3DUS System Research Articles

Intraoperative visualization of cerebral aneurysms using navigated 3D-ultrasound power-Doppler angiography.

The questions of whether the spatial resolution of navigated 3D-ultrasound (3D-US) power-Doppler angiography imaging rendered by existing 3D-US systems is sufficient for the intraoperative visualization of cerebral aneurysms, and in what percentage of cases, are largely unanswered. A study on this topic is lacking in the literature. From 2015 to 2022, we performed 86 surgeries on 83 aneurysm patients. Navigated 3D-US was used at the discretion of the operating neurosurgeons when available (i.e., not being used during parallel tumor surgeries). Twenty-five aneurysms (15 ruptured) were operated on using 3D-US; 22 aneurysms were located at the middle cerebral artery (MCA). Patient 3D-US power-Doppler angiography images and surgical reports were retrospectively reviewed to assess the intraoperative ultrasound visibility of aneurysms. In 20 patients (80%) the aneurysms were successfully visualized. In five patients (20%), the aneurysms visualization was insufficient or absent. Nineteen of 22 aneurysms (86.4%) were visualized in the MCA aneurysm subgroup. We observed no association between aneurysm visibility and aneurysm size or the presence of subarachnoid hemorrhage. In the subgroup of MCA aneurysms, no association between aneurysm visibility and the presence of subarachnoid hemorrhage was found; a trend toward poor sonographic visibility of smaller aneurysms was observed (p = 0.09). Our initial data show that intraoperative 3D-US power-Doppler angiography, rendered by current navigated 3D-US systems, clearly depicts the majority of aneurysms in the MCA aneurysm subgroup. However, future prospective studies performed on a higher number of aneurysms localized at various anatomic sites are needed to confirm our initial findings and determine their potential clinical relevance.

Validity of Freehand 3-D Ultrasound System in Measurement of the 3-D Surface Shape of Shoulder Muscles.

Freehand 3-D ultrasound (3DUS) system is a promising technique for accurately assessing muscle morphology. However, its accuracy has been validated mainly in terms of volume by examining lower limb muscles. This study was aimed at validating 3DUS in the measurements of 3-D surface shape and volume by comparing them with magnetic resonance imaging (MRI) measurements while ensuring the reproducibility of participant posture by focusing on the shoulder muscles. The supraspinatus, infraspinatus and posterior deltoid muscles of 10 healthy men were scanned using 3DUS and MRI while secured by an immobilization support customized for each participant. A 3-D surface model of each muscle was created from the 3DUS and MRI methods, and the agreement between them was assessed. For the muscle volume, the mean difference between the two models was within -0.51 cm3. For the 3-D surface shape, the distances between the closest points of the two models and the Dice similarity coefficient were calculated. The results indicated that the median surface distance was less than 1.12 mm and the Dice similarity coefficient was larger than 0.85. These results suggest that, given the aforementioned error is permitted, 3DUS can be used as an alternative to MRI in measuring volume and surface shape, even for the shoulder muscles.

Spatially tracked whole-breast three-dimensional ultrasound system toward point-of-care breast cancer screening in high-risk women with dense breasts.

