Freehand 3DUS Research Articles

Validation of a scanning technique with minimal compression for measuring muscle volume with freehand 3D ultrasound

Freehand 3D ultrasound (3D-US) is a promising technique for measuring muscle volume but it requires gel pads or water tanks to limit probe compression on the skin which makes it hard to use in clinical applications. Our objectives were to measure the effect of different compressions on muscle volume in order to assess the clinical applicability of a minimal compression method for lower limb muscles. 4 muscles of the lower limb on 15 healthy volunteers were scanned with a new commercial freehand 3D-US setup accessible to clinical experimentators. Each muscle was scanned with 3 levels of compression: standard compression, minimal compression and gel pad (method validated against MRI). Volume was calculated using software segmentation tools. Acquisitions and segmentations were done by the same examiner. There was a significant impact of standard compression on volume measurements, but no difference between minimal compression and gel pad. Standard compression underestimated volume with a mean bias of 16 mL. For minimal compression, 75 % of measured differences were below the predefined clinically acceptable limits of 10 mL. Mean bias for this method was 1.1 mL. In conclusion, standard compression in freehand 3D-US induces a systematic bias in volume calculations. But, with a trained examiner and the necessary precautions to minimize compression, this bias could be abolished and become acceptable in clinical applications. When a high accuracy is required, gel pads could still be important to consider.

Fast fetal head compounding from multi-view 3D ultrasound.

The diagnostic value of ultrasound images may be limited by the presence of artefacts, notably acoustic shadows, lack of contrast and localised signal dropout. Some of these artefacts are dependent on probe orientation and scan technique, with each image giving a distinct, partial view of the imaged anatomy. In this work, we propose a novel method to fuse the partially imaged fetal head anatomy, acquired from numerous views, into a single coherent 3D volume of the full anatomy. Firstly, a stream of freehand 3D US images is acquired using a single probe, capturing as many different views of the head as possible. The imaged anatomy at each time-point is then independently aligned to a canonical pose using a recurrent spatial transformer network, making our approach robust to fast fetal and probe motion. Secondly, images are fused by averaging only the most consistent and salient features from all images, producing a more detailed compounding, while minimising artefacts. We evaluated our method quantitatively and qualitatively, using image quality metrics and expert ratings, yielding state of the art performance in terms of image quality and robustness to misalignments. Being online, fast and fully automated, our method shows promise for clinical use and deployment as a real-time tool in the fetal screening clinic, where it may enable unparallelled insight into the shape and structure of the face, skull and brain.

In vitro evaluation of a method to locate bony structures using freehand 3DUS

In vitro evaluation of a method to locate bony structures using freehand 3DUS

Effect of knee joint angle on individual hamstrings morphology quantified using free-hand 3D ultrasonography

Exercise responses and injury rates differ between individual hamstrings and this may be linked with their morphology. The aim of this study was to compare muscle length and tendon dimensions between the individual hamstrings at two knee joint angles using free hand three-dimensional ultrasound (3D US). Muscle-tendon length and distal tendon cross-sectional area (CSA), volume, length and echogenicity of biceps femoris long (BFlh) and short (BFsh) head, semimembranosus (SM) and semitendinosus (ST) of 16 individuals were measured using free-hand 3D US at 0° (full extension) and 45° of knee flexion. ST showed the greatest length than all muscles and BFsh the lowest (p < 0.05). No difference was observed between SM and BFlh length (p > 0.05). Of the four muscles, ST tendon was longer, with less volume and CSA but greater echogenicity than the other tendons. In contrast, SM and BFlh showed shorter tendons and lower echogenicity but a greater volume and CSA than ST (p < 0.05). Muscle and tendon lengthened from 45° to 0° knee flexion angle (p < 0.05) but this change was not statistically different between individual hamstrings (p > 0.05). Freehand 3D US indicated that hamstring muscle length and distal tendon dimensions differ between individual hamstrings. All muscles and tendons lengthened as the knee was extended but this change was similar for all individual hamstrings.

