Extended field of view sonography in musculoskeletal imaging

What is the place of ultrasound in MSK imaging?

During the past four decades, ultrasound has become popular as an imaging modality applied to the musculoskeletal (MSK) system, particularly outside the USA, due to its low cost, accessibility, and lack of ionizing radiation. A basic requirement in performing these examinations is to have a core group of radiologists and ultrasound technologists with expertise in MSK ultrasound. The extent to which ultrasound will be part of the imaging offered by a particular radiology practice or in an academic institution will vary according to expertise, availability, and reimbursements. A brief discussion of the technical capabilities of the current generation of ultrasound scanners will be followed by a description of some of the more prevalent MSK ultrasound imaging applications. The extent to which training to perform these exams within and outside of Radiology plays a role is discussed. Applications that are unique to ultrasound, such as dynamic evaluation of musculoskeletal anatomy and some, US-guided interventions are an important part of MSK imaging. Ultrasound is increasingly important in the assessment of superficial structures, such as tendons, small joints, and peripheral nerves. These applications help to establish the place of ultrasound as an important part of the Radiologists approach to MSK imaging. Outside of radiology, for a variety of clinical subspecialties, ultrasound already plays an integral role in MSK imaging.

Musculoskeletal ultrasound: a technical and historical perspective

During the past four decades, musculoskeletal ultrasound has become popular as an imaging modality due to its low cost, accessibility, and lack of ionizing radiation. The development of ultrasound technology was possible in large part due to concomitant advances in both solid-state electronics and signal processing. The invention of the transistor and digital computer in the late 1940s was integral in its development. Moore's prediction that the number of microprocessors on a chip would grow exponentially, resulting in progressive miniaturization in chip design and therefore increased computational power, added to these capabilities. The development of musculoskeletal ultrasound has paralleled technical advances in diagnostic ultrasound. The appearance of a large variety of transducer capabilities and rapid image processing along with the ability to assess vascularity and tissue properties has expanded and continues to expand the role of musculoskeletal ultrasound. It should also be noted that these developments have in large part been due to a number of individuals who had the insight to see the potential applications of this developing technology to a host of relevant clinical musculoskeletal problems. Exquisite high-resolution images of both deep and small superficial musculoskeletal anatomy, assessment of vascularity on a capillary level and tissue mechanical properties can be obtained. Ultrasound has also been recognized as the method of choice to perform a large variety of interventional procedures. A brief review of these technical developments, the timeline over which these improvements occurred, and the impact on musculoskeletal ultrasound is presented below.

Scoliotic Imaging With a Novel Double-Sweep 2.5-Dimensional Extended Field-of-View Ultrasound

Extended field-of-view ultrasound (US EFOV) imaging is a technique used extensively in the clinical field to attain interpretable panorama of anatomy; 2.5-D US EFOV has recently been proposed for spine imaging. In the original 2.5-D US EFOV, it makes use of a six degrees-of-freedom positional sensor attached to the US probe to record the corresponding position of each B-scan. By combining the positional information and the B-scan images, the 2.5-D EFOV can reconstruct a panorama on a curved image plane when the scanning trajectory of the US probe is curved. In this paper, an improved method based on the Bezier interpolation is proposed to better reconstruct 2.5-D US EFOV imaging, producing the panoramas with smoother texture and higher quality. To make it more applicable for scoliosis patients, we designed a novel method called double-sweep 2.5-D EFOV to better image the spinal tissues and easily compute the Cobb angle. In vitro and in vivo experiments demonstrated that the 2.5-D EFOV images obtained by the proposed method can present anatomical structures of the scanning region accurately.

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.

Ultrasonographic Imaging and Anti-inflammatory Therapy of Muscle and Tendon Injuries Using Polymer Nanoparticles

Ultrasonography is a reliable diagnostic modality for muscle and tendon injuries, but it has been challenging to find right diagnosis of minor musculoskeletal injuries by conventional ultrasonographic imaging. A large amount of hydrogen peroxide (H2O2) are known to be generated during tissue damages such as mechanical injury and therefore H2O2 holds great potential as a diagnostic and therapeutic marker for mechanical injuries in the musculoskeletal system. We previously developed poly(vanillyl alcohol-co-oxalate) (PVAX), which rapidly scavenges H2O2 and exerts antioxidant and anti-inflammatory activity in H2O2-associated diseases. Based on the notion that PVAX nanoparticles generate CO2 bubbles through H2O2-triggered hydrolysis, we postulated that PVAX nanoparticles could serve as ultrasonographic contrast agents and therapeutic agents for musculoskeletal injuries associated with overproduction of H2O2. In the agarose gel phantom study, PVAX nanoparticles continuously generated CO2 bubbles to enhance ultrasonographic echogenicity significantly. Contusion injury significantly elevated the level of H2O2 in skeletal muscles and Achilles tendons. Upon intramuscular injection, PVAX nanoparticles significantly elevated the ultrasound contrast and suppressed inflammation and apoptosis in the contusion injury of musculoskeletal systems. We anticipate that PVAX nanoparticles hold great translational potential as theranostic agents for musculoskeletal injuries.