Mammographic screening has reduced mortality in women through the early detection of breast cancer. However, the sensitivity for breast cancer detection is significantly reduced in women with dense breasts, in addition to being an independent risk factor. Ultrasound (US) has been proven effective in detecting small, early-stage, and invasive cancers in women with dense breasts. To develop an alternative, versatile, and cost-effective spatially tracked three-dimensional (3D) US system for whole-breast imaging. This paper describes the design, development, and validation of the spatially tracked 3DUS system, including its components for spatial tracking, multi-image registration and fusion, feasibility for whole-breast 3DUS imaging and multi-planar visualization in tissue-mimicking phantoms, and a proof-of-concept healthy volunteer study. The spatially tracked 3DUS system contains (a) a six-axis manipulator and counterbalanced stabilizer, (b) an in-house quick-release 3DUS scanner, adaptable to any commercially available US system, and removable, allowing for handheld 3DUS acquisition and two-dimensional US imaging, and (c) custom software for 3D tracking, 3DUS reconstruction, visualization, and spatial-based multi-image registration and fusion of 3DUS images for whole-breast imaging. Spatial tracking of the 3D position and orientation of the system and its joints (J1-6 ) were evaluated in a clinically accessible workspace for bedside point-of-care (POC) imaging. Multi-image registration and fusion of acquired 3DUS images were assessed with a quadrants-based protocol in tissue-mimicking phantoms and the target registration error (TRE) was quantified. Whole-breast 3DUS imaging and multi-planar visualization were evaluated with a tissue-mimicking breast phantom. Feasibility for spatially tracked whole-breast 3DUS imaging was assessed in a proof-of-concept healthy male and female volunteer study. Mean tracking errors were 0.87 ± 0.52, 0.70 ± 0.46, 0.53 ± 0.48, 0.34 ± 0.32, 0.43 ± 0.28, and 0.78 ± 0.54mm for joints J1-6 , respectively. Lookup table (LUT) corrections minimized the error in joints J1 , J2 , and J5 . Compound motions exercising all joints simultaneously resulted in a mean tracking error of 1.08 ± 0.88mm (N=20) within the overall workspace for bedside 3DUS imaging. Multi-image registration and fusion of two acquired 3DUS images resulted in a mean TRE of 1.28 ± 0.10mm. Whole-breast 3DUS imaging and multi-planar visualization in axial, sagittal, and coronal views were demonstrated with the tissue-mimicking breast phantom. The feasibility of the whole-breast 3DUS approach was demonstrated in healthy male and female volunteers. In the male volunteer, the high-resolution whole-breast 3DUS acquisition protocol was optimized without the added complexities of curvature and tissue deformations. With small post-acquisition corrections for motion, whole-breast 3DUS imaging was performed on the healthy female volunteer showing relevant anatomical structures and details. Our spatially tracked 3DUS system shows potential utility as an alternative, accurate, and feasible whole-breast approach with the capability for bedside POC imaging. Future work is focused on reducing misregistration errors due to motion and tissue deformations, to develop a robust spatially tracked whole-breast 3DUS acquisition protocol, then exploring its clinical utility for screening high-risk women with dense breasts.

Validation of a three dimensional musculoskeletal ultrasound system for use in hands and wrists

Purpose: The effect of chronic synovitis on the progression of osteoarthritis pathology is a relatively new but supported concept in the fields of rheumatology and hand surgery that has been linked to pain and disability in patients. Currently, the gold standard for diagnosing synovitis in the wrists and hands is a clinical examination and the use of 2 dimensional (2D) musculoskeletal ultrasound imaging (US). Major limitations associated with this method are the lack of quantitative measurement tools available and the fact that physicians have to be able to mentally reconstruct the patient’s 3-dimensional anatomy from the 2-dimensional images provided. These limitations can be overcome by using a 3-dimensional ultrasound (3DUS) system to quantitatively measure the size of synovial hypertrophy, effusions, ganglions and osteophytes as well as having a 3D reconstruction of the patient’s hand. The aim of this work is to develop a 3D ultrasound system for imaging the hand and wrist. This paper reports on the development, geometric, and volumetric validation for wrist/hand 3D ultrasound imaging. Methods: A mechatronic wrist/hand imaging system was designed and created to operate with a conventional 2D US imaging system. The scanning system features a motor which contains a single integrated electromagnetic encoder that records the rotational position of the motor. This motor drives a lead screw which in turn moves the transducer, which is submerged in a water bath, along the linear axis to acquire a series of 2D images. The encoder information provides the software with the position of each 2D ultrasound frame. These conventional diagnostic 2D US images are then reconstructed into a 3D US images from a licensed ultrasound machine. The geometric validation of the system was done using a multi-layered monofilament grid phantom with spacings of 10 mm and the Euclidean distances between the wires were measured. The volumetric validation was conducted using a simulated synovial tissue phantom and the images were analyzed using 3D-Slicer to manually segment individual slices in the 3D image. These slices were then interpolated to construct a 3D segmentation of the phantom. This process was repeated over four days to test the intra-rater reliability of the system. The 3D volumes were compared to those found using magnetic resonance imaging (MRI) and the known volume of the agar phantom. Results: The largest error and variance recorded from the geometric validation measurements was 0.0856± 0.0087mm and was acquired from the reconstruction plane. The remaining linear measurement errors were all < 1%. The error between the mean phantom volume measurements and the known synovium phantom volume was 5.99% and 2.43% for the 3D US device and MRI respectively. Linear regression for volumetric measures revealed an R2 value of 0.4736 with a p-value of 0.20, revealing no significant correlation between the measurements made over the course of 4 days for the 3D US device. The percent difference in the volume measurements from the 3D US device and MRI was 0.814%. Conclusions: A mechatronic 3D ultrasound imaging system was developed for the wrist and hand. Successful geometric and volumetric validation demonstrates feasibility for implementation in a clinical setting. Current work evaluates system ability to accurately and quantitatively classify synovitis in first carpometacarpal joint and distal radial injury patients to investigate the relationship between chronic inflammation and the progression of osteoarthritis in patients.