Reliability of human Achilles tendon stiffness measures using freehand 3-d ultrasound

Introduction: The Achilles tendon (AT) is the largest and strongest tendon in the human body and is subject to high forces during weight-bearing activities such as walking and running. Tendon stiffness, which is defined as resistance to elongation under load, is a key determinant of the efficiency of the triceps surae muscle output during human locomotion. Freehand three-dimensional ultrasound (3DUS) is a promising method for measuring stiffness of the Achilles tendon, and particularly the free AT (2-6 cm proximal to calcaneus), which is commonly injured. This study aimed to investigate the test-retest reliability and the smallest detectable change (SDC) of freehand 3DUS in measuring free AT stiffness in humans. Methods: The free Achilles tendon length of healthy participants (n=10) was scanned on the same day on two consecutive occasions (1 h apart) during rest and isometric planterflexion (PF) contractions at 20%, 40%, and 60% of maximum force. The slope of force-elongation curve over these force levels represented individual stiffness (N/mm). Relative reliability was assessed using the intra-class correlation coefficient (ICC) and absolute reliability was estimated with standard error of measurement (SEM), and smallest detectable change (SDC). Systematic bias in stiffness measures was explored by comparing test and retest distributions and Bland-Altman plots. Results: The test-retest reliability for free AT stiffness using freehand 3DUS was excellent [ICC= 0.994 (95% CI 0.978 to 0.999)]. The mean difference (SD) was -3.15 (± 26.6) N/mm, SEM was 18.82 N/mm, and SDC was 52.14 N/mm. The P-value for the difference between the means was = 0.72. The Bland and Altman plot showed no systematic bias within stiffness measures as data points were equally scattered around the mean difference (95% CI: -22.18-15.88) and within the 95% limits of agreement (LOA) = mean + (SD × 1.96). Discussion: The current study has established the reliability of freehand three-dimensional ultrasound for determining free AT stiffness in healthy humans. Freehand 3DUS could be implemented in research or clinical practice to measure and monitor changes in free AT stiffness that may occur with loading or as a consequence of tendon injury or pathology. Conflict of interest disclosure: The authors declare that they have no competing interests.

The reliability and validity of triceps surae muscle volume assessment using freehand three-dimensional ultrasound in typically developing infants.

This study assessed the intra-acquirer, intra- and inter-processor reliability, and validity of the in vivo assessment of the medial gastrocnemius (MG), lateral gastrocnemius (LG) and soleus (SOL) muscle volumes using freehand 3D ultrasound (3DUS) in typically developing infants. Reliability assessments of freehand 3DUS were undertaken in infants across three ages groups: three, six and twelve months of age, with validity testing completed against magnetic resonance imaging (MRI) in infants at 3months of age. Freehand 3DUS scanning was carried out by a single acquirer, with two independent processors manually segmenting images to render volumes. MRI images were segmented independently by a separate processor, with the volumes compared to those obtained via freehand 3DUS. Reliability was assessed using intraclass correlation (ICC), coefficient of variance (CV) and minimal detectable change (MDC) across each assessment time point. Validity was assessed using the limits of agreement. ICCs for intra-acquirer reliability of the acquisition process for freehand 3DUS ranged from 0.91 to 0.99 across all muscles. ICCs for intra-processor and inter-processor reliability for the segmentation process of freehand 3DUS ranged from 0.80 to 0.98 across all muscles. Acceptable levels of agreement between muscle volume obtained by freehand 3DUS and MRI were found for all muscles; however, freehand 3DUS overestimated muscle volume of MG and LG and underestimate the SOL compared with MRI, with average absolute differences of MG=0.3ml, LG=0.3ml and Sol=1.2ml. Freehand 3DUS is a reliable method for measuring in vivo triceps surae muscle volume in typically developing infants. We conclude that freehand 3DUS is a useful tool to assess changes in muscle volume in response to growth and interventions in infants.

Reliability of Human Achilles Tendon Stiffness Measures Using Freehand 3-D Ultrasound

Achilles tendon (AT) stiffness is an important property of both human locomotor performance and injury mechanics. Freehand 3-D ultrasound (3-DUS) is a promising method for measuring stiffness of the Achilles tendon, particularly the free AT (2–6 cm proximal to calcaneus), which is commonly injured. The aim of this study was to investigate the test–retest reliability of freehand 3-DUS in measuring free AT stiffness in humans. The free Achilles tendon length of healthy participants (n = 10) was scanned on the same day on two consecutive occasions (1 h apart) during rest and isometric plantar flexion contractions at 20%, 40% and 60% of maximum force. The slope of the force–elongation curve over these force levels represented individual stiffness (N/mm). Relative reliability was assessed using the intra-class correlation coefficient (ICC), and absolute reliability was estimated with the standard error of measurement (SEM) and smallest detectable change. Systematic bias in stiffness measures was explored by comparing test and retest distributions and Bland–Altman plots. The test–retest reliability of free AT stiffness measured using freehand 3-DUS was excellent [ICC = 0.994, 95% confidence interval [CI]: 0.978–0.999)]. The mean stiffness values at test (361.83 N/mm [170.77]) and retest (364.98 N/mm [168.57]) did not significantly differ (p = 0.72), and the smallest detectable change was 52.14 N/mm. The Bland–Altman plot indicated the absence of systematic bias (95% CI: –22.18 to 15.88). Freehand 3-DUS provides reliable and precise measures of tendon stiffness and can be used to detect small changes in free AT stiffness in response to load or tendon pathology.