Imaging of muscle injury in the elite athlete

Injuries to muscle in the elite athlete are common and may be responsible for prolonged periods of loss of competitive activity. The implications for the athlete and his/her coach and team may be catastrophic if the injury occurs at a critical time in the athlete's diary. Imaging now plays a crucial role in diagnosis, prognostication and management of athletes with muscle injuries. This article discusses the methods available to clinicians and radiologists that are used to assess skeletal muscle injury. The spectrum of muscle injuries sustained in the elite athlete population is both discussed and illustrated.

A novel sonographic method of measuring patellar tendon length

Obtaining accurate and readily repeatable measurements is a prerequisite for using measures of soft tissue structures both clinically and in the research setting. Few studies have evaluated the interrater reliability of ultrasound measurements of tendons. The objective of this study was to determine the accuracy and reliability of a new method of sonographic measurement of patellar tendon length using direct dissection as the gold standard. Four cadaveric knees were sonographically evaluated by two independent investigators. Two custom designed straps with nylon strapping and stainless steel wire were used to firmly mark position on the leg and create an acoustic shadow on the ultrasound image. Anatomic landmarks were the distal patellar pole and the bony ridge on the anterior proximal tibia. After sonographic evaluation, the knee was dissected to expose the patellar tendon, which was measured using digital calipers. Intraclass correlation coefficients (ICC) were used to determine reliability of measurements between observers, where ICC >0.75 was considered good and >0.9 was considered excellent. Validity was measured using a Bland-Altman plot, which measures bias between measurement methods as well as variability of scatter. Three sonographic measurements were made by each investigator on each tendon. The length of each of the four tendons based on the mean values of sonographic measurements was 53.8 mm, 53.4 mm, 49.4 mm and 46.8 mm. The length based on visual inspection of the dissected tissue was 54.6 mm, 52.8 mm, 49.8 mm and 46.9 mm. The calculated ICC between raters was 0.96. On the Bland-Altman plot, the bias, or mean difference between sonographic and visual measures, was 0.17 mm, with a standard deviation of 0.71. The 95% limit of agreement was -1.55 to 1.22 mm. Measurement of patellar tendon length with ultrasound using adjustable surface markers and calipers is highly accurate and has good interrater reliability.

Extended Field-of-View Sonography: Evaluation of the Superficial Lesions

Objective

To evaluate the usefulness of extended-field-of-view 2-dimensional ultrasonography technique in superficial lesions.

Methods

During a 6-month period, 44 patients with superficial lesions on various parts of their bodies were evaluated with extended-field-of-view ultrasonography in addition to routine traditional 2-dimensional ultrasonography. If the diagnosis could not be made without the extended-field-of-view images, it was considered diagnostic. The radiologist decided if the extended-field-of-view ultrasonography helped spatial orientation, communicate findings, or compare the contralateral side in a single image, or if it was useful for follow-up evaluation.

Results

By using extended-field-of-view imaging including the surrounding anatomy, 22 musculoskeletal, 8 scrotal, 8 thyroid, 2 breast, and 4 abdominal wall lesions were documented successfully as a single image. Nevertheless, no new cases were diagnosed solely based on the extended-field-of-view images. Extended-field-of-view ultrasonography was considered helpful for spatial orientation in 25 cases (56.8%), for comparing the contralateral side in 16 cases (36.3%), and for communicating findings in 20 cases (45.4%). It was useful for follow-up evaluation in 13 cases (29.5%).

Conclusions

None of the extended-field-of-view images was diagnostic. However, they did provide valuable additional information and better documentation of the lesions.