Characterization and registration of 3D ultrasound for use in permanent breast seed implant brachytherapy treatment planning

PurposePermanent breast seed implant (PBSI) brachytherapy is a novel technique for early-stage breast cancer. Computed tomography (CT) images are used for treatment planning and freehand 2D ultrasound for implant guidance. The multimodality imaging approach leads to discrepancies in target identification. To address this, a prototype 3D ultrasound (3DUS) system was recently developed for PBSI. In this study, we characterize the 3DUS system performance, establish QA baselines, and develop and test a method to register 3DUS images to CT images for PBSI planning. Methods and Materials3DUS system performance was characterized by testing distance and volume measurement accuracy, and needle template alignment accuracy. 3DUS-CT registration was achieved through point-based registration using a 3D-printed model designed and constructed to provide visible landmarks on both images and tested on an in-house made gel breast phantom. ResultsThe 3DUS system mean distance measurement accuracy was within 1% in axial, lateral, and elevational directions. A volumetric error of 3% was observed. The mean needle template alignment error was 1.0° ± 0.3 ° and 1.3 ± 0.5 mm. The mean 3DUS-CT registration error was within 3 mm when imaging at the breast centre or across all breast quadrants. ConclusionsThis study provided baseline data to characterize the performance of a prototype 3DUS system for PBSI planning and developed and tested a method to obtain accurate 3DUS-CT image registration for PBSI planning. Future work will focus on system validation and characterization in a clinical context as well as the assessment of impact on treatment plans.

Geometrically variable three-dimensional ultrasound for mechanically assisted image-guided therapy of focal liver cancer tumors.

Image-guided focal ablation procedures are first-line therapy options in the treatment of liver cancer tumors that provide advantageous reductions in patient recovery times and complication rates relative to open surgery. However, extensive physician training is required and image guidance variabilities during freehand therapy applicator placement limit the sufficiency of ablation volumes and the overall potential of these procedures. We propose the use of three-dimensional ultrasound (3D US) to provide guidance and localization of therapy applicators, augmenting current ablation therapies without the need for specialized procedure suites. We have developed a novel scanning mechanism for geometrically variable 3D US images, a mechanical tracking system, and a needle applicator insertion workflow using a custom needle applicator guide for targeted image-guided procedures. A three-motor scanner was designed to use any commercially available US probe to generate accurate, consistent, and geometrically variable 3D US images. The designed scanner was mounted on a counterbalanced stabilizing and mechanical tracking system for determining the US probe orientation, which was assessed using optical tracking. Further exploiting the utility of the motorized scanner, an image-guidance workflow was developed that moved the probe to any identified target within an acquired 3D US image. The complete 3D US guidance system was used to perform mock targeted interventional procedures on a phantom by selecting a target in a 3D US image, navigating to the target, and performing needle insertion using a custom 3D-printed needle applicator guide. Registered postinsertion 3D US images and cone-beam computed tomography (CBCT) images were used to evaluate tip targeting errors when using the motors, tracking system, or mixed navigation approaches. Two 3D US image geometries were investigated to assess the accuracy of a small-footprint tilt approach and a large field-of-view hybrid approach for a total of 48 targeted needle insertions. 3D US image quality was evaluated in a healthy volunteer and compared to a commercially available matrix array US probe. A mean positioning error of 1.85±1.33mm was observed when performing compound joint manipulations with the mechanical tracking system. A combined approach for navigation that incorporated the motorized movement and the in-plane tracking system corrections performed the best with a mean tip error of 3.77±2.27mm and 4.27±2.47mm based on 3D US and CBCT images, respectively. No significant differences were observed between hybrid and tilt image acquisition geometries with all mean registration errors ≤1.2mm. 3D US volunteer images resulted in clear reconstruction of clinically relevant anatomy. A mechanically tracked system with geometrically variable 3D US provides a utility that enables enhanced applicator guidance, placement verification, and improved clinical workflow during focal liver tumor ablation procedures. Evaluations of the tracking accuracy, targeting capabilities, and clinical imaging feasibility of the proposed 3D US system, provided evidence for clinical translation. This system could provide a workflow for improving applicator placement and reducing local cancer recurrence during interventional procedures treating liver cancer and has the potential to be expanded to other abdominal interventions and procedures.

