Fast surface and volume estimation from non-parallel cross-sections, for freehand three-dimensional ultrasound

Longitudinal trajectory of medial gastrocnemius muscle growth in the first years of life

AIM

To define the longitudinal trajectory of gastrocnemius muscle growth in 6- to 36-month-old children with and without spastic cerebral palsy (SCP) and to compare trajectories by levels of gross motor function (Gross Motor Function Classification System, GMFCS) and presumed brain-lesion timing.

METHOD

Twenty typically developing children and 24 children with SCP (GMFCS levels I-II/III-IV = 15/9), were included (28/16 females/males; mean age at first scan 15.4 months [standard deviation 4.93, range 6.24-23.8]). Three-dimensional freehand ultrasound was used to repeatedly assess muscle volume, length, and cross-sectional area (CSA), resulting in 138 assessments (mean interval 7.9 months). Brain lesion timing was evaluated with magnetic resonance imaging classification. Linear mixed-effects models defined growth rates, adjusted for GMFCS levels and presumed brain-lesion timing.

RESULTS

At age 12 months, children with SCP showed smaller morphological muscle size than typically developing children (5.8 mL vs 9.8 mL, p < 0.001), while subsequently no differences in muscle growth were found between children with and without SCP (muscle volume: 0.65 mL/month vs 0.74 mL/month). However, muscle volume and CSA growth rates were lower in children classified in GMFCS levels III and IV than typically developing children and those classified in GMFCS levels I and II, with differences ranging from -56% to -70% (p < 0.001).

INTERPRETATION

Muscle growth is already hampered during infancy in SCP. Muscle size growth further reduces with decreasing functional levels, independently from the brain lesion. Early monitoring of muscle growth combined with early intervention is needed.

Reliability and validity of assessing lower-limb muscle architecture of patients with cerebral palsy (CP) using ultrasound: A systematic review

AIMS

To investigate the reliability, validity, and level of evidence of applying ultrasound in assessing the lower-limb muscles of patients with cerebral palsy (CP).

METHOD

Publications in Medline, PubMed, Web of Science, and Embase were searched on May 10, 2023, to identify and examine relevant studies investigating the reliability/validity of ultrasound in evaluating the architecture of CP lower-limb muscles systematically, following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis 2020 guidelines.

RESULTS

Out of 897 records, 9 publications with 111 CP participants aged 3.8-17.0 years were included (8 focused on intra-rater and inter-rater reliability, 2 focused on validity, and 4 were with high quality). The ultrasound-based measurements of muscle thickness (intra-rater only), muscle length, cross-sectional area, muscle volume, fascicle length, and pennation angle showed high reliability, with the majority of intraclass correlation coefficient (ICC) values being larger than 0.9. Moderate-to-good correlations between ultrasound and magnetic resonance imaging measurements existed in muscle thickness and cross-sectional area (0.62 ≤ ICC ≤ 0.82).

INTERPRETATION

Generally, ultrasound has high reliability and validity in evaluating the CP muscle architecture, but this is mainly supported by moderate and limited levels of evidence. More high-quality future studies are needed.

Morphological Medial Gastrocnemius Muscle Growth in Ambulant Children with Spastic Cerebral Palsy: A Prospective Longitudinal Study

Only cross-sectional studies have demonstrated muscle deficits in children with spastic cerebral palsy (SCP). The impact of gross motor functional limitations on altered muscle growth remains unclear. This prospective longitudinal study modelled morphological muscle growth in 87 children with SCP (age range 6 months to 11 years, Gross Motor Function Classification System [GMFCS] level I/II/III = 47/22/18). Ultrasound assessments were performed during 2-year follow-up and repeated for a minimal interval of 6 months. Three-dimensional freehand ultrasound was applied to assess medial gastrocnemius muscle volume (MV), mid-belly cross-sectional area (CSA) and muscle belly length (ML). Non-linear mixed models compared trajectories of (normalized) muscle growth between GMFCS-I and GMFCS-II&III. MV and CSA growth trajectories showed a piecewise model with two breakpoints, with the highest growth before 2 years and negative growth rates after 6-9 years. Before 2 years, children with GMFCS-II&III already showed lower growth rates compared to GMFCS-I. From 2 to 9 years, the growth rates did not differ between GMFCS levels. After 9 years, a more pronounced reduction in normalized CSA was observed in GMFCS-II&III. Different trajectories in ML growth were shown between the GMFCS level subgroups. These longitudinal trajectories highlight monitoring of SCP muscle pathology from early ages and related to motor mobility. Treatment planning and goals should stimulate muscle growth.

Progressive resistance training for children with cerebral palsy: A randomized controlled trial evaluating the effects on muscle strength and morphology

