Effect of passive leg raising on the cross-sectional area of the right internal jugular vein in patients with obesity: a randomised controlled trial protocol.

BACKGROUND: Venous access in patients with obesity presents significant challenges. The success of central venous catheterisation largely depends on the cross-sectional area (CSA) of the internal jugular vein (IJV). While techniques like the Trendelenburg position have been traditionally used to increase IJV CSA, recent studies suggest its ineffectiveness in patients with obesity. Conversely, the potential of the effect of passive leg raising (PLR) has not been thoroughly investigated in this group of patients. METHODS: This protocol outlines a planned randomised controlled trial to evaluate the effect of PLR on the CSA of the IJV in patients with obesity slated for central venous catheterisation. The protocol involves dividing 40 participants into two groups: one undergoing PLR and another serving as a control group without positional change. The protocol specifies measuring the CSA of the IJV via ultrasound as the primary outcome. Secondary outcomes will include the success rates of right IJV cannulation. The proposed statistical approach includes the use of t-tests to compare the changes in CSA between the two groups, with a significance threshold set at p<0.05. ETHICS APPROVAL: This study has been approved by the Institutional Review Board of Shanghai Tongren Hospital. All the participants will provide informed consent prior to enrolment in the study. Regarding the dissemination of research findings, we plan to share the results through academic conferences and peer-reviewed publications. Additionally, we will communicate our findings to the public and professional communities, including patient advocacy groups. TRIAL REGISTRATION NUMBER: ChiCTR: ChiCTR2400080513.

The usage of a modified straight-leg raise neurodynamic test and hamstring flexibility for diagnosis of non-specific low back pain: A cross-sectional study.

OBJECTIVES: The main purpose of this research study was to compare mean modified straight-leg raise test (mSLR) and hamstring muscle length (HL) between chronic non-specific low back pain (LBP) and healthy subjects to understand the possibility of neuropathic causes in LBP population as it may impact the diagnosis and treatment of LBP. Another purpose was to compare mean mSLR between those with lumbar nerve root impingement and those without as determine by magnetic resonance imaging (MRI). METHODS: The design of the study is cross sectional and included 32 subjects with ages ranging from 18-50 years old. Clinical exam objective measures were collected such as patient questionnaires, somatosensory tests, HL range of motion, and a mSLR test, and were compared to the findings from a structural lumbar spine MRI. RESULTS: There were no significant differences in mean HL angulation and mSLR angulation between LBP and healthy subjects (p>0.05). There was no significant difference in mean HL by impingement by versus no impingement (38.3±15.6 versus 44.8±9.4, p = 0.08, Cohen's d = 0.50). On the other hand, there was a significant difference in mean mSLR angulation by impingement (57.6.3±8.7 versus 63.8±11.6, p = 0.05, Cohen's d = 0.60). CONCLUSIONS: The mSLR test was found to be associated with lumbar nerve root compression, regardless of the existence of radiating leg symptoms, and showed no association solely with the report of LBP. The findings highlight the diagnostic dilemma facing clinicians in patients with chronic nonspecific LBP with uncorrelated neuroanatomical image findings. Clinically, it may be necessary to reevaluate the common practice of exclusively using the mSLR test for patients with leg symptoms. This study may impact the way chronic LBP and neuropathic symptoms are diagnosed, potentially improving treatment methods, reducing persistent symptoms, and ultimately improving disabling effects.

Diffusion tensor imaging combined with chemical shift-encoded sequence to quantify the adaptive changes of calf muscles in amateur marathoners.