Magnetic Resonance Imaging and Freehand 3-D Ultrasound Provide Similar Estimates of Free Achilles Tendon Shape and 3-D Geometry

The purpose of this study was to assess the similarity of free Achilles tendon shape and 3-D geometry between magnetic resonance imaging (MRI) and freehand 3-D ultrasound (3-DUS) imaging methods. Fourteen elite/sub-elite middle-distance runners participated in the study. MRI and 3-DUS scans of the Achilles tendon were acquired on two separate imaging sessions, and all 3-D reconstructions were performed using identical methods. Shape similarity of free Achilles tendon reconstructed from MRI and 3-DUS data was assessed using Jaccard index, Hausdorff distance and root mean square error (RMSE). The Jaccard index, Hausdorff distance and RMSE values were 0.76 ± 0.05, 2.70 ± 0.70 and 0.61 ± 0.10 mm, respectively. The level of agreement between MRI and 3-DUS for free Achilles tendon volume, length and average cross-sectional area (CSA) was assessed using Bland-Altman analysis. Compared to MRI, freehand 3-DUS overestimated volume, length and average CSA by 30.6 ± 15.8 mm3 (1.1% ± 0.6%), 0.3 ± 0.7 mm (0.6% ± 1.9%) and 0.3 ± 1.42 mm2 (0.4% ± 2.0%), respectively. The upper and lower limits of agreement between MRI and 3-DUS for volume, length and average CSA were −0.4 to 61.7 mm3 (−0.2% to 2.3%), −1.0 to 1.5 mm (−3.2% to 4.5%) and −2.5 to 3.1 mm2 (−3.5% to 4.3%), respectively. There were no significant differences between imaging methods in CSA along the length of the tendon. In conclusion, MRI and freehand 3-DUS may be considered equivalent methods for estimating shape and 3-D geometry of the free Achilles tendon. These findings, together with the practical benefits of being able to assess 3-D Achilles tendon shape and geometry in a laboratory environment and under isometric loading, make 3-DUS an attractive alternative to MRI for assessing 3-D free Achilles tendon macro-structure in future studies.

Validity and reliability of a freehand 3D ultrasound system for the determination of triceps surae muscle volume in children with cerebral palsy.

This study assessed the validity, intra-rater and inter-rater reliability of segmentation of invivo medial gastrocnemius (MG), lateral gastrocnemius (LG) and soleus (SOL) muscle volume measurement using a single sweep freehand 3D ultrasound (3DUS) in children with cerebral palsy (CP). The MG, LG and SOL of both limbs of 18 children with CP (age 8years 4months±1year 10months, 11 males, unilateral CP=9, bilateral CP=9, Gross Motor Functional Classification System I=11, II=7) were scanned using freehand 3DUS and magnetic resonance imaging (MRI). All freehand 3DUS and MRI images were segmented and volumes rendered by two raters. Validity was assessed using limits of agreement method. Intra-rater and inter-rater reliability was assessed using intra-class correlation (ICC), coefficient of variance (CV) and minimal detectable change (MDC). Freehand 3DUS overestimated muscle volume of the MG and LG by <0.3mL (1%) and underestimated SOL by <1.3mL (1.5%) compared with MRI. ICCs for intra-rater reliability of the segmentation process for the freehand 3DUS system and MRI for muscle volume were >0.98 and 0.99, respectively, for all muscles. ICCs for inter-rater reliability of the segmentation process for freehand 3DUS and MRI volumes were >0.96 and 0.98, respectively, for all muscles. MDCs for single rater freehand 3DUS and MRI were <4.0mL (14%) and 3.2mL (11%), respectively, in all muscles. Freehand 3DUS is a valid and reliable method for the measurement of lower leg muscle volume that can be measured with a single sweep in children with CP invivo. It can be used as an alternative to MRI for the detection of clinically relevant changes in calf muscle volume as the result of growth and interventions.

Evaluation Of freehand high-resolution 3-dimensional ultrasound of the median nerve.