Children with spastic cerebral palsy often present with muscle weakness, resulting from neural impairments and muscular alterations. While progressive resistance training (PRT) improves muscle weakness, the effects on muscle morphology remain inconclusive. This investigation evaluated the effects of a PRT program on lower limb muscle strength, morphology and gross motor function. Forty-nine children with spastic cerebral palsy were randomized by minimization. The intervention group (nparticipants = 26, age: 8.3 ± 2.0 years, Gross Motor Function Classification System [GMFCS] level I/II/III: 17/5/4, nlegs = 41) received a 12-week PRT program, consisting of 3-4 sessions per week, with exercises performed in 3 sets of 10 repetitions, aiming at 60%–80% of the 1-repetition maximum. Training sessions were performed under supervision with the physiotherapist and at home. The control group (nparticipants = 22, age: 8.5 ± 2.1 year, GMFCS level I/II/III: 14/5/3, nlegs = 36) continued usual care including regular physiotherapy and use of orthotics. We assessed pre- and post-training knee extension, knee flexion and plantar flexion isometric strength, rectus femoris, semitendinosus and medial gastrocnemius muscle morphology, as well as functional strength, gross motor function and walking capacity. Data processing was performed blinded. Linear mixed models were applied to evaluate the difference in evolution over time between the control and intervention group (interaction-effect) and within each group (time-effect). The α-level was set at p = 0.01. Knee flexion strength and unilateral heel raises showed a significant interaction-effect (p ≤ 0.008), with improvements in the intervention group (p ≤ 0.001). Moreover, significant time-effects were seen for knee extension and plantar flexion isometric strength, rectus femoris and medial gastrocnemius MV, sit-to-stand and lateral step-up in the intervention group (p ≤ 0.004). Echo-intensity, muscle lengths and gross motor function showed limited to no changes. PRT improved strength and MV in the intervention group, whereby strength parameters significantly or close to significantly differed from the control group. Although, relative improvements in strength were larger than improvements in MV, important effects were seen on the maintenance of muscle size relative to skeletal growth. In conclusion, this study proved the effectiveness of a home-based, physiotherapy supervised, PRT program to improve isometric and functional muscle strength in children with SCP without negative effects on muscle properties or any serious adverse events.

Clinical Trial Registration: ClinicalTrials.gov, identifier NCT03863197.

The Short-Term Impact of Botulinum Neurotoxin-A on Muscle Morphology and Gait in Children with Spastic Cerebral Palsy

Children with spastic cerebral palsy (SCP) are often treated with intramuscular Botulinum Neurotoxin type-A (BoNT-A). Recent studies demonstrated BoNT-A-induced muscle atrophy and variable effects on gait pathology. This group-matched controlled study in children with SCP compared changes in muscle morphology 8-10 weeks post-BoNT-A treatment (n = 25, median age 6.4 years, GMFCS level I/II/III (14/9/2)) to morphological changes of an untreated control group (n = 20, median age 7.6 years, GMFCS level I/II/III (14/5/1)). Additionally, the effects on gait and spasticity were assessed in all treated children and a subgroup (n = 14), respectively. BoNT-A treatment was applied following an established integrated approach. Gastrocnemius and semitendinosus volume and echogenicity intensity were assessed by 3D-freehand ultrasound, spasticity was quantified through electromyography during passive muscle stretches at different velocities. Ankle and knee kinematics were evaluated by 3D-gait analysis. Medial gastrocnemius (p = 0.018, -5.2%) and semitendinosus muscle volume (p = 0.030, -16.2%) reduced post-BoNT-A, but not in the untreated control group, while echogenicity intensity did not change. Spasticity reduced and ankle gait kinematics significantly improved, combined with limited effects on knee kinematics. This study demonstrated that BoNT-A reduces spasticity and partly improves pathological gait but reduces muscle volume 8-10 weeks post-injections. Close post-BoNT-A follow-up and well-considered treatment selection is advised before BoNT-A application in SCP.

Dynamic 3D Ultrasound Imaging of the Tibialis Anterior Muscle

Skeletal muscle volume has been mainly investigated under static conditions, i.e. isometric contractions. The aim of our study is to use ultrasound imaging to determine muscle deformation during movement. We used a custom-designed scanning rig to obtain 3D ultrasound images of a subject moving the foot from plantarflexion to dorsiflexion at constant velocity. Using motion capture, we computed the respective angle of the ankle for each frame and collected them in bins based on the measured angle (rounded on the next normal number). For each degree, we used Stradwin for the 3D reconstruction of the respective volume. We found increasing cross-sectional areas for increasing dorsiflexion angles. The proposed method is a promising approach for determining muscle volume during movement. Future studies aim at collecting more data to compute muscle volume and length during contraction and compare the results to isometric measurements.

Reduced Cross-Sectional Muscle Growth Six Months after Botulinum Toxin Type-A Injection in Children with Spastic Cerebral Palsy

Botulinum Neurotoxin type-A (BoNT-A) injections are widely used as first-line spasticity treatment in spastic cerebral palsy (SCP). Despite improved clinical outcomes, concerns regarding harmful effects on muscle morphology have been raised. Yet, the risk of initiating BoNT-A to reduce muscle growth remains unclear. This study investigated medial gastrocnemius (MG) morphological muscle growth in children with SCP (n = 26, median age of 5.2 years (3.5)), assessed by 3D-freehand ultrasound prior to and six months post-BoNT-A injections. Post-BoNT-A MG muscle growth of BoNT-A naive children (n = 11) was compared to (a) muscle growth of children who remained BoNT-A naive after six months (n = 11) and (b) post-BoNT-A follow-up data of children with a history of BoNT-A treatment (n = 15). Six months after initiating BoNT-A injection, 17% decrease in mid-belly cross-sectional area normalized to skeletal growth and 5% increase in echo-intensity were illustrated. These muscle outcomes were only significantly altered when compared with children who remained BoNT-A naive (+4% and -3%, respectively, p < 0.01). Muscle length growth persevered over time. This study showed reduced cross-sectional growth post-BoNT-A treatment suggesting that re-injections should be postponed at least beyond six months. Future research should extend follow-up periods investigating muscle recovery in the long-term and should include microscopic analysis.

