Ultrasound Thickness Measurements Research Articles

Assessment of Reliability, Agreement, and Accuracy of Masseter Muscle Ultrasound Thickness Measurement Using a New Standardized Protocol.

There is no validated method of assessing masseter muscle thickness (MMT) by ultrasound imaging (US). However, this is important to ensure study and measurement quality of MMT by US in future studies, as MMT differs depending on the examined area. Thus, this study's aim was to present a new standardized method for assessing the MMT by US and to evaluate the reliability, consistency, and accuracy of its measurements. We also compared the results of MMT measurements obtained by US and computer tomography (CT). The study included nine healthy adults. The US and CT scans were collected in a supine rest position with the mandible in relaxed position. US measurements were determined according to a new standardized protocol (with precise probe location). The MMT measured by CT and US over a seven-day interval showed excellent intra-rater reliability. The mean MMT measured by CT was 12.1 mm (1.74) on the right side and 11.9 mm (1.61) on the left side. The mean MMT measured by US was 12.7 mm (2.00) on the right side and 11.5 mm (1.37) on the left side. The mean percent error in MMT measurement between CT and US was below 6%. A strong linear relationship was found between the CT and US measurements of the MMT on both body sides (p < 0.001, r ≥ 0.93). The proposed method of MMT measurement using US demonstrated excellent reliability, yielding results similar to those obtained from CT images. We recommend the use of this standardization protocol in further studies where precise assessment of MMT by US is expected.

Ultrasound measurement of traumatic scar and skin thickness: a scoping review of evidence across the translational pipeline of research-to-practice

ObjectivesTo identify the ultrasound methods used in the literature to measure traumatic scar thickness, and map gaps in the translation of these methods using evidence across the research-to-practice pipeline.DesignScoping review.Data...

Ultrasound Biofeedback Increases Abdominal Muscle Activation in Golfers With a History of Low Back Pain.

To compare activation ratios of the transverse abdominis (TrA) during an abdominal draw-in maneuver (ADIM) and abdominal obliques during a golf swing, with and without ultrasound biofeedback, and to determine intrarater reliability of these ultrasound thickness measures. Single-session crossover study. Laboratory. Sixteen adult golfers with 2 or more episodes of low back pain (LBP) in the past year. Verbal cueing alone and verbal cueing with ultrasound biofeedback. Bilateral TrA activation ratios were calculated during an ADIM with and without ultrasound biofeedback. Activation ratios of the abdominal obliques were calculated bilaterally during golf swings with and without ultrasound biofeedback. Intraclass correlation coefficients (ICCs) were calculated for average thickness across all muscles and conditions for the nonbiofeedback trials. Transverse abdominis activation ratios were significantly higher when ultrasound biofeedback was provided bilaterally ( P < 0.001). Abdominal oblique activation ratios during the golf swing were also significantly higher with ultrasound biofeedback for the lead ( P = 0.014) and trail ( P < 0.001) sides. Intraclass correlation coefficient values ranged from 0.92 to 0.97 ( P < 0.001). Ultrasound biofeedback can increase activation ratios of the TrA during a supine ADIM in adult golfers with a history of LBP. Postswing ultrasound biofeedback increases activation of the abdominal obliques during a golf swing in golfers with a history of LBP. Ultrasound thickness measures of the TrA and obliques have excellent intrarater reliability.

Reliability of Sonography Measures of the Lumbar Multifidus and Transversus Abdominis during Static and Dynamic Activities in Subjects with Non-Specific Chronic Low Back Pain.

Purpose: The purpose of this study was to investigate the test-retest reliability of ultrasound (US) thickness measurements and the muscle contraction ratio (CR) of lumbar multifidus (LM) and transversus abdominis (TA) muscles in participants with and without nonspecific chronic low back pain (NCLBP). Methods: A total of 62 participants (37 with NCLBP, 25 without NCLBP) with participated in the study. The within-day and between-day reliability of US thickness measurements and CR in a lying (supine for TA and prone for LM) and sitting positions for both muscles (sitting on a gym ball with both feet on the ground or lifting one foot off the floor) were assessed. Reliability analysis was performed with intraclass correlations (ICCs) for these two static and dynamic positions. Results: Test-retest reliability was calculated to be good to high for the static position (ICC = 0.72–0.95) and the dynamic position (ICC = 0.74–0.94) sonographic measurements in both group of TA measurement. Test-retest reliability of LM measurements was good to high for the static position (ICC = 0.82–0.95) and the dynamic position (ICC = 0.85–0.97) sonographic measurements in both groups. Conclusions: US imaging is a highly reliable method for the assessment of TA and LM thickness muscles in the dynamic position in participants with and without NCLBP. The CR measures may be adequately reliable in assessing the function of the TA and LM muscles in participants with NCLBP and healthy ones.