Development and Evaluation of CT-to-3D Ultrasound Image Registration Algorithm in Vertebral Phantoms for Spine Surgery.

Posterior spinal fusion surgery requires careful insertion of screws into the spine to avoid neurologic injury. While current systems use CT-scans, three-dimensional ultrasound (3DUS) could provide guidance by reconstructing the vertebral surface, and then registering a pre-operative vertebral model to that surface for localization. The aim of this study was to evaluate the accuracy and processing time of a custom CT-3DUS registration algorithm. A phantom human vertebra was 3D-printed and scanned with a motion capture-based 3D ultrasound (3DUS) system. Image registration was performed that included a pre-alignment phase using vertebral symmetry information, and then comparing Gaussian pyramid intensity-based registration with iterative-closest-point registration for final transformations. Image registration was performed 192 times while surgical registration between CT and real-world position was performed 84 times. The accuracy of image registration (CT-to-3DUS) was 0.3 ± 0.2mm and 0.9 ± 0.8° completed in 13.3 ± 2.9s. The surgical navigation accuracy (CT model to real-world position) of the system was 1.2 ± 0.5mm and 2.2 ± 2.0° completed in 16.2 ± 3.0s. Both meet accuracy thresholds of < 2mm and < 5° required for the surgery. A feasibility study on porcine spine qualitatively showed appropriate overlapping anatomy in CT-3DUS registrations. The usage of 3D ultrasound for navigation has demonstrated accuracy to provide radiation-free image guidance for spine surgery.

Positional and Orientational Accuracy of 3-D Ultrasound Navigation System on Vertebral Phantom Study

Adolescent idiopathic scoliosis (AIS) is a 3-D spinal deformity that affects 1%–3% of youth. Severe cases require surgical intervention involving the insertion of pedicle screws near the spinal cord, making accurate placement imperative. Currently, surgeons use either CT-navigation methods to guide the placement of screws or free-hand methods. The free-hand method has higher breach rates; however, CT-navigation exposes children to sensitive ionizing radiation. A novel custom 3-D ultrasound (3DUS) system has been developed to provide accuracy benefits similar to traditional CT-navigation systems without exposing patients to ionizing radiation. This study evaluates the accuracy of the custom 3DUS guidance system for localizing 3-D reconstructions of vertebral phantoms and tracking handheld surgical tools in the surgical space. Tool tracking was evaluated with commercial motion tracking cameras using a 3-D-printed pointer device and a high-precision probe device. Experiments were performed on 3-D-printed vertebral phantoms to investigate the positional and orientational accuracy using a high precision reference grid. The 3-D-printed pointer device was shown to be inferior to the high-precision probe, finding positional accuracy of 1.1 ± 1.1 mm versus 0.7 ± 0.4 mm. The rotational accuracy was 0.0° ± 1.7°, which met the surgical objective. The 3DUS localization, which was also evaluated using the vertebral phantoms and reference grid, showed positional accuracy of 0.8 ± 0.6 mm, making it a promising image-guidance tool for scoliosis surgery.

An ultrasound based platform for image-guided radiotherapy in canine bladder cancer patients.

Background and purposeUltrasound (US) is a non-invasive, non-radiographic imaging technique with high spatial and temporal resolution that can be used for localizing soft-tissue structures and tumors in real-time during radiotherapy (RT) (inter- and intra-fraction). A comprehensive approach incorporating an in-house 3D-US system within RT is presented. This system is easier to adopt into existing treatment protocols than current US based systems, with the aim of providing millimeter intra-fraction alignment errors and sensitivity to track intra-fraction bladder movement.Materials and methodsAn in-house integrated US manipulator and platform was designed to relate the computed tomographic (CT) scanner, 3D-US and linear accelerator coordinate systems. An agar-based phantom with measured speed of sound and densities consistent with tissues surrounding the bladder was rotated (0–45°) and translated (up to 55 mm) relative to the US and CT coordinate systems to validate this device. After acquiring and integrating CT and US images into the treatment planning system, US-to-US and US-to-CT images were co-registered to re-align the phantom relative to the linear accelerator.ResultsStatistical errors from US-to-US registrations for various patient orientations ranged from 0.1 to 1.7 mm for x, y, and z translation components, and 0.0–1.1° for rotational components. Statistical errors from US-to-CT registrations were 0.3–1.2 mm for the x, y and z translational components and 0.1–2.5° for the rotational components.ConclusionsAn ultrasound-based platform was designed, constructed and tested on a CT/US tissue-equivalent phantom to track bladder displacement with a statistical uncertainty to correct and track inter- and intra-fractional displacements of the bladder during radiation treatments.