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 Distal Hamstring Tendon Length and Cross-sectional Area Using 3-D Freehand Ultrasound

The objective of this study was to investigate the reliability of distal hamstring tendon morphology using freehand 3-D ultrasound (US). Freehand 3-D US scans were acquired for 16 young males and females, in two sessions, spaced a week apart. The length, volume, cross-sectional area (CSA) and echo intensity (EI) of the semitendinosus (ST), biceps femoris long and short head and semimembranosus (SM) tendons were acquired. Measurements of the CSA and EI were obtained from three sites along each tendon. The intra-class correlation coefficients ranged from 0.88-0.99 of the examined variables, indicating high test-retest reliability. In addition, the minimal detectable change (MDC) ranged from 0.255-3.766 mm (MDC% of the mean: 0.406%-12.558%) for hamstring tendon length, from 0.036-0.077 mL (MDC%: 1.548%-3.178%) for tendon volume, from 0.512-1.948 mm² (MDC%: 0.702%-3.586%) for CSA and from 0.898-2.586 au (MDC%: 1.145%-3.325%) for EI. Of the four hamstring tendons, ST had the greatest length (141.587 ± 10.701 mm) and EI (94.637 ± 5.536 au), while SM had the greatest volume (3.056 ± 0.421 mL) and CSA (115.277 ± 16.442 mm²) relative to other tendons. Freehand 3-D US appears to be a reliable tool for the evaluation of hamstring distal tendon morphology; hence, its use for in vivo evaluation of tendon properties is promising.

Cross-Sectional Area Measurement Techniques of Soft Tissue: A Literature Review

Evaluation of the biomechanical properties of soft tissues by measuring the stress-strain relationships has been the focus of numerous investigations. The accuracy of stress depends, in part, upon the determination of the cross-sectional area (CSA). However, the complex geometry and pliability of soft tissues, especially ligaments and tendons, make it difficult to obtain accurate CSA, and the development of CSA measurement methods of soft tissues continues. Early attempts to determine the CSA of soft tissues include gravimetric method, geometric approximation technique, area micrometer method, and microtomy technique. Since 1990, a series of new methods have emerged, including medical imaging techniques (e.g. magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging (USI)), laser techniques (e.g. the laser micrometer method, the linear laser scanner (LLS) technique, and the laser reflection system (LRS) method), molding techniques, and three-dimensional (3D) scanning techniques.

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 in vivo 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 8 years 4 months ± 1 year 10 months, 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 < 0.3 mL (1%) and underestimated SOL by < 1.3 mL (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 < 4.0 mL (14%) and 3.2 mL (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 in vivo. 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.

Muscle Architecture Assessment: Strengths, Shortcomings and New Frontiers of in Vivo Imaging Techniques

Skeletal muscle structural assembly (and its remodeling in response to loading-unloading states) can be investigated macroscopically by assessing muscle architecture, described as fascicle geometric disposition within the muscle. Over recent decades, various medical imaging techniques have been developed to facilitate the in vivo assessment of muscle architecture. However, the main advantages and limitations of these methodologies have been fragmentally discussed. In the present article, the main techniques used for the evaluation of muscle architecture are presented: conventional B-mode ultrasonography, extended-field-of-view ultrasound, 3-D ultrasound and magnetic resonance imaging-based diffusion tensor imaging. By critically discussing potentials and shortcomings of each methodology, we aim to provide readers with an overview of both established and new techniques for the in vivo assessment of muscle architecture. This review may serve as decision guidance facilitating selection of the appropriate technique to be applied in biomedical research or clinical routine.

Freehand 3-D Ultrasound Imaging: A Systematic Review

Two-dimensional ultrasound (US) imaging has been successfully used in clinical applications as a low-cost, portable and non-invasive image modality for more than three decades. Recent advances in computer science and technology illustrate the promise of the 3-D US modality as a medical imaging technique that is comparable to other prevalent modalities and that overcomes certain drawbacks of 2-D US. This systematic review covers freehand 3-D US imaging between 1970 and 2017, highlighting the current trends in research fields, the research methods, the main limitations, the leading researchers, standard assessment criteria and clinical applications. Freehand 3-D US systems are more prevalent in the academic environment, whereas in clinical applications and industrial research, most studies have focused on 3-D US transducers and improvement of hardware performance. This topic is still an interesting active area for researchers, and there remain many unsolved problems to be addressed.

The tendinopathic Achilles tendon does not remain iso-volumetric upon repeated loading: insights from 3D ultrasound

Mid-portion Achilles tendinopathy (MAT) alters the normal three-dimensional (3D) morphology of the Achilles tendon (AT) at rest and under a single tensile load. However, how MAT changes the 3D morphology of AT during repeated loading remains unclear. This study compared the AT longitudinal, transverse and volume strains during repeated loading in MAT with those of the contralateral tendon in people with unilateral MAT. Ten adults with unilateral MAT performed 10 successive 25 second submaximal (50%) voluntary isometric plantarflexion contractions with both legs. Freehand 3D ultrasound scans were recorded and used to measure whole AT, free AT, and proximal AT longitudinal strains and free AT cross-sectional area (CSA) and volume strains. The free AT experienced higher longitudinal and CSA strain and reached steady state following a greater number of contractions (5 contractions) in MAT compared to the contralateral tendon (3 contractions). Further, free tendon CSA and volume strained more in MAT than contralateral tendon from the first contraction, whereas free AT longitudinal strain was not greater than the contralateral tendon until the fourth contraction. Volume loss from the tendon core therefore preceded the greater longitudinal strain in MAT. Overall, these findings suggest that the tendinopathic free AT experiences an exaggerated longitudinal and transverse strain response under repeated loading that is underpinned by an altered interaction between solid and fluid tendon matrix components. These alterations are indicative of accentuated poroelasticity and an altered local stress-strain environment within the tendinopathic free tendon matrix, which could affect tendon remodelling via mechanobiological pathways.