Interobserver and Intraobserver Variability in the Sonographic Measurement of the Size of the Thyroid Gland by Extended Field-of-View Sonography

Significant intra- and interobserver variation has been reported for estimating the dimensions and the volume of the thyroid gland by conventional sonography in adults. This study aimed to assess the role of extended field-of-view (EFOV) sonography for evaluating the size of the thyroid gland. The mediolateral, anteroposterior, and craniocaudal diameters of both thyroid lobes as well as total thyroid volumes of 30 female patients with the clinical diagnosis of goiter were measured three times by three radiologists with the EFOV sonography technique. Based on these findings, the correlation between the measurements of different operators and different measurements of the same operator was investigated. The interobserver variations for craniocaudal diameters of the right and left thyroid lobes were 3.3% ± 1.9% (mean ± SD) and 2.8% ± 1.3% (mean ± SD), respectively ( P = .012), which were lower than the variations calculated for transverse and mediolateral diameters. The interobserver variation for the calculation of the total glandular volume was 6.3% ± 3.8% (mean ± SD). The intraobserver variations for the three radiologists assessing the total thyroid volume were 4.9% ± 3.0%, 4.2% ± 2.4%, and 4.5% ± 1.7% (all mean ± SD), respectively ( P = .521). EFOV sonography should be considered as an alternative technique for the dimension measurements of the thyroid gland, particularly in cases with goiter.

Fetal thermal effects of diagnostic ultrasound

Processes that can produce a biological effect with some degree of heating (ie, about 1 degrees C above the physiologic temperature) act via a thermal mechanism. Investigations with laboratory animals have documented that pulsed ultrasound can produce elevations of temperature and damage in biological tissues in vivo, particularly in the presence of bone (intracranial temperature elevation). Acoustic outputs used to induce these adverse bioeffects are within the diagnostic range, although exposure times are usually considerably longer than in clinical practice. Conditions present in early pregnancy, such as lack of perfusion, may favor bioeffects. Thermally induced teratogenesis has been shown in many animal studies, as well as several controlled human studies; however, human studies have not shown a causal relationship between diagnostic ultrasound exposure during pregnancy and adverse biological effects to the fetus. All human epidemiologic studies, however, were conducted with commercially available devices predating 1992, that is, with acoustic outputs not exceeding a spatial-peak temporal-average intensity of 94 mW/cm2. Current limits in the United States allow a spatial-peak temporal-average intensity of 720 mW/cm2 for fetal applications. The synergistic effect of a raised body temperature (febrile status) and ultrasound insonation has not been examined in depth. Available evidence, experimental or epidemiologic, is insufficient to conclude that there is a causal relationship between obstetric diagnostic ultrasound exposure and obvious adverse thermal effects to the fetus. However, very subtle effects cannot be ruled out and indicate a need for further research, although research in humans may be extremely difficult to realize.

Does extended-field-of-view sonography improve interrater reliability for the detection of rotator cuff muscle atrophy?

OBJECTIVE

Assessment of rotator cuff muscle atrophy is an important component of the shoulder sonogram. We hypothesized that extended-field-of-view (EFOV) sonography would allow greater interrater reliability than conventional sonography for the evaluation of rotator cuff muscle atrophy.

MATERIALS AND METHODS

This retrospective study involved 50 consecutive patients who presented for shoulder sonography. All patients underwent EFOV imaging of the supraspinatus and infraspinatus muscles in addition to conventional imaging of each muscle. Five musculoskeletal radiologists first assessed 50 EFOV images of the supraspinatus and infraspinatus muscles and scored both muscles using a scale of 1-5. The reliability of each method was determined by calculating intraclass correlation coefficients (ICCs) according to a method developed by Shrout and Fleiss. The significance of the difference between reliabilities for conventional images and EFOV images was tested with a z-test.

RESULTS

For the EFOV images, the ICC for the supraspinatus muscle was 0.77 and for the infraspinatus, 0.75. For the conventional images, the ICC for the supraspinatus muscle was 0.52 and for the infraspinatus, 0.57. The degree of interrater reliability for the five readers in our study was significantly higher for the EFOV images than for the conventional images (p < 0.0001).

CONCLUSION

EFOV sonography results in greater interrater reliability than conventional sonography for the detection of rotator cuff muscle atrophy. EFOV images of the rotator cuff muscles should be obtained as part of routine shoulder sonography.

Three-dimensional extended field-of-view ultrasound

Three-dimensional (3-D) extended field-of-view ultrasound creates a mosaic view from a set of volumes acquired from a dedicated 3-D ultrasound machine combined with a position tracker. A simple compounding technique can be used to combine the volumes together using only the position measurements, but some misalignment remains. Two different registration methods were developed to correct these errors in the overlapping regions. The first method divides the overlap into smaller blocks and warps the blocks to best align the features. The second method is similar, but uses rigid body registration of the blocks. Experiments in vitro and in vivo showed that block-based registration with warping produced the most reproducible results and the greatest increase in similarity among the overlapping regions. It also produced the best reconstruction accuracy, with a mean distance error of 0.4 mm measured across 101.78 mm in a phantom, representing 0.4% error.

