Real-time three-dimensional ultrasound methods for shape analysis and visualization

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.

Ultrasound Imaging in Radiation Therapy: From Interfractional to Intrafractional Guidance

External beam radiation therapy (EBRT) is included in the treatment regimen of the majority of cancer patients. With the proliferation of hypofractionated radiotherapy treatment regimens, such as stereotactic body radiation therapy (SBRT), interfractional and intrafractional imaging technologies are becoming increasingly critical to ensure safe and effective treatment delivery. Ultrasound (US)-based image guidance systems offer real-time, markerless, volumetric imaging with excellent soft tissue contrast, overcoming the limitations of traditional X-ray or computed tomography (CT)-based guidance for abdominal and pelvic cancer sites, such as the liver and prostate. Interfractional US guidance systems have been commercially adopted for patient positioning but suffer from systematic positioning errors induced by probe pressure. More recently, several research groups have introduced concepts for intrafractional US guidance systems leveraging robotic probe placement technology and real-time soft tissue tracking software. This paper reviews various commercial and research-level US guidance systems used in radiation therapy, with an emphasis on hardware and software technologies that enable the deployment of US imaging within the radiotherapy environment and workflow. Previously unpublished material on tissue tracking systems and robotic probe manipulators under development by our group is also included.

Review of ultrasound image guidance in external beam radiotherapy: I. Treatment planning and inter-fraction motion management

In modern radiotherapy, verification of the treatment to ensure the target receives the prescribed dose and normal tissues are optimally spared has become essential. Several forms of image guidance are available for this purpose. The most commonly used forms of image guidance are based on kilovolt or megavolt x-ray imaging. Image guidance can also be performed with non-harmful ultrasound (US) waves. This increasingly used technique has the potential to offer both anatomical and functional information.This review presents an overview of the historical and current use of two-dimensional and three-dimensional US imaging for treatment verification in radiotherapy. The US technology and the implementation in the radiotherapy workflow are described. The use of US guidance in the treatment planning process is discussed. The role of US technology in inter-fraction motion monitoring and management is explained, and clinical studies of applications in areas such as the pelvis, abdomen and breast are reviewed. A companion review paper (O'Shea et al 2015 Phys. Med. Biol. submitted) will extensively discuss the use of US imaging for intra-fraction motion quantification and novel applications of US technology to RT.

Applications of 2-dimensional matrix array for 3- and 4-dimensional examination of the fetus: a pictorial essay

OBJECTIVES

Two-dimensional (2D) matrix array is a new technology for the performance of 3-dimensional and 4-dimensional (4D) ultrasonography. In this study, we report the use of a 2D matrix array transducer for examination of fetal structures including the fetal heart.

METHODS

Thirty-four fetuses without abnormalities and 19 fetuses with congenital anomalies were examined with a 2D matrix array transducer (x3-1, IE-33; Philips Medical Systems, Bothell, WA). Median gestational age was 25 6/7 weeks (range, 13 0/7-40 1/7 weeks).

RESULTS

(1) A 360 degrees rotation and examination of selected structures was possible in the second trimester. (2) Structures were examined by maintaining the transducer in a fixed position and rotating the volume using the system trackball. (3) Dorsal and ventral parts of the hands and feet were visualized in a single volume data set, in real time, without moving the transducer. (4) Real-time en face visualization of atrioventricular valves was possible from the ventricular or atrial chambers. (5) Four-dimensional images of bones were obtained by decreasing gain settings only, with no need for cropping. (6) Four-dimensional reconstruction of vascular structures was possible with color Doppler imaging. Two limitations were identified: (1) lower resolution than mechanical volumetric transducers, and (2) narrow volume display.

CONCLUSIONS

Real-time direct 4D imaging with 360 degrees rotation for examination of fetal anatomic structures is feasible. This technology allows examination of fetal structures from multiple perspectives, in real time, without the need to move the transducer in the maternal abdomen. Further technological developments may overcome the limitations identified in this study.

Four-dimensional ultrasonography for dynamic bladder shape visualization and analysis during voiding

OBJECTIVE

The purpose of this study was to describe initial applications of 4-dimensional ultrasonography (4DUS) for visualizing dynamic change in 3-dimensional (3D) bladder shape as well as for analyzing intravesical volume and diameters during voiding.

METHODS

In 15 healthy volunteers and 5 patients with lower urinary tract symptoms, 4DUS images of the bladder during voiding were obtained by transabdominal 4DUS and compared with the outcome of uroflowmetry. Changes of intravesical volume as well as diameters in axial, coronal, and sagittal planes were measured and analyzed in comparison with uroflow data.

RESULTS

Dynamic 3D visualization of the bladder shape was feasible in all 20 men. Multiplanar display of 4DUS showed dynamic 3D images of the bladder during voiding to be simultaneously visualized in the axial, coronal, and sagittal planes. The change and decrease rate in intravesical volume calculated by 4DUS data had significant correlation with the average flow rate (P = .02) and the maximum flow rate (P = .04), respectively. Among the 3 diameters, the change of coronal diameter was significantly most correlated with change of the intravesical volume (P < .0001). The change in coronal diameter, which was observed in patients with urinary disturbance, had a significant difference compared with those observed in control subjects (P = .01).

CONCLUSIONS

Monitoring of voiding with 4DUS was feasible in healthy men and patients with lower urinary tract symptoms. Four-dimensional ultrasonography has the potential to be a novel noninvasive urodynamic modality to visualize dynamically the lower urinary tract during voiding and to improve pathophysiologic understanding of voiding.