Three-dimensional geometrical changes of the human tibialis anterior muscle and its central aponeurosis measured with three-dimensional ultrasound during isometric contractions

Background. Muscles not only shorten during contraction to perform mechanical work, but they also bulge radially because of the isovolumetric constraint on muscle fibres. Muscle bulging may have important implications for muscle performance, however quantifying three-dimensional (3D) muscle shape changes in human muscle is problematic because of difficulties with sustaining contractions for the duration of an in vivo scan. Although two-dimensional ultrasound imaging is useful for measuring local muscle deformations, assumptions must be made about global muscle shape changes, which could lead to errors in fully understanding the mechanical behaviour of muscle and its surrounding connective tissues, such as aponeurosis. Therefore, the aims of this investigation were (a) to determine the intra-session reliability of a novel 3D ultrasound (3DUS) imaging method for measuring in vivo human muscle and aponeurosis deformations and (b) to examine how contraction intensity influences in vivo human muscle and aponeurosis strains during isometric contractions.

Methods. Participants (n = 12) were seated in a reclined position with their left knee extended and ankle at 90° and performed isometric dorsiflexion contractions up to 50% of maximal voluntary contraction. 3DUS scans of the tibialis anterior (TA) muscle belly were performed during the contractions and at rest to assess muscle volume, muscle length, muscle cross-sectional area, muscle thickness and width, fascicle length and pennation angle, and central aponeurosis width and length. The 3DUS scan involved synchronous B-mode ultrasound imaging and 3D motion capture of the position and orientation of the ultrasound transducer, while successive cross-sectional slices were captured by sweeping the transducer along the muscle.

Results. 3DUS was shown to be highly reliable across measures of muscle volume, muscle length, fascicle length and central aponeurosis length (ICC ≥ 0.98, CV < 1%). The TA remained isovolumetric across contraction conditions and progressively shortened along its line of action as contraction intensity increased. This caused the muscle to bulge centrally, predominantly in thickness, while muscle fascicles shortened and pennation angle increased as a function of contraction intensity. This resulted in central aponeurosis strains in both the transverse and longitudinal directions increasing with contraction intensity.

Discussion. 3DUS is a reliable and viable method for quantifying multidirectional muscle and aponeurosis strains during isometric contractions within the same session. Contracting muscle fibres do work in directions along and orthogonal to the muscle’s line of action and central aponeurosis length and width appear to be a function of muscle fascicle shortening and transverse expansion of the muscle fibres, which is dependent on contraction intensity. How factors other than muscle force change the elastic mechanical behaviour of the aponeurosis requires further investigation.

Cancer multicellular spheroids: volume assessment from a single 2D projection

Volume is one of the most important features for the characterization of a tumour on a macroscopic scale. It is often used to assess the effectiveness of care treatments, thus making its correct evaluation a crucial issue for patient care. Similarly, volume is a key feature on a microscopic scale. Multicellular cancer spheroids are 3D tumour models widely employed in pre-clinical studies to test the effects of drugs and radiotherapy treatments. Very few methods have been proposed to estimate the tumour volume arising from a 2D projection of multicellular spheroids, and even fewer have been designed to provide a 3D reconstruction of the tumour shape. In this work, we propose Reconstruction and Visualization from a Single Projection (ReViSP), an automatic method conceived to reconstruct the 3D surface and estimate the volume of single cancer multicellular spheroids, or even of spheroid cultures. As the input parameter ReViSP requires only one 2D projection, which could be a widefield microscope image. We assessed the effectiveness of our method by comparing it with other approaches. To this purpose, we used a new strategy that allowed us to achieve accurate volume measurements based on the analysis of home-made 3D objects, built by mimicking the spheroid morphology. The results confirmed the effectiveness of our method for both 3D reconstruction and volume assessment. ReViSP software is distributed as an open source tool.

A novel breast ultrasound system for providing coronal images: system development and feasibility study

Breast ultrasound images along coronal plane contain important diagnosis information. However, conventional clinical 2D ultrasound cannot provide such images. In order to solve this problem, we developed a novel ultrasound system aimed at providing breast coronal images. In this system, a spatial sensor was fixed on an ultrasound probe to obtain the image spatial data. A narrow-band rendering method was used to form coronal images based on B-mode images and their corresponding spatial data. Software was developed for data acquisition, processing, rendering and visualization. In phantom experiments, 20 inclusions with different size (5-20 mm) were measured using this new system. The results obtained by the new method well correlated with those measured by a micrometer (y=1.0147x, R(2)=0.9927). The phantom tests also showed that this system had excellent intra- and inter-operator repeatability (ICC>0.995). Three subjects with breast lesions were scanned in vivo using this new system and a commercially available three-dimensional (3D) probe. The average scanning times for the two systems were 64 s and 74 s, respectively. The results revealed that this new method required shorter scanning time. The tumor sizes measured on the coronal plane provided by the new method were smaller by 5.6-11.9% in comparison with the results of the 3D probe. The phantom tests and preliminary subject tests indicated the feasibility of this system for clinical applications by providing additional information for clinical breast ultrasound diagnosis.