Expiratory Muscles, Neglected No More.

Expiratory Muscles, Neglected No More.

An apparatus for the continuous measurement of thickness during the electropolishing of superconducting cavities.

An apparatus allowing continuous acquisition of thickness measurements during electropolishing of superconducting cavities is described. The instrument is based on the ultrasound thickness measurement technique and allows the connection of up to six probes. The apparatus has been employed to monitor the surface treatment of PIP-II low beta single cell prototypes developed and manufactured by LASA-INFN and specifically to measure surface removal at different points of interest on the cavity surface. The apparatus facilitated the development and optimization of electropolishing parameters for incorporation into the cavity manufacturing process.

Ultrasound Measurement of Septic Shock-induced Acute Skeletal Muscle Atrophy in Intensive Care Unit.

Skeletal muscle wasting progresses rapidly during critical care. However, the effect of skeletal muscle changes on physical function during intensive care remain poorly understood. To examine the changes in skeletal muscle thickness of patients admitted to the intensive care unit (ICU) for septic shock and the relationship between skeletal muscle thickness and physical function following intensive care. Longitudinal observational study. Single emergency hospital. Ten septic shock patients who were mechanically ventilated in the ICU were recruited. Not applicable. Ultrasound measurements of thickness of rectus femoris (RF) were conducted within 24 hours after admission and repeated every two days until the 14th hospital day. The correlations between TRF and various parametric data (i.e., age, severity classification, mechanically ventilated period, length of stay (LOS) at the ICU, and physical function) correlations were assessed with Pearson's product moment coefficient of correlation. Curve estimation for best fit for chronological changes in TRF with respect to the HD and the correlation between TRF and clinical indicators. Eight septic shock patients were observed completely for 14 days. TRF decreased linearly by 30.6% (IQR: 23.9-45.7) during the first 14 days. The correlation between TRF at admission and physical function at the 30th hospital day was close to significant. The TRF at the 14th hospital day was negatively correlated with disease severity and age. A positive correlation was observed between the decrease in rate of TRF and LOS at the ICU. Skeletal muscle thickness of septic shock patients rapidly decreased in a linear manner over 14 days and may predict physical function after critical care.

Measuring of knee cartilage thickness: A comparison between ultrasound and magnetic resonance imaging methods

Cartilage diameter evaluation is critical for cartilage assessment. Magnetic resonance imaging (MRI) is the gold standard toolin cartilage evaluation. This observational and analytical study was designed to answer the question of whether there is arelationship between MRI and ultrasound in measuring cartilage thickness in the medial femoral condyle. The current study wasconducted at the Radiology Department of Rasole-Akram Hospital, Tehran, Iran, between March and May 2020. The samplesize was 18 people. The mean cartilage thickness of the left medial femoral cartilage was measured by T1 weighted MRI andultrasound from transverse, anterior, middle, and posterior medial femoral regions in nine healthy females with a mean ± stddeviation as indicated below: thickness = 1.6 ± 0.04 m, weight = 55.3 ± 4.3 kg, age = 21.7 ± 0.8 years.Additionally, nine healthy males with thickness = 1.80 ± 0.02 m, weight = 78.6 ± 11.1 kg, age = 22.4 ± 0.7 years were alsoincluded. Pearson and Bland–Altman plots were used for correlations and agreements. Anterior longitudinal ultrasoundthickness measures were significantly positively correlated with MRI anterior (r = 0.93, p = 0.00001), transverse ultrasoundwith MRI anterior (r = 0.87 p = 0.0369), middle longitudinal ultrasound with MRI anterior (r = 0.87 p = 0.00002), and transverseultrasound and MRI middle (r = 0.87 p = 0.00001).Agreement in all aspects was good except between the anterior longitudinal ultrasound and MRI posterior. There was a goodabsolute agreement between corresponding measurements done by ultrasound and MRI. The results suggest that ultrasound maybe a good clinical tool for assessing relative cartilage thickness in medial femoral regions.