PURPOSE: Calf muscles play an important role in marathon race, and the incidence of injury is high in this process. This study prospectively quantified diffusion tensor metrics, muscle fat fraction (MFF) and cross-sectional area (CSA) of calf muscles induced by endurance exercise in amateur marathoners, and the potential mechanisms underlying the changes in these parameters were analyzed. METHOD: In this prospective study, 35 marathoners (27 males, 8 females; mean age (standard deviation, SD), 38.92 (4.83) years) and 26 controls (18 males, 8 females; mean age (SD), 38.35 (6.75) years) underwent magnetic resonance imaging (MRI) from September 2022 to March 2023. The diffusion tensor eigenvalues (λ1, λ2, λ3), radial diffusivity (RD), fractional anisotropy (FA), MFF and CSA of calf muscles were compared between marathoners and controls. A binary logistic regression model with gender correction was performed analyze the relationship between marathon exercise and DTI parameters, CSA and MFF of calf muscles. RESULTS: Interobserver agreement was good (κ = 0.71). The results of binary logistic regression model with gender correction showed that the regression coefficients of FA values in anterior group of calf (AC), soleus (SOL), medial gastrocnemius (MG) and lateral gastrocnemius (LG) were negative, and the odds ratios (OR) were 0.33, 0.45, 0.35, 0.05, respectively (P < 0.05). The OR of RD in SOL and λ2 in external group of calf (EC) were relatively higher, 3.74 and 3.26, respectively (P < 0.05). CSA was greater in SOL of marathoners, with an OR value of 1.00(P < 0.05). The MFF in AC and LG was lower in marathoners and OR of two indexes were -0.69 and -0.59, respectively (P < 0.05). CONCLUSIONS: Diffusion tensor imaging (DTI) combined with chemical shift-encoded sequence can noninvasively detect and quantify the adaptive changes of calf muscle morphology, microstructure and tissue composition induced by long-term running training in amateur marathoners.

Rapid 2D 23Na MRI of the calf using a denoising convolutional neural network.

PURPOSE: 23Na MRI can be used to quantify in-vivo tissue sodium concentration (TSC), but the inherently low 23Na signal leads to long scan times and/or noisy or low-resolution images. Reconstruction algorithms such as compressed sensing (CS) have been proposed to mitigate low signal-to-noise ratio (SNR); although, these can result in unnatural images, suboptimal denoising and long processing times. Recently, machine learning has been increasingly used to denoise 1H MRI acquisitions; however, this approach typically requires large volumes of high-quality training data, which is not readily available for 23Na MRI. Here, we propose using 1H data to train a denoising convolutional neural network (CNN), which we subsequently demonstrate on prospective 23Na images of the calf. METHODS: 1893 1H fat-saturated transverse slices of the knee from the open-source fastMRI dataset were used to train denoising CNNs for different levels of noise. Synthetic low SNR images were generated by adding gaussian noise to the high-quality 1H k-space data before reconstruction to create paired training data. For prospective testing, 23Na images of the calf were acquired in 10 healthy volunteers with a total of 150 averages over ten minutes, which were used as a reference throughout the study. From this data, images with fewer averages were retrospectively reconstructed using a non-uniform fast Fourier transform (NUFFT) as well as CS, with the NUFFT images subsequently denoised using the trained CNN. RESULTS: CNNs were successfully applied to 23Na images reconstructed with 50, 40 and 30 averages. Muscle and skin apparent TSC quantification from CNN-denoised images were equivalent to those from CS images, with <0.9 mM bias compared to reference values. Estimated SNR was significantly higher in CNN-denoised images compared to NUFFT, CS and reference images. Quantitative edge sharpness was equivalent for all images. For subjective image quality ranking, CNN-denoised images ranked equally best with reference images and significantly better than NUFFT and CS images. CONCLUSION: Denoising CNNs trained on 1H data can be successfully applied to 23Na images of the calf; thus, allowing scan time to be reduced from ten minutes to two minutes with little impact on image quality or apparent TSC quantification accuracy.

Multiparametric Quantitative MRI of Peripheral Nerves in the Leg: A Reliability Study.

BACKGROUND: Patients with polyneuropathies typically have demyelination and/or axonal degeneration in peripheral nerves. Currently, there is a lack of imaging biomarkers to track the changes in these pathologies. PURPOSE: To develop and evaluate the reliability of a multiparametric quantitative magnetic resonance imaging (qMRI) method of peripheral nerves in the leg. STUDY TYPE: Prospective. SUBJECTS: Seventeen healthy volunteers (36.2 ± 13.8 years old, 9 males) with 10 of them scanned twice for test-retest. FIELD STRENGTH/SEQUENCE: 3 T, three-dimensional gradient echo and diffusion tensor imaging. ASSESSMENT: A qMRI protocol and processing pipeline was established for quantifying the following nerve parameters that are sensitive to myelin and axonal pathologies: magnetization transfer (MT) ratio (MTR), MT saturation index (MTsat), T2 *, T1 , proton density (PD), fractional anisotropy (FA), and mean/axial/radial diffusivities (MD, AD, and RD). The qMRI protocol also measures the volume of nerve fascicles (fVOL) and the fat fraction (FF) of muscles. STATISTICAL TESTS: The intersession reproducibility and inter-rater reliability of each qMRI parameter were assessed by Bland-Altman analysis and intraclass correlation coefficient (ICC). Pairwise Pearson correlation analyses were performed to investigate the intrinsic association between qMRI parameters. Distal-to-proximal variations were evaluated by paired t-tests with Bonferroni-Holm multiple comparison corrections. P < 0.05 was considered statistically significant. RESULTS: The MTR, MTsat, T2 *, T1 , PD, FA, AD, and fVOL of the sciatic and tibial nerves, and the FF of leg muscles, had an overall good-to-excellent test-retest agreement (ICC varying from 0.78 to 0.99). All the qMRI parameters had good-to-excellent inter-rater reliability (ICC > 0.80). The data demonstrated a pattern of distal-to-proximal changes of an increased nerve MTsat and FA, and a decreased nerve T1 , PD, MD, and RD, as well as a significantly increased muscle FF. DATA CONCLUSION: The proposed multiparametric qMRI method of the peripheral nerves is highly reproducible and provided healthy control data which will be used in developing monitoring biomarkers in patients with polyneuropathies. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 2.