Three-dimensional deformation and transverse rotation of the human free Achilles tendon in vivo during isometric plantarflexion contraction

Freehand three-dimensional ultrasound (3DUS) was used to investigate longitudinal and biaxial transverse deformation and rotation of the free Achilles tendon in vivo during a voluntary submaximal isometric muscle contraction. Participants ( n = 8) were scanned at rest and during a 70% maximal voluntary isometric contraction (MVIC) of the plantarflexors. Ultrasound images were manually digitized to render a 3D reconstruction of the free Achilles tendon for the computation of tendon length, volume, cross-sectional area (CSA), mediolateral diameter (MLD), anteroposterior diameter (APD), and transverse rotation. Tendon longitudinal and transverse (CSA, APD, and MLD) deformation and strain at 70% MVIC were calculated relative to the resting condition. There was a significant main effect of contraction on tendon length and mean CSA, MLD, and APD ( P < 0.05), but no effect on tendon volume ( P = 0.70). Group mean transverse strains for CSA, MLD, and APD averaged over the length of the tendon were −5.5%, −8.7% and 8.7%, respectively. Peak CSA, MLD, and APD transverse strains all occurred between 40% and 60% of tendon length. Transverse rotation of the free tendon was negligible at rest but increased under load, becoming externally rotated relative to the calcaneal insertion. The relationship between longitudinal and transverse strains of the free Achilles tendon during muscle-induced elongation may be indicative of interfascicle reorganization. The finding that transverse rotation and strain peaked in midportion of the free Achilles tendon may have important implications for tendon injury mechanisms and estimation of tendon stress in vivo.

In vivo measurement of human achilles tendon morphology using freehand 3-D ultrasound

This study investigated the accuracy of phantom volume and length measurements and the reliability of in vivo Achilles tendon (AT) volume, length and cross-sectional area measurements obtained using freehand 3-D ultrasound. Participants (n = 13) were scanned on consecutive days under active and passive loading conditions. In vivo AT length was evaluated using a two-point method and an approach that accounted for AT curvature (centroid method). Three-dimensional ultrasound provided accurate measures of phantom volume and length (mean difference = 0.05 mL and 0.2 mm, respectively) and reliable in vivo measures of AT volume, length and average cross-sectional area, with all intra-class correlations coefficients greater than 0.98. The mean minimally detectable changes for in vivo AT volume, two-point length and centroid length were 0.2 mL, 1.5 mm and 2.0 mm, respectively. Two-point AT length underestimated centroid AT length by 0.7 mm, suggesting that the effect of curvature on in vivo AT length is negligible.

Trabecular bone structure correlates with hand posture and use in hominoids

Bone is capable of adapting during life in response to stress. Therefore, variation in locomotor and manipulative behaviours across extant hominoids may be reflected in differences in trabecular bone structure. The hand is a promising region for trabecular analysis, as it is the direct contact between the individual and the environment and joint positions at peak loading vary amongst extant hominoids. Building upon traditional volume of interest-based analyses, we apply a whole-epiphysis analytical approach using high-resolution microtomographic scans of the hominoid third metacarpal to investigate whether trabecular structure reflects differences in hand posture and loading in knuckle-walking (Gorilla, Pan), suspensory (Pongo, Hylobates and Symphalangus) and manipulative (Homo) taxa. Additionally, a comparative phylogenetic method was used to analyse rates of evolutionary changes in trabecular parameters. Results demonstrate that trabecular bone volume distribution and regions of greatest stiffness (i.e., Young's modulus) correspond with predicted loading of the hand in each behavioural category. In suspensory and manipulative taxa, regions of high bone volume and greatest stiffness are concentrated on the palmar or distopalmar regions of the metacarpal head, whereas knuckle-walking taxa show greater bone volume and stiffness throughout the head, and particularly in the dorsal region; patterns that correspond with the highest predicted joint reaction forces. Trabecular structure in knuckle-walking taxa is characterised by high bone volume fraction and a high degree of anisotropy in contrast to the suspensory brachiators. Humans, in which the hand is used primarily for manipulation, have a low bone volume fraction and a variable degree of anisotropy. Finally, when trabecular parameters are mapped onto a molecular-based phylogeny, we show that the rates of change in trabecular structure vary across the hominoid clade. Our results support a link between inferred behaviour and trabecular structure in extant hominoids that can be informative for reconstructing behaviour in fossil primates.

Three-dimensional ultrasound imaging

This review is about the development of three-dimensional (3D) ultrasonic medical imaging, how it works, and where its future lies. It assumes knowledge of two-dimensional (2D) ultrasound, which is covered elsewhere in this issue. The three main ways in which 3D ultrasound may be acquired are described: the mechanically swept 3D probe, the 2D transducer array that can acquire intrinsically 3D data, and the freehand 3D ultrasound. This provides an appreciation of the constraints implicit in each of these approaches together with their strengths and weaknesses. Then some of the techniques that are used for processing the 3D data and the way this can lead to information of clinical value are discussed. A table is provided to show the range of clinical applications reported in the literature. Finally, the discussion relating to the technology and its clinical applications to explain why 3D ultrasound has been relatively slow to be adopted in routine clinics is drawn together and the issues that will govern its development in the future explored.