In this study we evaluated freehand 3D ultrasound (3DUS) of the median nerve in comparison to 2D ultrasound (2DUS) and assessed the influence of tilting the transversal plane on cross-sectional area (CSA) measurement. Two examiners investigated the median nerves of 22 healthy subjects over a distance of 20 cm using 3DUS. Image quality and CSA were assessed at random points within the virtual 3D volume and compared with 2DUS. Image quality within the virtual 3D volume was good/sufficient/poor in 53.0%/40.2%/6.8% (examiner 1) and 21.6%/69.6%/8.8% (examiner 2), respectively. CSA measurements with 3DUS were smaller than with 2DUS (-12% and -17%; Wilcoxon test, P < 0.001). Interrater agreement for 3DUS and intermethod agreement between 2DUS and 3DUS were moderate. Stepwise tilting of the transversal plane increased CSA significantly. Freehand 3DUS of the median nerve over 20 cm is feasible and may help overcome some of the limitations and pitfalls of 2DUS. Muscle Nerve 55: 206-212, 2017.

Technical Note: Millimeter precision in ultrasound based patient positioning: experimental quantification of inherent technical limitations.

To identify the relevant technical sources of error of a system based on three-dimensional ultrasound (3D US) for patient positioning in external beam radiotherapy. To quantify these sources of error in a controlled laboratory setting. To estimate the resulting end-to-end geometric precision of the intramodality protocol. Two identical free-hand 3D US systems at both the planning-CT and the treatment room were calibrated to the laboratory frame of reference. Every step of the calibration chain was repeated multiple times to estimate its contribution to overall systematic and random error. Optimal margins were computed given the identified and quantified systematic and random errors. In descending order of magnitude, the identified and quantified sources of error were: alignment of calibration phantom to laser marks 0.78 mm, alignment of lasers in treatment vs planning room 0.51 mm, calibration and tracking of 3D US probe 0.49 mm, alignment of stereoscopic infrared camera to calibration phantom 0.03 mm. Under ideal laboratory conditions, these errors are expected to limit ultrasound-based positioning to an accuracy of 1.05 mm radially. The investigated 3D ultrasound system achieves an intramodal accuracy of about 1 mm radially in a controlled laboratory setting. The identified systematic and random errors require an optimal clinical tumor volume to planning target volume margin of about 3 mm. These inherent technical limitations do not prevent clinical use, including hypofractionation or stereotactic body radiation therapy.

Validation of a freehand 3D ultrasound system for morphological measures of the medial gastrocnemius muscle

Muscle volume and length are important parameters for examining the force-generating capabilities of muscle and their evaluation is necessary in studies that investigate muscle morphology and mechanical changes due to age, function, pathology, surgery and training. In this study, we assessed the validity and reliability of in vivo muscle volume and muscle belly length measurement using a multiple sweeps freehand 3D ultrasound (3DUS). The medial gastrocnemius of 10 subjects was scanned at three ankle joint angles (15°, 0° and −15° dorsiflexion) three times using the freehand 3DUS and once on the following day using magnetic resonance imaging (MRI). All freehand 3DUS and MRI images were segmented, volumes rendered and volumes and muscle belly lengths measured. The freehand 3DUS overestimated muscle volume by 1.9±9.1 mL, 1.1±3.8% difference and underestimated muscle belly length by 3.0±5.4 mm, 1.3±2.2% difference. The intra-class correlation coefficients (ICC) for repeated freehand 3DUS system measures of muscle volume and muscle belly length were greater than 0.99 and 0.98, respectively. The ICCs for the segmentation process reliability for the freehand 3DUS system and MRI for muscle volume were both greater than 0.99 and muscle belly length were 0.97 and 0.99, respectively. Freehand 3DUS is a valid and reliable method for the measurement of human muscle volume and muscle belly length in vivo. It could be used as an alternative to MRI for measuring in vivo muscle morphology and thus allowing the determination of PCSA and estimation of the force-generating capacity of individual muscles within the setting of a biomechanics laboratory.

Three-dimensional ultrasound reconstruction of the pelvicaliceal system: an in-vitro study

Three-dimensional (3D) reconstruction of the pelvicaliceal system (PCS) can be helpful for percutaneous renal procedures. 3D reconstruction of the PCS using ultrasound (US) has not been studied. We determined the feasibility and accuracy of 3DUS reconstruction of the PCS in an in vitro model. Ten pig kidneys were scanned in vitro using freehand 3DUS (Logiq 9, GE medical systems). Multi-planar reformatted (MPR) and volume rendered (VR) reconstructions of the PCS were processed on a workstation. Using resin casts of the PCS as the reference standard, MPR reconstructions were compared for maximal polar and antero-posterior (AP) PCS length, lower pole infundibular (LPInf) diameter and number of calices. VR movies were compared for number of calices. Three blinded reviewers matched VR movies to casts and given an "anatomical representation" score using a five-point scale. There were no significant differences in maximal AP length, LPInf diameter or number of calices between MPR reconstructions and casts. Maximal polar length between MPR reconstructions and casts were different (t = 6.44, P = 0.0001). VR movie reconstructions underestimated the number of calices visualised (t = 3.23, P = 0.01). A total of 22 out of 30 (73%) 3D VR videos were accurately matched to their casts. The 3D VR median score for anatomical representation was 3 (fair representation). Three-dimensional ultrasound reconstruction of the porcine PCS is quantitatively comparable to corresponding casts of the PCS. 3D VR movies of the PCS were a fair representation of the PCS anatomy. 3DUS is a potential tool in the planning and execution of percutaneous renal procedures.