Comparison of the lower uterine segment in pregnant women with and without previous cesarean section in 3\u2009T MRI

BackgroundPrenatal risk stratification of women with previous cesarean section (CS) by ultrasound thickness measurement of the lower uterine segment (LUS) is challenging. There is a wide range of proposed cutoff values and a valuable algorithm for selection before birth is not available. Using 3 T magnetic resonance imaging (MRI), we aimed to identify possible shortcomings of the current protocols used for birth selection after CS. Therefore, we evaluated anatomic and morphologic differences of the LUS and its thickness in patients with CS and those without. Possible impact factors on LUS thickness were studied.MethodsWe retrospectively analyzed 3 T MRI scans of 164 pregnant women in their second or third trimester, with (patient group, n = 60) and without previous CS (control group, n = 104). Sagittal T2-weighted images were studied. Normal findings of the LUS in MRI, reliability of MRI measurements, as well as factors influencing LUS thickness were assessed. MRI findings were compared to intraoperative findings.ResultsMRI provided good intra- (ICC 0.872) and fair inter-rater reliability (ICC 0.643). The relationship of the LUS and the cesarean scar to the surrounding anatomical structures and also its morphology varied strongly in patients and controls. Scar identification was possible in only 9/60 (15.0%) patients. The LUS was thinner in patients (1.9 ± 0.7 mm) than in controls (2.7 ± 1.3 mm). An LUS thinning up to 1 mm was observed in 23% of women without a previous CS and in 34% of women with normal intraoperative findings. Suspicion of a uterine dehiscence (LUS thickness < 1 mm) was only found in the patient group (5/59 (8.5%)) and was intraoperatively confirmed. In controls, LUS thickness was influenced by fetal weight, gestational age and amniotic fluid amounts.ConclusionVariability in anatomy, thickness and morphology seem to limit common prenatal LUS imaging diagnostics. Therefore, we consider that diagnostic protocols must be re-evaluated and imaging should be adjusted to the individual patient conditions. Due to its independency of ultrasound limitations, an additional MRI might be useful for altered anatomy and impaired ultrasound conditions. An LUS thinning up to 1 mm might be a normal finding and should be further investigated as reference value.

Cesarean section scar in 3T magnetic resonance imaging and ultrasound: image characteristics and comparison of the methods.

Uterine rupture during labor is a rare but life-threatening complication after previous cesarean section (CS). Prenatal risk is assessed using ultrasound thickness measurement of the lower uterine segment (LUS). Due to inhomogeneous study results, however, clinical obstetrics still lacks for standard protocols and reliable reference values. As 3T magnetic resonance imaging (MRI) has not yet been sufficiently studied regarding LUS diagnostics after previous CS, we sought to evaluate its feasibility focusing on thickness measurements and typical characteristics of the CS-scar region in comparison to ultrasound and the intraoperative status. In this prospective study, 25 asymptomatic patients with one previous CS and inconspicuous ultrasound findings were included. An additional 3T MRI with either a T2-weighted Turbo-Spin-Echo or a Half Fourier-Acquired-Single-shot-Turbo-spin-Echo sequence in a sagittal orientation was performed. We analyzed categorical image quality, inter- and intra-rater reliability as well as anatomy, morphology and thickness of the LUS. Results were compared to ultrasound and intraoperative findings. MRI provided good to excellent image quality in all patients. The imaged structures presented with a high variability in anatomy and morphology. Image characteristics indicating the uterine scar were only found in 11/25 (44%) patients. LUS thickness measurements with MRI showed good inter- and intra-rater reliability but poor agreement with ultrasound. MRI is appropriate for additional LUS diagnostics in patients with previous CS. The strong individual variability of LUS-anatomy and morphology might explain the difficulties in establishing uniform diagnostic standards after CS.

Parasternal intercostal muscle ultrasound in chronic obstructive pulmonary disease correlates with spirometric severity

In chronic obstructive pulmonary disease (COPD), loss of computed tomography (CT)-measured intercostal mass correlates with spirometric severity. Intercostal muscle ultrasound offers a repeatable and radiation-free alternative, however requires validation. We aimed to determine the reliability of parasternal intercostal muscle ultrasound, and the concurrent validity of parasternal ultrasound with clinicometric parameters. Twenty stable COPD patients underwent ultrasound measurement of thickness and echogenicity of 2nd and 3rd parasternal intercostal muscles, dominant pectoralis major and quadriceps, and diaphragm thickness; spirometry; and chest CT. Intra-rater intraclass correlation (ICC) for ultrasound intercostal thickness was 0.87–0.97 depending on site, with echogenicity ICC 0.63–0.91. Inter-rater ICC was fair to excellent. Ultrasound intercostal thickness moderately correlated with FEV1% predicted (r = 0.33) and quadriceps thickness (r = 0.31). Echogenicity correlated negatively with FEV1% predicted (r = −0.32). CT-measured lateral intercostal mass correlate negatively with parasternal ultrasound intercostal thickness. These data confirm ultrasound of parasternal intercostal musculature is reproducible. Lower intercostal muscle quantity and quality reflects greater COPD spirometric severity. This novel tool may have biomarker potential for both the systemic effects of COPD on muscle as well as local disruption of respiratory mechanics. The negative correlation between CT and ultrasound measurements may reflect complex site-dependent interactions between respiratory muscles and the chest wall.

