Quantitative Magnetic Resonance Analysis Research Articles

Energetics of migratory bats during stopover: a test of the torpor-assisted migration hypothesis.

The torpor-assisted migration hypothesis posits that migration is facilitated in bats by the use of torpor during stopover roosting periods, and predicts that at stopover, bats regulate time in torpor facultatively so that daily energy expenditure is independent of ambient roosting temperature. Energy savings can thus be directed to migratory movement. However, direct measurements of total roosting energy expenditure in relation to ambient and body temperature are lacking. We captured migratory silver-haired bats (Lasionycteris noctivagans; ∼11 g) at Long Point, ON, Canada, in spring and autumn 2016. We used quantitative magnetic resonance analysis to measure body composition change and energy expenditure over a 12h roosting period in a ventilated incubator at 10, 17 and 25°C. We assessed the effects of season, body mass, sex and age on energy expenditure. We found that daily energy expenditure was independent of roosting temperature, and that this was achieved by flexible use of torpor. Variation in body mass at capture was driven mainly by differences in fat, and the amount of body fat was negatively related to torpor use, particularly in spring. Season, sex and age also affected torpor use and energy expenditure, notably with pregnant females being generally fatter and using less torpor than males in spring. We estimate that stopover contributes only 15-20% to the total energy costs of migration in bats compared with 70% or more in typical birds. This study provides support for the torpor-assisted migration hypothesis, and furthers our understanding of the energy budgets of migratory bats.

Scanning Snakes to Measure Condition: A Validation of Quantitative Magnetic Resonance

Abstract Body composition is a measure of an animal's energetic state that can inform many research fields, yet the analysis traditionally requires individuals to be killed, and chemical analysis is labor intensive. Quantitative magnetic resonance (QMR) measures body composition noninvasively in live and nonanesthetized animals. Our aim was to validate QMR analysis for snakes by comparing it with gravimetric chemical analysis. We collected Northern Watersnakes (Nerodia sipedon sipedon) and Eastern Massasaugas (Sistrurus catenatus catenatus) that were found dead on roads, analyzed their body composition using the QMR scanner, and then by gravimetric chemical analysis. We compared fat mass, wet lean mass, and total water mass between the two methods, and then calculated bias, absolute error (g), and relative error (%) of the QMR analysis. Body composition values from the QMR analyses were highly correlated with the values obtained by gravimetric chemical analysis. Bias and errors were reasonable for wet lea...

A field test of the effects of body composition analysis by quantitative magnetic resonance on songbird stopover behaviour

Quantitative magnetic resonance (QMR) is a non-invasive technology used to measure body composition. It has great potential to advance the study of energetics and fuel use of migratory birds. However, there is concern that exposure to a strong magnetic field during QMR analysis could affect magnetite-based geomagnetic senses of migratory songbirds which may be important for orientation and navigation. We used radiotelemetry and capture-mark-recapture analysis to test for effects of QMR analysis on stopover duration and departure orientation. There was no evidence from radiotelemetry data that QMR analysis influenced minimum stopover duration or departure orientation of Black-throated Blue Warblers (Setophaga caerulescens) in the spring or fall, or Magnolia Warblers (Setophaga magnolia) in the spring. Capture-mark-recapture analysis of White-throated Sparrow (Zonotrichia albicollis) ringing data showed no effects of QMR on transiency or recapture probability, but a slight increase in estimated stopover duration (days) in the fall. Our study provides evidence that stopover duration and departure orientation of migrating songbirds are not significantly affected by QMR analysis with the exception of fall stopover duration estimates from mark-recapture models, and that QMR is a safe technique for the study of birds in the field.

The relationships between quantitative MR parameters in hippocampus in healthy subjects and patients with temporal lobe epilepsy.