Effect of tibial drill angles on bone tunnel aperture during anterior cruciate ligament reconstruction

BACKGROUND

Anatomic reconstruction of the anterior cruciate ligament has received greater attention as patient outcome assessment has become increasingly sophisticated. A goal during anatomic reconstruction should be the creation of a tibial tunnel aperture that is similar in size and orientation to the native anterior cruciate ligament insertion. Aperture morphology depends primarily on three factors: (1) drill-bit diameter, (2) the angle at which the tunnel intersects the tibial plateau (drill-guide angle), and (3) the tibial tunnel orientation in the transverse plane (transverse drill angle). We evaluated the influence of the aforementioned factors on tibial bone-tunnel aperture size and orientation.

METHODS

With use of various drill-bit diameters at different drill-guide angles, tunnel aperture areas were calculated on the basis of an elliptical shape. The change in tunnel aperture orientation within the transverse plane (along the tibial plateau surface) was quantified by calculating the change in anteroposterior and mediolateral lengths of the aperture.

RESULTS

Use of a 9-mm drill-bit at a 45 degrees drill-guide angle created a 90-mm(2) bone-tunnel aperture area. Decreasing the drill-guide angle from 65 degrees to 30 degrees resulted in an increase in area of 81%. An aperture oriented 45 degrees relative to the orientation of the native insertion of the anterior cruciate ligament in the transverse plane fell short of the anatomic anteroposterior distance by 2.3 mm and exceeded the mediolateral distance by 1.4 mm on the basis of a 9-mm drill-bit at a drill-guide angle of 45 degrees.

CONCLUSIONS

During anterior cruciate ligament reconstruction, the drill-bit diameter, sagittal drill angle, and transverse drill angle can all affect tibial tunnel aperture size and orientation. An improperly sized and oriented tunnel aperture may increase the risk of damaging surrounding structures. An optimal combination of these parameters should be chosen during anatomic reconstruction of the anterior cruciate ligament.

A new adaptive interpolation algorithm for 3D ultrasound imaging with speckle reduction and edge preservation

Conventional interpolation algorithms for reconstructing freehand three-dimensional (3D) ultrasound data always contain speckle noises and artifacts. This paper describes a new algorithm for reconstructing regular voxel arrays with reduced speckles and preserved edges. To study speckle statistics properties including mean and variance in sequential B-mode images in 3D space, experiments were conducted on an ultrasound resolution phantom and real human tissues. In the volume reconstruction, the homogeneity of the neighborhood for each voxel was evaluated according to the local variance/mean of neighboring pixels. If a voxel was locating in a homogeneous region, its neighboring pixels were averaged as the interpolation output. Otherwise, the size of the voxel neighborhood was contracted and the ratio was re-calculated. If its neighborhood was deemed as an inhomogeneous region, the voxel value was calculated using an adaptive Gaussian distance weighted method with respect to the local statistics. A novel method was proposed to reconstruct volume data set with economical usage of memory. Preliminary results obtained from the phantom and a subject's forearm demonstrated that the proposed algorithm was able to well suppress speckles and preserve edges in 3D images. We expect that this study can provide a useful imaging tool for clinical applications using 3D ultrasound.

A morphology-based approach for interslice interpolation of anatomical slices from volumetric images

This paper proposes a new morphology-based approach for the interslice interpolation of current transformer (CT) and MRI datasets composed of parallel slices. Our approach is object based and accepts as input data binary slices belonging to the same anatomical structure. Such slices may contain one or more regions, since topological changes between two adjacent slices may occur. Our approach handles explicitly interslice topology changes by decomposing a many-to-many correspondence into three fundamental cases: one-to-one, one-to-many, and zero-to-one correspondences. The proposed interpolation process is iterative. One iteration of this process computes a transition sequence between a pair of corresponding input slices, and selects the element located at equal distance from the input slices. This algorithmic design yields a gradual, smooth change of shape between the input slices. Therefore, the main contribution of our approach is its ability to interpolate between two anatomic shapes by creating a smooth, gradual change of shape, and without generating over-smoothed interpolated shapes.

Morphometrical study of plant vacuolar dynamics in single cells using three-dimensional reconstruction from optical sections

In higher plants, vacuoles increase their volumes in accordance with cell enlargement and occupy most of the cell volume. However, quantitative analyses of vacuolar contributions during changes in cell morphology have been hampered by the inadequacies and frequent artifacts associated with current three-dimensional (3-D) reconstruction methods of images derived from light microscopy. To overcome the limitations of quantifying 3-D structures, we have introduced 3-D morphometrics into light microscopy, adopting a contour-based approach for which we have developed an interpolation method. Using this software, named REANT, the morphological and morphometrical changes in protoplasts and vacuoles during plasmolysis could be investigated. We employed the tobacco (Nicotiana tabacum) BY-2 cell line No.7, expressing a GFP-AtVam3p fusion protein, BY-GV7, using GFP as a marker of vacuolar membranes (VMs). By vital staining of the plasma membrane (PM) of cells, we simultaneously obtained optical sections of both the PM and VM. We, therefore, reconstructed the 3-D structures of protoplasts and vacuoles before and after plasmolysis. We were able to identify the appearance of elliptical structures of VMs in the vacuolar lumen, and to determine that they were derived from cytoplasmic strands. From the 3-D structures, the volumes and surface areas were measured at the single cell level. The shrinkage of vacuoles accounted for most of the decrease in protoplast volume, while the surface area of the vacuoles remained mostly unchanged. These morphometrical analyses suggest that the elliptical structures are reservoirs for excess VMs that result from the response to rapid decreases in vacuolar and protoplast volumes.