Passive leg raising test using the carotid flow velocity-time integral to predict fluid responsiveness.

PURPOSE: The passive leg raising test (PLR) is a noninvasive method widely adopted to assess fluid responsiveness. We propose to explore if changes in the carotid flow assessed by echo-Doppler can predict fluid responsiveness after a PLR. METHODS: We conducted a performance diagnostic study in two intensive care units from Argentina between February and April 2022. We included patients with signs of tissular hypoperfusion that required fluid resuscitation. We labeled the patients as fluid responders when we measured, after a fluid bolus, an increase greater than 15% in the left ventricle outflow tract (LVOT) VTI in an apical 5-chamber view and we compared those results with the carotid flow (CF) velocity-time integral (VTI) from the left supraclavicular region in a semi-recumbent position and during the PLR. RESULTS: Of the 62 eligible patients, 50 patients (80.6%) were included. The area under the ROC curve for a change in CF VTI during the PLR test was 0.869 (95% CI 0.743-0.947). An increase of at least of 11% in the CF VTI with the PLR predicted fluid-responsiveness with a sensitivity of 77.3% (95% CI 54.6-92.2%) and specificity of 78.6% (95% CI 59-91.7%). The positive predictive value was 73.9% (95% CI 57.4-85.6%) and the negative predictive value was 81.5% (95% CI 66.5-90.7%). The positive likelihood ratio was 3.61 and the negative likelihood ratio was 0.29. CONCLUSION: An increase greater than 11% in CF VTI after a PLR may be useful to predict fluid responsiveness among critically ill patients.

Intraoperative Ultrasound for Extracting Deep-Seated Radio-Opaque Foreign Body from Calf: A Case Report.

CASE: A 50-year-old man presented with chronic refractory symptoms of radiating leg pain with muscle cramps because of a retained bullet in the calf after being shot in 1990. Radiographs confirmed the bullet lodged in posterolateral aspect of calf abutting proximal fibula. An intraoperative point-of-care ultrasound aided in accurate localization of bullet, thereby facilitating precise planning of surgical incision and subsequent removal. CONCLUSIONS: Ultrasound can be used as an alternative tool for safe surgical extraction of deep-seated metallic object with minimal tissue dissection, obviating the need for C-arm.

ACR Appropriateness Criteria® Sudden Onset of Cold, Painful Leg: 2023 Update.

Acute onset of a cold, painful leg, also known as acute limb ischemia, describes the sudden loss of perfusion to the lower extremity and carries significant risk of morbidity and mortality. Acute limb ischemia requires rapid identification and the management of suspected vascular compromise and is inherently driven by clinical considerations. The objectives of initial imaging include confirmation of diagnosis, identifying the location and extent of vascular occlusion, and preprocedural/presurgical planning. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Deep Learning Segmentation of Lower Extremities Radiographs for an Automatic Leg Length Discrepancy Measurement.