We introduce a new magnetic resonance (MR) method based on a pixel-by-pixel image processing to examine relationships between metabolic and structural processes in the pathologic hippocampus. The method was tested for lateralization of the epileptogenic zone in patients with temporal lobe epilepsy (TLE). Twenty patients with drug-resistant TLE and fifteen healthy controls were examined at 3T. The measurement protocol contained T2-weighted MR images, spectroscopic imaging, diffusion tensor imaging and T2 relaxometry. Correlations between quantitative MR parameters were calculated on a pixel-by-pixel basis using the CORIMA program which enables automated pixel identification in the normal tissue according to control data. All MR parameters changed in the anteroposterior direction in the hippocampus and correlation patterns and their slopes differed between patients and controls. Combinations of T2 relaxation times with metabolite values represent the best biomarkers of the epileptogenic zone. Correlations with mean diffusivity did not provide sufficiently accurate results due to diffusion image distortions. Quantitative MR analysis non-invasively provides a detailed description of hippocampal pathology and may represent complementary tool to the standard clinical protocol. However, the automated processing should be carefully monitored in order to avoid possible errors caused by MR artifacts.

No Trade-Offs between Lipid Stores and Structural Growth in Juvenile Zebra Finches Undergoing Nutritional Stress during Development.

Nutritional conditions during development can affect both structural growth and body fat deposition. Body size and body fat each have significant consequences for fitness, yet few studies have investigated how young birds balance resource allocation between structural growth and fat reserves. We raised zebra finches (Taeniopygia guttata) in consistently high- or low-food conditions until posthatch day 35 (PHD 35). From this age until PHD 62, half of the birds in each condition were switched to the other treatment, while the rest were maintained on the same conditions. Body mass, lean mass, body fat, and tarsus length were measured before (PHD 25) and after (PHD 55) nutritional independence. Precise measures of body composition were obtained noninvasively at both ages using quantitative magnetic resonance analysis. At PHD 25, birds in the high treatment had more body mass and lean mass than birds in the low treatment, but nutritional treatments did not affect body fat at this age. Unexpectedly, the strategic response of birds that experienced deteriorating food availability was to maintain body mass by increasing body fat and decreasing lean mass. Birds that experienced an improvement in food availability significantly increased body mass by increasing lean mass and not body fat. Birds maintained on a low diet throughout did not significantly increase body mass, lean mass, or body fat. Tarsus length was not affected by nutritional manipulations. These findings indicate that nutritional stress did not affect the relationship between skeletal growth and body fat deposition because lean mass, body fat, and tarsus length can be independently regulated at different developmental periods depending on nutritional conditions.

Genetically-based behavioural morph affects stopover refuelling performance in white-throated sparrowsZonotrichia albicollis

Intraspecifi c competition can infl uence refuelling at migration stopover sites. White-throated sparrows Zonotrichia albicollis have genetically-determined plumage morphs that diff er in dominance behaviour and competitive abilities. Th is study examines the eff ects of plumage morph, sex and age, three likely indicators of competitive ability, on fall migration timing, body composition, and refuelling rates during stopover at Long Point, Ontario. We used quantitative magnetic resonance analysis and plasma metabolite profi ling to determine body composition and refuelling rates, respectively. We determined sex and plumage morph genetically. Competitive ability did not infl uence migration timing. Controlling for structural size, males had larger lean mass than females, but we found no diff erences in body fat or lean mass between plumage morphs. Plasma metabolite concentrations indicated that the aggressive white-stripe morph refuelled faster than the less aggressive tan-stripe morph, though there were no diff erences among sex and age groups. We suggest that increased refuelling rates did not result in increased fat or lean mass because 1) individuals categorised as less competitive had longer stopover durations to compensate for slower refuelling rates; or 2) costs of behaving more competitively off set gains from faster refuelling rates.

Quantitative magnetic resonance: a rapid, noninvasive body composition analysis technique for live and salvaged bats

Quantitative magnetic resonance (QMR) is a new technology for measuring body composition of live, nonanesthetized animals (fat mass, lean mass, and total body water) in 4 min or less. We conducted a validation study to compare QMR body composition analysis of 3 species of bats (mass range 5.77–31.30 g) with traditional chemical extraction. In addition to scans of live animals, we tested the effectiveness of QMR for salvaged specimens (bats killed by wind turbines) and the effects of carcass temperature. Our analysis indicates that QMR body composition analysis is effective for live and salvaged animals. Frozen carcasses could not be analyzed, but results were not dramatically affected for specimens at 4u Ca nd 37uC. QMR analysis eliminates the need to euthanize animals to determine body composition precisely, allows rapid and efficient data collection, and makes it possible to follow individuals longitudinally through time. DOI: 10.1644/10-MAMM-A-051.1.