Processing and visualizing three-dimensional ultrasound data

This paper describes techniques for the visualization and processing of three-dimensional (3D) ultrasound data. The nature of such data demands specialized algorithms, which differ from those employed for other medical imaging modalities. In this paper, the emphasis is placed on generic processing techniques, which are relevant across a wide range of 3D ultrasound application domains.

Surface extraction with a three-dimensional freehand ultrasound system

This paper presents a system for acquiring three-dimensional ultrasound data and extracting surfaces of the examined structures. The acquisition is performed freehand with a PC-based two dimensional ultrasound machine and an optical tracker. The extraction of surfaces from ultrasound data are normally inhibited by speckle, shadowing and gaps in the acquired data. A new method is developed that extracts a surface directly from the irregularly spaced, noisy freehand ultrasound data. The freehand data are first interpolated with radial basis functions and then a mesh is formed along an isosurface of the functional interpolation. The ability of radial basis functions to smooth speckle and interpolate across gaps is demonstrated on a series of experiments with phantoms and human tissue in a water bath. The geometry of the extracted surface matches the external measurements with an average difference ranging from 0.8 to 2.9 mm. These differences are within the range of errors from calibration, resolution and landmark localization. The experiments also show the ability to create continuous and realistic surfaces from scans that require multiple sweeps over a structure.

Two- and three-dimensional ultrasound in the development of a needle-free injection system

Ultrasound was used to assess a needle-free injection device for both intradermal and subcutaneous injections. The aim of this study was, first, to differentiate intradermal from subcutaneous injections, both in vivo and in vitro using 2D ultrasound, and second, to quantify the amount of injectate that actually arrives within the dermis or subcutaneous tissues using volume measurements derived from high-resolution 3D ultrasound data sets, using a freehand system (Stradx), developed by the Cambridge University Departments of Engineering and Radiology. For the in vitro study the devices were filled with dye and injected into a pig preparation. The injection site was examined with high-resolution ultrasound and subsequently dissected to locate the injected dye with respect to the dermis. For the in vivo study, 8 volunteers received needle-free injections of normal saline. High-resolution 2D images and 3D data sets were obtained of the injected sites. Proprioceptive information for the 3D data sets was produced using an optically tracked freehand system. Segmentation of the 3D data sets gave an estimation of the volume of injected material (injectate) within the dermis. The results demonstrated that 2D ultrasound could identify the location of the injectate in the in vitro experiments and successfully distinguished an intradermal from a subcutaneous injection. In the in vivo study, 2D ultrasound clearly demonstrated the injectate location within the volunteers' dermis but was less able to demonstrate the dispersion of injectate within the subcutaneous tissues.

High-definition freehand 3-D ultrasound

This paper describes a high-definition freehand 3-D ultrasound (US) system, with accuracy surpassing that of previously documented systems. 3-D point location accuracy within a US data set can be achieved to within 0.5 mm. Such accuracy is possible through a series of novel system-design and calibration techniques. The accuracy is quantified using a purpose-built tissue-mimicking phantom, designed to create realistic clinical conditions without compromising the accuracy of the measurement procedure. The paper includes a thorough discussion of the various ways of measuring system accuracy and their relative merits; and compares, in this context, all recently documented freehand 3-D US systems.

Sensorless freehand 3-D ultrasound using regression of the echo intensity

In freehand 3-D ultrasound (US), a position sensor is attached to the probe of a 2-D US machine. The resulting 3-D data permit flexible visualisation and more accurate volume measurement than can be achieved using 2-D B-scans alone; however, the use of the position sensor can be inconvenient for the clinician. The objective is, thus, to replace the sensor with a technique for estimating the probe trajectory based on the B-scan images, themselves. One such technique exists, based on decorrelation algorithms. This paper presents an alternative approach based on linear regression of the echo-envelope intensity signal. A probabilistic analysis of the speckle characteristics of the US signal leads to a linear model, on which the regression algorithm is based. The gradient parameter of this model is shown to be directly related to probe motion. The viability of the new approach is demonstrated through simulations and in vitro and in vivo experiments.

A multiscale algorithm for three-dimensional free-hand ultrasound

This paper presents a multiscale algorithm for the reconstruction of human anatomy from a set of ultrasound (US) images. Reconstruction is formulated in a Bayesian framework as an optimization problem with a large number of unknown variables. Human tissues are represented by the interpolation of coefficients associated to the nodes of a 3-D cubic grid. The convergence of the Bayesian method is usually slow and initialization dependent. In this paper, a multiscale approach is proposed to increase the convergence rate of the iterative process of volume estimation. A coarse estimate of the volume is first obtained using a cubic grid with a small number of nodes initialized with a constant value computed from the observed data. The volume estimate is then recursively improved by refining the grid step. Experimental results are provided to show that multiscale method achieves faster convergence rates compared with a single-scale approach. This is the key improvement toward real-time implementations. Experimental results of 3-D reconstruction of human anatomy are presented to assess the performance of the algorithm and comparisons with the single-scale method are presented.