Leg length measurement is relevant for the early diagnostic and treatment of discrepancies as they are related with orthopedic and biomechanical changes. Simple radiology constitutes the gold standard on which radiologists perform manual lower limb measurements. It is a simple task but represents an inefficient use of their time, expertise and knowledge that could be spent in more complex labors. In this study, a pipeline for semantic bone segmentation in lower extremities radiographs is proposed. It uses a deep learning U-net model and performs an automatic measurement without consuming physicians' time. A total of 20 radiographs were used to test the methodology proposed obtaining a high overlap between manual and automatic masks with a Dice coefficient value of 0.963. The obtained Spearman's rank correlation coefficient between manual and automatic leg length measurements is statistically different from cero except for the angle of the left mechanical axis. Furthermore, there is no case in which the proposed automatic method makes an absolute error greater than 2 cm in the quantification of leg length discrepancies, being this value the degree of discrepancy from which medical treatment is required.Clinical Relevance- Leg length discrepancy measurements from X-ray images is of vital importance for proper treatment planning. This is a laborious task for radiologists that can be accelerated using deep learning techniques.

The Reliability and Validity of a Portable Three-Dimensional Scanning System to Measure Leg Volume.

(1) Background: The study examined the reliability (test-retest, intra- and inter-day) and validity of a portable 3D scanning method when quantifying human leg volume. (2) Methods: Fifteen males volunteered to participate (age, 24.6 ± 2.0 years; stature, 178.9 ± 4.5 cm; body mass, 77.4 ± 6.5 kg; mean ± standard deviation). The volume of the lower and upper legs was examined using a water displacement method (the criterion) and two consecutive 3D scans. Measurements were taken at baseline, 1 h post-baseline (intra-day) and 24 h post-baseline (inter-day). Reliability and validity of the 3D scanning method was assessed using Bland-Altman limits of agreement and Pearson's product moment correlations. (3) Results: With respect to the test-retest reliability, the 3D scanning method had smaller systematic bias and narrower limits of agreement (±1%, and 3-5%, respectively) compared to the water displacement method (1-2% and 4-7%, respectively), when measuring lower and upper leg volume in humans. The correlation coefficients for all reliability comparisons (test-retest, intra-day, inter-day) would all be regarded as 'very strong' (all 0.94 or greater). (4) Conclusions: The study's results suggest that a 3D scanning method is a reliable and valid method to quantify leg volume.

MRI-based volume measurement methods for staging primary lower extremity lymphedema: a single-center study of asymmetric volume difference-a diagnostic study.

BACKGROUND: Lower extremity lymphedema (LEL) staging is mainly assessed by systems that solely depend on physical examinations and lack quantitative assessment based on modern imaging. OBJECTIVE: To explore the value of MRI-based asymmetric volume measurements in the clinical staging of primary LEL. METHODS: 92 patients with unilateral primary LEL underwent MRI examinations to determine the volume of the mid-calf (Vcl) calculated using the clinical dermatome method as well as the total volume (Vmri), musculoskeletal volume (VM), and subcutaneous volume (VS) volume of the middle calves. The difference between Vmri (DVmri) and VS (DVS) of the affected and unaffected calves was obtained and defined as the asymmetric volume difference. Meanwhile, the volume of the mid-calf (Vcl) and the difference in volume (DVcl) were calculated using the clinical circumferential method. The relationship between the asymmetric volume difference and clinical staging was then evaluated. Interobserver consistency was assessed through the intraclass correlation coefficient (ICC). Volume comparisons between the three groups were performed using the one-way analysis of variance (ANOVA) or the Kruskal-Wallis test. Spearman's correlation was used to assess volume and clinical stage correlation. The receiver operating characteristic (ROC) curve was used to evaluate the value of asymmetric volume difference for clinical staging. RESULTS: The asymmetric volume difference was statistically significant in stage I compared to stages II and III (p < 0.05). The asymmetric volume difference (DVmri: r = 0.753; DVS: r = 0.759) correlated more with the clinical stage than the affected Vcl (r = 0.581), Vmri (r = 0.628), VS (r = 0.743), and DVcl (r = 0.718). The area under the ROC curve (AUC) for identifying the clinical stage by the asymmetric volume difference was greater than that for the affected Vcl, Vmri, VS, and DVcl, with DVS (AUC = 0.951) having the largest area under the curve to distinguish between stages I and II. CONCLUSION: MRI-based asymmetric volume difference is an adjunctive measure for LEL clinical staging with good reproducibility. DVS could be the best indicator for differentiating between stages I and II of primary LEL.

Three-dimensional skeletal muscle architecture in the lower legs of living human infants.