Quantitative magnetic resonance analysis and a morphometric predictive model reveal lean body mass changes in migrating Nearctic–Neotropical passerines

Most studies of lean mass dynamics in free-living passerine birds have focused on Old World species at geographical barriers where they are challenged to make the longest non-stop flight of their migration. We examined lean mass variation in New World passerines in an area where the distribution of stopover habitat does not require flights to exceed more than a few hours and most migrants stop flying well before fat stores near exhaustion. We used either quantitative magnetic resonance (QMR) analysis or a morphometric model to measure or estimate, respectively, the fat and lean body mass of migrants during stopovers in New York, USA. With these data, we examined (1) variance in total body mass explained by lean body mass, (2) hourly rates of fat and lean body mass change in single-capture birds, and (3) net changes in fat and lean mass in recaptured birds. Lean mass contributed to 50% of the variation in total body mass among white-throated sparrows Zonotrichia albicollis and hermit thrushes Catharus guttatus. Lean mass of refueling gray catbirds Dumetella carolinensis and white-throated sparrows, respectively, increased 1.123 and 0.320gh(-1). Lean mass of ovenbirds Seiurus aurocapillus accounted for an estimated 33-40% of hourly gains in total body mass. On average 35% of the total mass gained among recaptured birds was lean mass. Substantial changes in passerine lean mass are not limited to times when birds are forced to make long, non-stop flights across barriers. Protein usage during migration is common across broad taxonomic groups, migration systems, and migration strategies.

Patch-based segmentation using expert priors: Application to hippocampus and ventricle segmentation

Quantitative magnetic resonance analysis often requires accurate, robust, and reliable automatic extraction of anatomical structures. Recently, template-warping methods incorporating a label fusion strategy have demonstrated high accuracy in segmenting cerebral structures. In this study, we propose a novel patch-based method using expert manual segmentations as priors to achieve this task. Inspired by recent work in image denoising, the proposed nonlocal patch-based label fusion produces accurate and robust segmentation. Validation with two different datasets is presented. In our experiments, the hippocampi of 80 healthy subjects and the lateral ventricles of 80 patients with Alzheimer's disease were segmented. The influence on segmentation accuracy of different parameters such as patch size and number of training subjects was also studied. A comparison with an appearance-based method and a template-based method was also carried out. The highest median kappa index values obtained with the proposed method were 0.884 for hippocampus segmentation and 0.959 for lateral ventricle segmentation.

Head Trauma and Intellectual Status: Relation to Quantitative Magnetic Resonance Imaging Findings

This article contrasts 2 groups that sustained somewhat similar moderate to severe closed-head traumatic brain injury (TBI), but were deliberately selected to be different with regard to postinjury intellectual status--one group average or above, the other below. The purpose of this comparison was to describe any morphological characteristics of the 2 groups ascertained from quantitative magnetic resonance (QMR) imaging. Thirty-five TBI participants with Full Scale IQ (FSIQ) less than or equal to 90 were compared to 33 TBI participants whose FSIQ was above 90. A group of normal volunteer participants, age and gender matched, constituted a third magnetic resonance comparison group. All participants received uniform MRI from which QMR analysis was performed, including total cranial volume, subarachnoid cerebral spinal fluid ventricular volume, and hippocampal volume. Both TBI groups received neuropsychological testing in the course of clinical follow-up. Morphological comparisons between groups were made using multivariate analysis of variance. The TBI group with an IQ less than or equal to 90 had significantly enlarged third and temporal horn compartments. Total intracranial volume was smaller in this group as well. Lower psychometric intelligence postinjury may be associated with more temporal lobe atrophy and subcortical pathology. Smaller premorbid brain size may be another risk factor.