The use of ultrasound in evaluating orthopaedic trauma patients

Musculoskeletal ultrasound is a low-cost, noninvasive method of evaluating orthopaedic trauma patients. It is particularly useful for patients with metallic hardware, which may degrade computed tomography or magnetic resonance images. Ultrasound has been used to evaluate fracture union and nonunion, infection, ligamentous injury, nerve compression, and mechanical impingement caused by hardware. Real-time dynamic examination allows identification of pathology and provides direct correlation between symptoms and the observed pathology.

3-D measurement of body tissues based on ultrasound images with 3-D spatial information

In this study, we developed a new method to perform 3-D measurements between the recorded B-scans using the corresponding spatial location and orientation of each B-scan, without the need to create a 3-D volume. A portable ultrasound (US) scanner and an electromagnetic spatial locator attached to the US probe were used. During data collection, the US probe was moved over the region-of-interest. A small number of B-scans containing interesting anatomical information were captured from different body parts and displayed in a 3-D space with their corresponding locations recorded by the spatial locator. In the B-scan planes, the distance between any two points, as well as the angle between any two lines, could be calculated. In validation experiments, three distances and three angles of a custom-designed phantom were measured using this method. In comparison with the results measured by a micrometer, the mean error of distance measurement was -0.8 +/- 1.7 mm (-2.3 +/- 3.6%) and that of angle measurement was -0.3 +/- 2.9 degrees (-0.1 +/- 4.1%). The lengths of the first metatarsals and the angles between the first metatarsals and the middle part of the tibias of three subjects were measured in vivo using magnetic resonance imaging (MRI) and the US method by two operators before and after MRI scanning. The overall percentage differences of the length and angle measurements were 0.8 +/- 2.2% and 2.5 +/- 3.6%, respectively. The results showed that this US method had good repeatability and reproducibility (interclass correlation coefficient values > 0.75). We expect that this new method could potentially provide a quick and effective approach for the 3-D measurement of soft tissues and bones in the musculoskeletal system.

Comparison of extended field of view and dual image ultrasound techniques: accuracy and reliability of distance measurements in phantom study

This study was undertaken to investigate and compare the accuracy and reliability of dual image and extended field-of-view (EFOV) ultrasound (US) techniques in distance measurements using acoustic phantoms. Ten tissue phantoms were constructed and were scanned twice with an interval of 3 days by two operators. Measurements of various known distance (ranging from 4.6 to 7.2 cm) in the phantoms were made with dual image and EFOV US. Results showed that both dual image and EFOV US have a high accuracy and reliability in distance measurements, with the EFOV US (r = 0.997 to 0.998, reproducibility = 99.8%, repeatability = 98.2 to 99.8%) being slightly more accurate and reliable than dual image US (r = 0.948 to 0.981, reproducibility = 94.6%, repeatability = 89.6 to 97.9%). EFOV US has a higher accuracy and reliability than dual image US in distance measurements. However, the dual image US is a useful alternative with a high accuracy and reliability when EFOV US is not available.

Extended field-of-view sonography: advantages in abdominal applications

OBJECTIVE

To show the advantages of extended field-of-view sonography in abdominal applications.

METHODS

Thirty-one cases were prospectively analyzed in our study. Extended field-of-view images were obtained when the radiologist decided that they would offer potential advantages for the examination. When extended field-of-view scanning was used, the radiologist determined prospectively whether it was useful according to several categories. Images were obtained with a 2- to 5-MHz curved array transducer or 4- to 9- and 5- to 12-MHz linear array transducers.

RESULTS

Extended field-of-view sonography provided several potential benefits over conventional sonography in the abdominal area. The advantages of extended field-of-view sonography were better demonstration of the spatial relationship between lesions and adjacent normal structures in 18 cases (58%), accurate quantification of sizes or volumes of large organs or lesions in 16 (52%), better display of the extended and tubular structures in 6 (19%), usefulness for clinical consultations in 7 (23%), and documentation comparable with that of computed tomography or magnetic resonance imaging in 10 (32%).

CONCLUSIONS

Extended field-of-view sonography provided the anatomic context of the lesion in its surroundings and allowed precise measurement and tracing of the extended and tubular structures. The method has notable advantages and clinical applications.

The value of ultrasound in sports medicine

Musculoskeletal ultrasound is increasingly being used in the evaluation and treatment of sports-related injuries. This technique is widely available, rapid, and has a high patient acceptance. Its multiplanar capability and dynamic real-time imaging can be correlated with clinical symptoms and compared to contralateral asymptomatic structures.