Can ultrasound measures of intrinsic foot muscles and plantar soft tissues predict future diabetes-related foot disease? A systematic review.

IntroductionDiabetes mellitus (DM) is associated with hyperglycaemia and advanced glycosylation end-products. In the foot, the consequences of chronic or uncontrolled diabetes are micro and macrovascular disease, neuropathy, reduced joint mobility and structural and soft tissue changes that increase the risk of ulcer development and amputation. Diabetes foot assessment currently includes a comprehensive history, neurological and vascular assessments and examination focussed on dermatological and musculoskeletal abnormalities. Whilst these assessments are helpful for predicting ulceration risk, direct identifiers that enable early therapeutic intervention are lacking. The intention of this review was to ascertain if B-mode ultrasound could be clinically applied to identify structural change in the diabetic foot and be utilised as an early predictor of ulceration risk.MethodsPrimary databases and grey literature sources were systematically searched. Selection criteria were that the study included a diabetic sample and used B-mode ultrasound to assess soft tissue structures of the foot (plantar skin, plantar fat pad or intrinsic muscles).ResultsFifteen studies were identified for inclusion (combined diabetic sample of 773). Ultrasound demonstrated reductions in tissue thickness in diabetics compared to non-diabetics under first (p = 0.01) and second (p = 0.03) metatarsal heads, but not the third (p = 0.24). Statistical heterogeneity was high for ultrasound thickness measures under metatarsal heads four/five (I2 65%, 81%) and very high for plantar skin (I2 98%), heel pad (I2 76%) and intrinsic muscles (I2 91%, 81%). Extensor digitorum brevis (EDB) ultrasound measures were significantly thinner in diabetics for all dimension measures compared to healthy controls except one study, which reported no significant differences in EDB thickness.ConclusionsNo direct evidence was found to indicate B-mode ultrasound measures can predict soft tissue changes in the plantar foot in diabetes, although low level studies indicate ultrasound has the potential to identify structural change. Clinical, methodological and statistical heterogeneity limit result applicability. This review highlights the need for robust prospective longitudinal research to examine the predictive validity of this method.

Proficiency test on thickness measurement using ultrasound: A metrological aid to improve safety in transportation of dangerous products

IntroductionSafely transporting dangerous products such as fuels and other chemicals depends mostly on the integrity of the tanks and vessels in which they are stored. Regular vehicular inspection using non-destructive testing is an important coadjutant to assure the quality and reliability of transportation vessels: for instance, thickness measurement using ultrasound equipment. Typically, vehicular inspections are done by accredited inspection bodies. One way to attest to the conformity of accredited inspection bodies is a proficiency test. This paper discloses a proficiency test in which accredited inspection bodies took part in performing ultrasound thickness measurement in tanker trucks and vessels used to transport dangerous products. MethodA total of 59 participants participated in the proficiency test. An artefact was developed for the proficiency test, consisting of metal-walled hollow cubes whose thickness ranged from 2 to 12 mm. To be approved, the participants were required to yield measurement results statistically equivalent to the reference value for all 6 walls of the cube assigned to it, partially approved for an equivalent measurement for 2 to 5 walls and disapproved with one or no equivalent results. The statistics used involved the Z-score (p = 0.95). ResultsFive participants failed to provide a result during the proficiency test (9%), 16 were approved (27%), 35 were partially approved (59%) and only 3 were disapproved (5%). ConclusionsThe proficiency test disclosed that measurement system calibration plays an important role among the successful accredited inspection bodies. Technical training on metrological issues, leading to professional and technical certification, would also improve the general performance for thickness measurement using ultrasound. Practical applicationsSafety in transporting dangerous products depends on the capability to perform a good technical evaluation of the integrity of vessels and tanks, which can be evaluated with the aid of a metrological tool, called a proficiency test.