Quantitative magnetic resonance imaging in the assessment of degenerative disc disease.

Understanding degenerative intervertebral disc diseases hinges on the ability to objectively and noninvasively assess the disc matrix composition and integrity. The potential of quantitative magnetic resonance imaging to meet these demands was evaluated. Analyzing the T1 and T2 signal patterns in the nucleus pulposus with increasing Thompson morphological grade revealed a significant reduction related to grade. This significant decrease in T1 and T2 in the nucleus pulposus with grade 4 degeneration and the corresponding low correlation coefficients with respect to the content of individual matrix molecules suggest that matrix integrity plays an important and distinct role in determining T1 and T2 signal. Similarly, the significant increase in magnetization transfer in the nucleus pulposus observed in grade 4 degeneration did not correlate with the changes in molecular content in these highly degenerated discs. Again, this lack of correlation clearly indicates that the tissue integrity and matrix composition independently contribute to the magnetization transfer signal. This study presents the first clear evidence that quantitative magnetic resonance analysis reflects not only the disc matrix composition, but also the structural integrity of the matrix of the disc.

Quantitative magnetic resonance analysis in vascular dementia.

The potential role of magnetic resonance imaging (MRI) in differentiating between specific causes of cognitive decline in patients with vascular dementia (VD) has not yet been fully established. We therefore decided to assess the supratentorial cerebral contents in 24 patients with a diagnosis of probable VD and in 24 normal subjects, matched for age and education level, using MRI volumetric parameters obtained by means of a quantitative method. The volumes of subarachnoid and ventricular spaces, cerebral tissue, and hyperintense areas on T2-weighted images were calculated. In order to reduce interindividual variability caused by differences in intracranial size, each absolute measurement was normalized to the relative size of the intracranial volume. In addition, we calculated the ratio between the areas of the corpus callosum (CC) and supratentorial brain at the same level on the T1-weighted image midsagittal plane. The MRI data were correlated with the deterioration of cognitive functions. Patients with VD showed significantly lower cerebral tissue volume and CC area, and higher ventricular space volume than normal subjects. Furthermore, the total volume of the T2 signal alterations was higher in VD patients than in normal subjects. In VD patients, this volume was found to be proportional to the increase in the volume of the ventricular space. On the other hand, no correlation was found between the volume of the T2 signal alterations and the area of the CC. The degree of global cognitive dysfunction and the score of each neuropsychological test did not show any correlation with the MRI data. Our results suggest that ventricular enlargement in VD patients is correlated with the increase in volume of the T2 signal abnormalities, but that the degree of global cognitive dysfunction is not influenced by the volume of these T2 signal abnormalities. Furthermore, the CC atrophy does not influence the score of any neuropsychological test or the degree of global cognitive dysfunction.

Sequential quantitative MR analysis of bone marrow: differences during treatment of lymphoid versus myeloid leukemia.

To assess the use of bulk T1 measurements with magnetic resonance (MR) imaging for monitoring treatment response in leukemic patients, with separate analysis of patients with acute lymphoid (ALL) and those with acute myeloid leukemia (AML). Bulk T1 values were determined repeatedly during the first 4 weeks of treatment in 16 patients with ALL (age range, 16-72 years) and the first 6 weeks of treatment in 51 patients with AML (age range, 17-75 years). Bulk T1 values were compared in all patients with AML or ALL and in those who did or did not respond to treatment. MR imaging of lumbar bone marrow demonstrated statistically significant differences in initial bulk T1 values and in changes in bulk T1 values during treatment between patients with ALL and those with AML. Changes in bulk T1 after the 2nd week of treatment were statistically significantly different between patients with and those without a response who had ALL but not in those with AML. Sequential quantitative MR imaging during treatment appears valuable for prediction of response in patients with ALL but not in those with AML. Further investigations are needed to determine what influence MR imaging can have on patient care, but patients with ALL should be analyzed separately from those with AML.