3D reconstruction of the skeletal anatomy of the normal neonatal foot using 3D ultrasound

Currently imaging plays a limited role in the assessment of the neonate with a foot deformity. The aim of this study was to establish a technique for examining the neonatal foot with three-dimensional ultrasound (3D US). 3D US was attempted on the normal feet of 20 infants (9 male, 11 female) under 6 weeks old (range 35-41 days). The data sets were obtained whilst the infants were feeding or asleep to minimize movement artefact. A high-resolution optically tracked freehand 3D US system (Diasus, 16 MHz transducer) was used with Stradx software to acquire and analyse the data sets. Manual segmentation of the non-ossified tarsi from the data sets was performed. Five infants were too restless to be examined. 107 data sets were recorded from 22 feet of the remaining 15 infants. 21 of the data sets were discarded due to movement artefact. 86 were suitable for manual segmentation. Surface interpolation of the segmented data sets produced surface rendered reconstructions illustrating the complex 3D anatomy of the foot. This new technique may offer a method of examining the deformed foot, e.g. congenital talipes equinovarus.

Freehand three‐dimensional ultrasound in the diagnosis of fetal anomalies

Purpose: To determine the clinical impact and additional information of freehand three‐dimensional ultrasound (3DUS) in the diagnosis of fetal anomalies compared to two‐dimensional ultrasound (2DUS).Methods: We studied a total of 146 anomalies found in 95 fetuses. In all of them the fetal anomaly was first assessed by 2DUS, and then by freehand 3DUS. According to the fetal anomaly, fetal or maternal conditions, one or more of the following modes of data capture were employed: volume capture (n = 42 anomalies), static capture (n = 21 anomalies), and free style capture (n = 83 anomalies), then the most suitable screen presentation was used. Clinical impact, fetal outcome and additional information were determined in all cases.Results: Freehand 3DUS images provided additional information only in three anomalies (2%) compared with 2DUS, were equivalent in 132 anomalies (90%), and were disadvantageous in 11 anomalies (8%) In most cases, when the anomalies were well visualized by 2DUS, the 3DUS images added no further information. In none of the cases the 3DUS changed the clinical management. Furthermore, all files obtained by 3DUS were more advantageous in term of post‐processing capabilities, manipulation of images by multiples physician and teaching activities compared with 2DUS.Conclusions: The different freehand 3DUS modalities were diagnostic equivalent to 2DUS in the majorities of the clinical cases and has no additional clinical impact on patient management. The most important advantages were related to the post‐processing capabilities.

F73New modes of capture by freehand three‐dimensional ultrasound in the prenatal diagnosis of fetal anomalies

BackgroundThe aim of this study was to see the contribution of three different modes of capture of data by the freehand three‐dimensional ultrasound (3D US) in the prenatal diagnosis of fetal anomalies.MethodWe studied a total of 34 pregnant women. In all of them a fetal anomaly was previously assessed by 2D US. Planar US probes and a 3D software (3D‐ViewTM) were used on a digital Gaia 8800 scanner. Three modes of data capture were employed: volume capture (to capture a volume), static capture (to capture motion; a combination of B‐mode and M‐mode), and free style capture (to capture a big region of interest; ROI), then the most suitable screen presentation was used according to the mode of capture.ResultsWe found a total of 41 anomalies on 34 fetuses which are: Heart (17), abdomen (8), central nervous system (6) and miscellaneous (10). We were able to see all anomalies previously detected by 2D US. By using volume capture and rendering image we were able to detect also anomalies of fingers and face, no previously detected by 2D. However volume capture was the most difficult mode to perform. Static capture was the most suitable to study fetal heart malformations (as A‐V canal) and arrhythmias. Free style capture give us a B‐mode digital video of the ROI (hydrocephalus, spina bifida, gastroschisis, omphalocele, adominal cysts, kidney malformations). Good pictures by using the last two modes of capture were easy to obtain. We also benefit of all the advantages of using digital technology, like to have the information as a virtual patient.ConclusionThe appropriate use of different modes of capture of data by free hand 3D US in combination with 2D US gives a new perspective of using this new technology in the diagnosis of fetal anomalies.