Freehand 3D ultrasound without voxels: volume measurement and visualisation using the Stradx system

This paper describes recent developments in the Stradx freehand 3D ultrasound system. Unlike other systems, Stradx works directly from the raw B-scans and their relative positions, without first resampling this unstructured data onto a regular voxel array. The paper discusses the many advantages of this unique approach, and presents new developments in the visualisation and quantitative analysis of freehand 3D ultrasound data, including novel volume rendering schemes and a robust method to compensate for the effects of varying probe pressure.

LV volume quantification via spatiotemporal analysis of real-time 3-D echocardiography

This paper presents a method of four-dimensional (4-D) (3-D + Time) space-frequency analysis for directional denoising and enhancement of real-time three-dimensional (RT3D) ultrasound and quantitative measures in diagnostic cardiac ultrasound. Expansion of echocardiographic volumes is performed with complex exponential wavelet-like basis functions called brushlets. These functions offer good localization in time and frequency and decompose a signal into distinct patterns of oriented harmonics, which are invariant to intensity and contrast range. Deformable-model segmentation is carried out on denoised data after thresholding of transform coefficients. This process attenuates speckle noise while preserving cardiac structure location. The superiority of 4-D over 3-D analysis for decorrelating additive white noise and multiplicative speckle noise on a 4-D phantom volume expanding in time is demonstrated. Quantitative validation, computed for contours and volumes, is performed on in vitro balloon phantoms. Clinical applications of this spaciotemporal analysis tool are reported for six patient cases providing measures of left ventricular volumes and ejection fraction.

3D ultrasound measurement of large organ volume

Freehand 3D ultrasound is particularly appropriate for the measurement of organ volumes. For small organs, which can be fully examined with a single sweep of the ultrasound probe, the results are known to be much more accurate than those using conventional 2D ultrasound. However, large or complex shaped organs are difficult to quantify in this manner because multiple sweeps are required to cover the entire organ. Typically, there are significant registration errors between the various sweeps, which generate artifacts in an interpolated voxel array, making segmentation of the organ very difficult. This paper describes how sequential freehand 3D ultrasound, which does not employ an interpolated voxel array, can be used to measure the volume of large organs. Partial organ cross-sections can be segmented in the original B-scans, and then combined, without the need for image-based registration, to give the organ volume. The inherent accuracy (not including position sensor and segmentation errors) is demonstrated in simulation to be within +/- 2%. The in vivo precision of the complete system is demonstrated (by repeated observations of a human liver) to be +/- 5%.

Comparison of septal defects in 2D and 3D echocardiography using active contour models

Three-dimensional ultrasound is emerging as a viable resource for the imaging of internal organs. Quantitative studies correlating ultrasonic volume measurements with MRI data continue to validate this modality as a more efficient alternative for 3D imaging studies. However, the processing required to form 3D images from a set of 2D images may result in a loss of spatial resolution and may give rise to artifacts. This paper examines a method of automatic feature extraction and data quantification in 3D data sets as compared with original 2D data. This work will implement an active contour algorithm to automatically extract the endocardial borders of septal defects in echocardiographic images, and compare the size of the defects in the original 2D images and the 3D data sets.

Surface interpolation from sparse cross sections using region correspondence

The ability to estimate a surface from a set of cross sections allows calculation of the enclosed volume and the display of the surface in three-dimensions. This process has increasingly been used to derive useful information from medical data. However, extracting the cross sections (segmenting) can be very difficult, and automatic segmentation methods are not sufficiently robust to handle all situations. Hence, it is an advantage if the surface reconstruction algorithm can work effectively on a small number of cross sections. In addition, cross sections of medical data are often quite complex. Shape-based interpolation is a simple and elegant solution to this problem, although it has known limitations when handling complex shapes. In this paper, the shape-based interpolation paradigm is extended to interpolate a surface through sparse, complex cross sections, providing a significant improvement over our previously published maximal disc-guided interpolation. The performance of this algorithm is demonstrated on various types of medical data (X-ray computed tomography, magnetic resonance imaging and three-dimensional ultrasound). Although the correspondence problem in general remains unsolved, it is demonstrated that correct surfaces can be estimated from a limited amount of real data, through the use of region rather than object correspondence.

Body-centered visualisation for freehand 3-D ultrasound

Three-dimensional (3-D) ultrasound (US) data is typically visualised by any-plane slicing, volume rendering or surface rendering. Typical implementations of these techniques do not readily convey the spatial relationship between the visualised data and the patient's body, something that is particularly important when the data are reviewed after the scan has taken place, perhaps by a remote expert who did not even perform the scan. This paper describes a facility to register the 3-D US data to the patient's body and then display the data correctly superimposed on a rendered mannequin (rigid computer model). This way, the user can appreciate the position and orientation of any visualisation with respect to the patient's body. The facility relies on efficient implementation of progressive meshes to manage the level of detail of the mannequin model.

An interactive tool to visualize three-dimensional ultrasound data

Three-dimensional ultrasound can provide images that are easily understood by people who are not specialists in ultrasonography. However, current visualization methods do not perform very well on 3-D ultrasound data. Apart from some specific cases (obstetrics, cardiology), 3-D ultrasound images have not yet demonstrated major benefits from a clinical point of view. In this article, we introduce an interactive method that allows the user easily to produce 3-D images for each ultrasound examination. It is a two-step method. First, the user roughly segments the data by drawing three boundary curves in perpendicular planes. A ray-casting algorithm then automatically retrieves the details of the objects. Because it can be used routinely, this tool should help to evaluate the potential of 3-D ultrasonography.