Outer shape changes of human masseter with contraction by ultrasound morphometry

OBJECTIVE

The multipennate masseter has a complex internal architecture, which suggests the contraction is not uniform within the muscle. The heterogeneous contraction may cause inequable changes of the muscle's outer shape. This study aimed to elucidate the outer shape changes of the whole masseter with clenching by multipoint measurement of serial ultrasound images.

DESIGN

Serial coronal images (perpendicular to the FH plane, 3 mm interval) of the right masseter of five healthy men were obtained with a real-time ultrasonograph equipped with a 13 MHz linear-array transducer. To define the relationship between the transducer and cranium, we used a 3D mechanical stage with a face-bow. Registrations were made during muscle relaxation and maximal clenching. The distance between the lateral and medial outlines of the muscle was measured at intervals of 1mm from the origin to insertion in each image as the thickness at the corresponding measured point.

RESULTS

The thickness of the relaxed and contracted muscle (R and C) and its difference (Delta) varied among the measured points. Muscle thickness at most measured sites increased with clenching, whereas it decreased at several sites, mainly near the origin and insertion. There were positive correlations in every subject both between R and C, and between C and Delta. On the other hand, the correlation between R and Delta were negative or weak.

CONCLUSION

Changes of thickness with clenching showed great disparity within the masseter, which may result from the complexity of the contraction properties due to the multipennate structure and functional heterogeneity.

Ultrasound imaging of the pelvic floor. Part II: three-dimensional or volume imaging

In this second part of a review of pelvic floor ultrasound imaging, current three-dimensional (3D) ultrasound technology and its use for imaging pelvic floor structure and function is described. Recent technical developments enable rapid automated volume acquisition in real time, and currently available transducers designed for abdominal use are well suited for translabial/transperineal imaging. To date, such systems have been used to image the urethra, the levator ani and paravaginal supports, prolapse and implants used in pelvic floor reconstruction and anti-incontinence surgery. While 3D pelvic floor imaging is a field that is still in its infancy, it is already clear that the method has opened up entirely new opportunities for the observation of functional anatomy.

Determination of Asymmetric Cavity Volumes Using Real-Time Three-Dimensional Echocardiography: An In Vitro Balloon Model Study

OBJECTIVES

We designed a new in vitro model to test the accuracy and reproducibility of real-time three-dimensional (RT3D) ultrasound imaging for determining a variety of asymmetric cavity volumes with aneurysm.

METHODS

Fifteen individual balloon models mimicking ventricular aneurysm were filled with water (170-322.5 ml) without air bubbles and kept in a compressor pump. Compression of the models produced only a change in shape of the balloon and no change in volume. The models were scanned with RT3D echocardiography (RT3DE) and the images recorded on an optical disk. Volumes were measured off line in two phases; maximal compression, where there was maximal change in shape and nil compression, where there was minimal or no change in shape. Volumes were measured by manual tracing technique of the inner border of B-scan images and compared with the drained volume of water from the balloon.

RESULTS

There was a high correlation between the drained volume and measured volume at maximal compression (equivalent to end-systole, r = 0.99, y = 0.99x + 3.69, SEE = 6.5 ml), between the drained volume and measured volume at nil compression (equivalent to end-diastole, r = 0.99, y = 0.94x + 12.07, SEE = 5.9 ml), and between volumes measured at maximal and nil compressions (r = 0.99, y = 0.94x + 10.55, SEE = 4.6 ml).

CONCLUSION

The results of this experiment show that RT3DE can accurately measure the volumes of a variety of asymmetric ventricular cavities.

Four-dimensional ultrasonography of the fetal heart with spatiotemporal image correlation

OBJECTIVE

This study was undertaken to describe a new technique for the examination of the fetal heart using four-dimensional ultrasonography with spatiotemporal image correlation (STIC).

STUDY DESIGN

Volume data sets of the fetal heart were acquired with a new cardiac gating technique (STIC), which uses automated transverse and longitudinal sweeps of the anterior chest wall. These volumes were obtained from 69 fetuses: 35 normal, 16 with congenital anomalies not affecting the cardiovascular system, and 18 with cardiac abnormalities. Dynamic multiplanar slicing and surface rendering of cardiac structures were performed. To illustrate the STIC technique, two representative volumes from a normal fetus were compared with volumes obtained from fetuses with the following congenital heart anomalies: atrioventricular septal defect, tricuspid stenosis, tricuspid atresia, and interrupted inferior vena cava with abnormal venous drainage.

RESULTS

Volume datasets obtained with a transverse sweep were utilized to demonstrate the cardiac chambers, moderator band, interatrial and interventricular septae, atrioventricular valves, pulmonary veins, and outflow tracts. With the use of a reference dot to navigate the four-chamber view, intracardiac structures could be simultaneously studied in three orthogonal planes. The same volume dataset was used for surface rendering of the atrioventricular valves. The aortic and ductal arches were best visualized when the original plane of acquisition was sagittal. Volumes could be interactively manipulated to simultaneously visualize both outflow tracts, in addition to the aortic and ductal arches. Novel views of specific structures were generated. For example, the location and extent of a ventricular septal defect was imaged in a sagittal view of the interventricular septum. Furthermore, surface-rendered images of the atrioventricular valves were employed to distinguish between normal and pathologic conditions. Representative video clips were posted on the Journal's Web site to demonstrate the diagnostic capabilities of this new technique.

CONCLUSION

Dynamic multiplanar slicing and surface rendering of the fetal heart are feasible with STIC technology. One good quality volume dataset, obtained from a transverse sweep, can be used to examine the four-chamber view and the outflow tracts. This novel method may assist in the evaluation of fetal cardiac anatomy.