p < 0.005). ADC elevation remained significant after correction for potential confounding risk factors. CONCLUSIONS: CVR impairment is associated with ADC elevation in normal-appearing WM of patients with severe stenosis or occlusion of the extracranial ICA. This finding is consistent with the presence of early, low-grade ischemic injury.

Gravity Probe B: final results of a space experiment to test general relativity.

Gravity Probe B, launched 20 April 2004, is a space experiment testing two fundamental predictions of Einstein's theory of general relativity (GR), the geodetic and frame-dragging effects, by means of cryogenic gyroscopes in Earth orbit. Data collection started 28 August 2004 and ended 14 August 2005. Analysis of the data from all four gyroscopes results in a geodetic drift rate of -6601.8±18.3 mas/yr and a frame-dragging drift rate of -37.2±7.2 mas/yr, to be compared with the GR predictions of -6606.1 mas/yr and -39.2 mas/yr, respectively ("mas" is milliarcsecond; 1 mas=4.848×10(-9) rad).

Efficacy of the glucagon-like peptide-1 agonist exenatide in the treatment of short bowel syndrome.

BACKGROUND: Short bowel syndrome (SBS) is a serious clinical disorder characterized by diarrhea and nutritional deprivation. Glucagon-like peptide-1 (GLP-1) is a key hormone, produced by L-cells in the ileum, that regulates proximal gut transit. When extensive ileal resection occurs, as in SBS, GLP-1 levels may be deficient. In this study, we test whether the use of GLP-1 agonist exenatide can improve the nutritional state and intestinal symptoms of patients with SBS. METHODS: Five consecutive patients with SBS based on ≤90 cm of small bowel and clinical evidence of nutritional deprivation were selected. Baseline SBS symptoms, demographic and laboratory data were obtained. Antroduodenal manometry was performed on each subject. Each patient was then started on exenatide and over the following month, the baseline parameters were repeated. KEY RESULTS: The subjects consisted of four males and one female, aged 46-69 years. At baseline, all had severe diarrhea that ranged from 6 to 15 bowel movements per day, often occurring within minutes of eating. After exenatide, all five patients had immediate improvement in bowel frequency and form; bowel movements were no longer meal-related. Total parenteral nutrition was stopped successfully in three patients. Antroduodenal manometry revealed continuous low amplitude gastric contractions during fasting which completely normalized with exenatide. CONCLUSIONS & INFERENCES: Exenatide is a novel and safe treatment option for SBS. It produced substantial improvement in the bowel habits, nutritional status and quality of life of SBS patients. Successful treatment with exenatide may significantly reduce the need for parenteral nutrition and small bowel transplant.