Body Mass Normalization for Ultrasound Measurements of Adolescent Lateral Abdominal Muscle Thickness.

The purpose of this study was to determine the value of the allometric parameter for ultrasound measurements of the thickness of the oblique external (OE), internal (OI), and transversus abdominis (TrA) muscles in the adolescent population. The allometric parameter is the slope of the linear regression line between the log transformed body mass and log transformed muscle size measurement. The study included 321 adolescents between the ages of 10 and 17, consisting of 160 boys and 161 girls. The participants were recruited from local schools and attended regular school classes at normal grade levels. All individuals with no signs of scoliosis (screening with use of a scoliometer), and no surgical procedures performed on the trunk area were included. A real-time ultrasound B-scanner with a linear array transducer was used to obtain images of the lateral abdominal muscles from both sides of the body. The correlation between body mass and the OE muscle was r = 0.69; the OI muscle r = 0.68; and the TrA muscle r = 0.53 (in all cases, P < .0001). The allometric parameter for the OE was 0.88296; the OI 0.718756; and the TrA 0.60986. Using these parameters, no significant correlations were found between body mass and the allometric-scaled thickness of the lateral abdominal muscles. Significant positive correlations exist between body mass and lateral abdominal muscle thickness assessed by ultrasound imaging. Therefore, it is reasonable to advise that the values of the allometric parameters for OE, OI, and TrA obtained in this study should be used in other studies performed on adolescents.

Evaluation of knee cartilage thickness: A comparison between ultrasound and magnetic resonance imaging methods

BackgroundEstablishing clinically accessible measures of cartilage health is critical for assessing effectiveness of protocols to reduce risk of osteoarthritis (OA) development and progression. Cartilage thickness is one important measure in describing both OA development and progression. The objective was to determine the relationship between ultrasound and MRI measures of cartilage thickness in the medial femoral condyle. MethodsMean cartilage thicknesses of the left medial femoral cartilage were measured via T1 weighted MRI and ultrasound imaging from transverse, anterior, middle, and posterior medial femoral regions in 10 healthy females (Mean±Std Dev) (1.66±0.08m, 59.5±8.3kg, 21.6±1.4years) and nine healthy males (1.80±0.08m, 79.1±6.2kg, 21.7±1.5years). Pearson correlations examined relationships between MRI and ultrasound measures. Bland–Altman plots evaluated agreement between the imaging modalities. ResultsTransverse ultrasound thickness measures were significantly positively correlated with MRI middle (r=.67, P≤.05) and posterior thicknesses (r=.49, P≤.05) while the middle and posterior longitudinal ultrasound measures were significantly correlated to their respective MRI regions (r=.67, P≤.05 & r=.59 P≤.05, respectively). There was poor absolute agreement between correlated measures with ultrasound thickness measures being between 1.9 and 2.8mm smaller than MRI measures. ConclusionsThese results suggest that ultrasound may be a viable clinical tool to assess relative cartilage thickness in the middle and posterior medial femoral regions. However, the absolute validity of the ultrasound measure is called into question due to the larger MRI-based thickness measures. Level of evidenceLevel IV.

Relationship between flexion-rotation test and ultrasound thickness measurement of the abdominal muscles.

The purpose of this study was to investigate the relationship between flexion-rotation test and ultrasound (US) thickness measurement of the antero-lateral abdominal muscles. Following ethical approval, a convenience sample of 55 subjects between the ages of 20 and 30 years participated in this study. Endurance of the abdominal muscles was measured using the flexion-rotation test in all subjects. US thickness measurement for the transversus abdominis (TrA), internal oblique (IO) and external oblique (EO) muscles was performed on the right side at rest in a supine position. Pearson correlation coefficient between the variables of the study showed no significant relationship between the flexion-rotation test and US thickness measurements of the TrA (r = -0.03, P = 0.80), IO (r = -0.13, P = 0.32), and EO (r = -0.14, P = 0.31) muscles. The significance level of 0.05 was chosen. It seems that there is no significant relationship between the flexion-rotation test and US measurement of abdominal muscles thickness.

The contribution of glycosaminoglycans to the mechanical behaviour of the posterior human sclera.