Little is known about the skeletal muscle architecture of living humans at birth. In this study, we used magnetic resonance imaging (MRI) to measure the volumes of ten muscle groups in the lower legs of eight human infants aged less than three months. We then combined MRI and diffusion tensor imaging (DTI) to provide detailed, high-resolution reconstructions and measurements of moment arms, fascicle lengths, physiological cross-sectional areas (PCSAs), pennation angles and diffusion parameters of the medial (MG) and lateral gastrocnemius (LG) muscles. On average, the total lower leg muscle volume was 29.2 cm3. The largest muscle was the soleus muscle with a mean volume of 6.5 cm3. Compared to the LG muscles, the MG muscles had, on average, greater volumes (by ∼35%) and greater PCSAs (by ∼63%) but similar ankle-to-knee moment arm ratios (∼0.1 difference), fascicle lengths (∼5.7 mm difference) and pennation angles (∼2.7° difference). The MG data were compared with data previously collected from adults. The MG muscles of adults had, on average, a 63-fold greater volume, a 36-fold greater PCSA, and 1.7-fold greater fascicle length. This study demonstrates the feasibility of using MRI and DTI to reconstruct the three-dimensional architecture of skeletal muscles in living human infants. It is shown that, between infancy and adulthood, MG muscle fascicles grow primarily in cross-section rather than in length.

The relationship between cartilage thickness and muscle thickness or leg length discrepancy in poliomyelitis sequelae.

OBJECTIVES: To evaluate the relationship between cartilage loss and differences in muscle thickness and/or leg length in poliomyelitis sequelae (PMS). Our study is the first to evaluate the relationship between cartilage loss and both muscle atrophy and leg length discrepancy in the same population. METHODS: 37 patients with PMS and 38 healthy controls were included. Talar and distal femoral cartilage thicknesses and gastrocnemius medialis and quadriceps femoris muscle thicknesses were measured via ultrasound. Leg length differences and manual muscle strength were also evaluated. RESULTS: The mean muscle thicknesses and cartilage thicknesses were thinner in the more affected legs than in the less affected legs in the patient group. All of the ultrasonographic measurements were thinner in the less affected legs of the patient group than in the right legs of the control group, except for the knee cartilage thicknesses. While there was a correlation between the cartilage thickness difference and the muscle thickness difference between the less and more affected legs in the patient group, there was no correlation between the cartilage thickness difference and leg length differences. CONCLUSIONS: Patients with PMS are predisposed to osteoarthritis. Talar and knee cartilage thicknesses may be more associated with the muscle thickness than the leg length discrepancy in PMS.

Carotid Artery Corrected Flow Time Measured by Wearable Doppler Ultrasound Accurately Detects Changing Stroke Volume During the Passive Leg Raise in Ambulatory Volunteers.

BACKGROUND: The change in the corrected flow time of the common carotid artery (ccFTΔ) has been used as a surrogate of changing stroke volume (SVΔ) in the critically-ill. Thus, this relatively easy-to-obtain Doppler measure may help clinicians better define the intended effect of intravenous fluids. Yet the temporal evolution of SVΔ and ccFTΔ has not been reported in volunteers undergoing a passive leg raise (PLR). METHODS: We recruited clinically-euvolemic, non-fasted, adult, volunteers in a local physiology lab to perform 2 PLR maneuvers, each separated by a 5 minute 'wash-out'. During each PLR, SV was measured by a non-invasive pulse contour analysis device. SV was temporally-synchronized with a wireless, wearable Doppler ultrasound worn over the common carotid artery that continuously measured ccFT. RESULTS: 36 PLR maneuvers were obtained across 19 ambulatory volunteers. 8856 carotid Doppler cardiac cycles were analyzed. The ccFT increased nearly ubiquitously during the PLR and within 40-60 seconds of PLR onset; the rise in SV from the pulse contour device was more gradual. SVΔ by +5% and +10% were both detected by a +7% ccFTΔ with sensitivities, specificities and areas under the receiver operator curve of 59%, 95% and 0.77 (p < 0.001) and 66%, 76% and 0.73 (p < 0.001), respectively. CONCLUSIONS: The ccFTΔ during the PLR in ambulatory volunteers was rapid and sustained. Within the limits of precision for detecting a clinically-significant rise in SV by a non-invasive pulse contour analysis device, simultaneously-acquired ccFT from a wireless, wearable ultrasound system was accurate at detecting 'preload responsiveness'.

Calf extra-Fascial compartment area affects calf muscle pumping action: an air plethysmography and computed tomography study.