Three-dimensional ultrasonography of bone and soft tissue lesions

BACKGROUND

The aim of this study was to investigate feasibility and potential applications of three-dimensional (3D) ultrasonography in the evaluation of musculoskeletal disorders.

METHODS

3D ultrasonography was performed in 83 patients with bone (n = 50) or soft tissue lesions (n = 33). Volume data were obtained using two volume probes (1-8.5 and 8.5-12 MHz) and a 3D ultrasound unit. The results of 3D ultrasonography were compared to two-dimensional ultrasound and radiological imaging.

RESULTS

The system enabled acquisition of 3D ultrasound data in diagnostic quality. 3D image-processing permits to analyse ultrasound data interactively in three orthogonal planes (section mode) or in realistic 3D views (rendering mode). Compared to conventional ultrasonography 3D image analysis improved assessment of details, provided better spatial orientation and facilitated image interpretation in 23, 44 and 49 cases, respectively. Additional findings that had significant influence on patient management were obtained in 16 of 83 patients (19%). Multiplanar reformating provided additional scan planes and increased the comparability of follow up examinations by standardized display and measurement. 3D surface reconstructions were very helpful to understand the morphology of bone lesions e.g. tortuous fracture lines.

CONCLUSION

Our preliminary experience shows that 3D ultrasonography of musculoskeletal disorders is feasible. The ability to assess previously unattainable scan planes and lifelike surface projections may be particularly valuable for imaging of bone lesions. Further studies will be required to assess the exact role of this new technique for the evaluation of musculoskeletal disorders.

Hand and wrist sonography

Although the anatomy of the hand and wrist is complex and the pathologic conditions encountered are diverse, many of the disease processes are localized, and in many situations, the clinical question is specific and limited. Because of this, ultrasound has always been an attractive imaging modality for evaluation of hand and wrist problems. Unfortunately, intrinsic difficulties in ultrasound image acquisition and interpretation have slowed the acceptance of hand and wrist sonography. Recently, however, new developments in high-resolution transducers and signal processing have dramatically improved image quality and scanning flexibility. For this reason, hand and wrist sonography is now more widely accepted and is taking its place along side other traditional modalities such as radiography, computed tomography, magnetic resonance imaging, and arthrography. Specific situations in which ultrasound offers definite benefits include evaluation of tendon inflammation and rupture, evaluation of palpable masses or suspected occult masses, and evaluation of suspected foreign bodies. Analysis of the median nerve is also possible and in the future, may have a role in patients with carpal tunnel syndrome.

Extended field-of-view ultrasound

When ultrasound became a clinical reality in the 1970s, extended field of view was the only form of imaging available because all ultrasound images were created with articulated arm scanners that encompassed the area of interest in its entirety. With the advent of high-quality real-time imaging in the 1980s, the extended field of view was lost, and with it went an important diagnostic component as well as an important means of communicating diagnostic findings to referring clinicians. Through the magic of computer technology, extended field of view imaging is back! Extended field of view images can now be created very easily and conveniently, in real time. The convenience and accuracy of real-time imaging is maintained while important anatomical perspectives are added. This article reviews the status of real-time extended field of view sonography. The technical details as well as the clinical relevance of this method are summarized. The day-to-day clinical utility of extended field of view imaging is liberally illustrated.

Color-SieScape imaging of carotid and vertebral arteries

OBJECTIVE

The aim of this study was to estimate the feasibility and limitations of Color-SieScape imaging of carotid and vertebral arteries in healthy subjects.

METHODS

extended field of view procedure was applied during the examination of 80 carotid and 80 vertebral arteries in 40 healthy volunteers.

RESULTS

visualisation of a common carotid artery together with a proximal segment of both an internal (ICA) and external carotid artery (ECA) in one Color-SieScape image was possible in nine cases. Clear presentation of a common carotid artery in one Color-SieScape image with a segment of an ICA or ECA of varying length was possible in 49 cases. In 22 cases, visualisation of an ICA was possible only on a minimal length, with major artefacts or completely impossible. Color-SieScape images of vertebral arteries were good or very good in 34 cases and poor or very poor in 46 cases. Artefacts arose due to the pulsatile movements of the arterial wall, especially in vessels lying close to the skin and in the proximal part of a common carotid artery. Tracing a tortuous vessel and ICA coming from common carotid artery at an angle close to 90 degrees produced significant artefacts.

CONCLUSIONS

Color-SieScape images of carotid and vertebral arteries of good quality are usually possible to obtain.