We characterized the structural and mechanical changes after experimental digestion of sulfated glycosaminoglycans (s-GAGs) in the human posterior sclera, using ultrasound thickness measurements and an inflation test with three-dimensional digital image correlation (3D-DIC). Each scleral specimen was first incubated in a buffer solution to return to full hydration, inflation tested, treated in a buffer solution with chondroitinase ABC (ChABC), then inflation tested again. After each test series, the thickness of eight locations was measured. After enzymatic treatment, the average scleral thickness decreased by 13.3% (p < 0.001) and there was a stiffer overall stress-strain response (p < 0.05). The stress-strain response showed a statistically significant increase in the low-pressure stiffness, high-pressure stiffness and hysteresis. Thus, s-GAGs play a measurable role in the mechanical behaviour of the posterior human sclera.

Photodynamic Therapy for Choroidal Metastasis

To evaluate the effectiveness of photodynamic therapy (PDT) in the management of choroidal metastasis. Retrospective, interventional case series. Patients with choroidal metastasis treated with PDT at a single institution were reviewed. PDT was applied with verteporfin at a dose of 6 mg/m(2) body surface area and a 689 nm diode laser for 83 seconds. Visual acuity, tumor basal diameter, tumor thickness by ultrasonography, and enhanced depth imaging optical coherence tomography (EDI-OCT), as well as associated features including subretinal fluid, were recorded before PDT and during follow-up examinations. Twenty-one tumors in 13 eyes of 10 patients were included. Eight tumors were treated with a single session of PDT, 11 tumors received 2 sessions, 1 tumor received 3 sessions, and 1 tumor received 5 sessions. At the end of a mean follow-up of 12 months (range, 3-42 months), 9 eyes (69%) had stable or improved visual acuity, while 4 eyes (31%) had decreased visual acuity. Mean logMAR change in visual acuity was -0.09 (range, -1.3 to 0.8). Seventeen of 21 tumors (81%) were flat at last follow-up. The mean decrease in ultrasound-measured thickness was 0.83 mm (range, 2.6 mm decrease to 1.4 mm increase), while the decrease in EDI-OCT-measured thickness was 400 μm (range, 1280 μm decrease to 280 μm increase). Eighteen tumors (86%) had complete resolution of subretinal fluid. There were no PDT-related complications. Photodynamic therapy may be an effective therapeutic option for the management of choroidal metastasis in selected cases.

The Relationship Between the Side-Lying Endurance Test and Ultrasound Thickness Measurement for Abdominal Muscles

Background: Low Back Pain (LBP) is a common musculoskeletal disorder in the different societies. Objectives: The purpose of this study was to investigate the relationship between the side-lying endurance test and ultrasound thickness measurement of the anterolateral abdominal muscles. Patients and Methods: A convenience sample of 55 subjects, aged 20 - 30 years, participated in this study. Endurance of abdominal muscles was measured using side-lying endurance test in all subjects. Ultrasound thickness measurement for the Transverses Abdominis (TVA), Internal Oblique (IO), and External Oblique (EO) muscles was performed on the right side at rest in supine position. Results: The results of the Pearson correlation coefficient between the variables of the study showed no significant relationship between the side-lying endurance test and ultrasound thickness measurements of TVA (r = 0.06, P = 0.65), IO (r = 0.06, P = 0.62), and EO (r = 0.08, P = 0.54) muscles. The significance level of 0.05 was chosen. Conclusions: It seems that there is no significant relationship between the side-lying endurance test and abdominal muscles thickness.

Reliability of ultrasound thickness measurement of the abdominal muscles during clinical isometric endurance tests

The study was designed to evaluate the intra-examiner reliability of ultrasound (US) thickness measurement of abdominal muscles activity when supine lying and during two isometric endurance tests in subjects with and without Low back pain (LBP). A total of 19 women (9 with LBP, 10 without LBP) participated in the study. Within-day reliability of the US thickness measurements at supine lying and the two isometric endurance tests were assessed in all subjects. The intra-class correlation coefficient (ICC) was used to assess the relative reliability of thickness measurement. The standard error of measurement (SEM), minimal detectable change (MDC) and the coefficient of variation (CV) were used to evaluate the absolute reliability. Results indicated high ICC scores (0.73-0.99) and also small SEM and MDC scores for within-day reliability assessment. The Bland-Altman plots of agreement in US measurement of the abdominal muscles during the two isometric endurance tests demonstrated that 95% of the observations fall between the limits of agreement for test and retest measurements. Together the results indicate high intra-tester reliability for the US measurement of the thickness of abdominal muscles in all the positions tested. According to the study's findings, US imaging can be used as a reliable method for assessment of abdominal muscles activity in supine lying and the two isometric endurance tests employed, in participants with and without LBP.