OBJECTIVES: We aimed to elucidate whether lower limb extra-fascial compartment and muscle areas affect the calf muscle pumping action on lower limbs. METHOD: This study included 90 patients (180 limbs) who underwent preoperative air plethysmography (APG) and preoperative non-contrast computed tomography (CT) of the lower limbs for diagnosis of unilateral or bilateral primary varicose veins. A correlation between cross-sectional CT images and preoperative APG was confirmed. Cross-sectional CT was used to measure the extra-fascial compartment and muscle areas of the calf. The lower limbs were divided into two groups: those that were normal and those with primary varicose veins. RESULTS: The extra-fascial compartment area was significantly correlated with the ejection fraction in normal (r = 0.388, n = 53, p = 0.004) and varicose limbs (r = 0.232, n = 91, p = 0.027). CONCLUSIONS: In normal and varicose limbs, evaluation of ejection fraction, an indicator of muscle pumping, requires consideration of the extra-fascial compartment area.

Exercise-related leg muscle signal changes: assessment using diffusion-weighted MRI.

We aimed to detect physiologic changes of leg muscle signal on magnetic resonance (MR) diffusion-weighted imaging (DWI) in asymptomatic subjects after repetitive plantar flexion exercises. In this monocentric prospective study, DWI of both legs were performed at rest and after exercise periods (5 min, Ex5: and 10 min, Ex10) in 20 active healthy subjects (mean age 31 years). The exercise consisted in repetitive plantar flexion of the right foot using elastic band, the patient being sited directly on the MR table. Both visual semiquantitative evaluations and quantitative (apparent diffusion coefficient, ADC; fractional anisotropy, FA) were performed in 5 leg compartments. Visually, signal changes involved mainly the fibular and gastrocnemius muscles and were considered intense after Ex5 in 3 subjects, moderate only after Ex5 in 10, and moderate only after Ex10 in 4. No changes were visible in 3 subjects. Quantitative evaluation confirmed significant signal changes in the fibular (ADC: + 17.4%, p < 0.001; FA: -8.3%, p = 0.030) and gastrocnemius (ADC: + 13.7%, p < 0.001; FA: -11.4%, p < 0.001) muscles between rest and post-exercise MR. Plantar flexion exercises induce changes on DWI, especially in fibular and gastrocnemius muscles, which can be visually and quantitatively detectable in asymptomatic active subjects.Trial registrationEudraCT 2008-A00694-51.

Thigh muscles are more susceptible to age-related muscle loss when compared to lower leg and pelvic muscles.

BACKGROUND: A key hallmark of aging is the progressive loss of skeletal muscle mass. Due to limitations of the various methods typically applied to assess muscle mass, only limited information is available on age-related differences between various muscle groups. This study assessed differences in individual lower body muscle group volumes between healthy young and older males. METHODS: Lower body muscle mass assessments were performed in 10 young (age: 27 ± 4 y) and 10 older (age: 71 ± 6 y) healthy, male adults using Dual-energy X-ray Absorptiometry (DXA), single slice (thigh) Computed Tomography (CT), as well as Magnetic Resonance Imaging (MRI). Muscle volumes of all individual muscle groups in the lower body were assessed by MRI. RESULTS: Leg lean mass, as assessed with DXA, was not significantly different between older (9.2 ± 1.0 kg) and young (10.5 ± 2.0 kg) men (P = 0.075). Thigh muscle cross-sectional area, as assessed with CT, was significantly lower (by 13 %) in the older (137 ± 17 cm2) compared to young (157 ± 24 cm2) participants (P = 0.044). MRI-derived lower body muscle volume was also significantly lower (by 20 %) in older (6.7 ± 0.9 L) compared to young (8.3 ± 1.3 L) men (P = 0.005). This was primarily attributed to substantial differences in thigh (24 %), rather than lower leg (12 %) and pelvis (15 %) muscle volume in the older vs the young. Thigh muscle volume averaged 3.4 ± 0.5 L in older and 4.5 ± 0.7 L in young men (P = 0.001). Of all thigh muscle groups, the quadriceps femoris showed the most profound difference (30 %) between young (2.3 ± 0.4 L) and older (1.6 ± 0.2 L) men (P < 0.001). CONCLUSIONS: The most profound differences in lower body muscle volume between young and older men are observed in the thigh. Within the thigh muscle groups, the quadriceps femoris shows the largest difference in muscle volume between young and older men. Finally, DXA appears less sensitive when compared to CT and MRI to assess age-related differences in muscle mass.