A prospective blinded comparison of second trimester fetal measurements by expert and novice readers using low-cost novice-acquired 3D volumetric ultrasound

Rationale and objectives Two-dimensional (2D) ultrasound (US) is operator dependent, requiring operator skill and experience to selectively identify and record planes of interest for subsequent interpretation. This limits the utility of US in settings in which expert sonographers are unavailable. Three-dimensional (3D) US acquisition of an anatomic target, which enables reconstruction of any plane through the acquired volume, might reduce operator dependence by providing any desired image plane for interpretation, without identification of target planes of interest at the time of acquisition. We applied a low-cost 3DUS technology because of the wider potential application compared with dedicated 3DUS systems. We chose second trimester fetal biometric parameters for study because of their importance in maternal-fetal health globally. We hypothesized that expert and novice interpretations of novice-acquired 3D volumes would not differ from each other nor from expert measurements of expert-acquired 2D images, the clinical reference standard. Materials and methods This was a prospective, blinded, observational study. Expert sonographers blinded to 3DUS volumes acquired 2DUS images of second trimester fetuses from 32 subjects, and expert readers performed interpretation, during usual care. A novice sonographer blinded to other clinical data acquired oriented 3DUS image volumes of the same subjects on the same date. Expert readers blinded to other data assessed placental location (PL), fetal presentation (FP), and amniotic fluid volume (AFV) in novice-acquired 3D volumes. Novice and expert raters blinded to other data independently measured biparietal diameter (BPD), humerus length (HL), and femur length (FL) for each fetus from novice-acquired 3D volumes. Corresponding gestational age (GA) estimates were calculated. Inter-rater reliability of measurements and GAs (expert 3D versus expert 2D, novice 3D versus expert 2D, and expert 3D versus novice 3D) were assessed by intraclass correlation coefficient (ICC). Mean inter-rater measurement differences were analyzed using one-way ANOVA. Results 3D volume acquisition and reconstruction required mean 30.4 s (±5.7) and 70.0 s (±24.0), respectively. PL, FP, and AFV were evaluated from volumes for all subjects; mean time for evaluation was 16 s (±0.0). PL, FP, and AFV could be evaluated for all subjects. At least one biometric measurement was possible for 31 subjects (97%). Agreement between rater pairs for a composite of all measures was excellent (ICCs ≥ 0.95), and for individual measures was good to excellent (ICCs ≥ 0.75). Inter-rater differences were not significant (p > .05). Conclusions Expert and novice interpretations of novice-acquired 3DUS volumes of second trimester fetuses provided reliable biometric measures compared with expert interpretation of expert-acquired 2DUS images. 3DUS volume acquisition with a low-cost system may reduce operator dependence of ultrasound.

Development and Clinical Validation of a 3D Ultrasound System for Permanent Breast Seed Implant Brachytherapy

Permanent Breast Seed Implant (PBSI) is a novel form of breast brachytherapy completed in a single 1-2h procedure. PBSI planning uses CT simulation and treatment involves implanting Pd-103 seeds in and around the breast seroma via needles inserted through a template and guided by free-hand 2D ultrasound. The seroma shape and size vary from CT images to ultrasound and currently neither 3D images nor real-time guidance are available for PBSI. A 3D ultrasound (3DUS) system has been developed to fulfill these needs. This study extends this work to validate the 3DUS clinical implementation in PBSI planning and delivery procedure.

Three-dimensional surface and ultrasound imaging for daily IGRT of prostate cancer.

BackgroundImage guided radiotherapy (IGRT) is an essential pre-requisite for delivering high precision radiotherapy. We compared daily variation detected by two non-ionizing imaging modalities (surface imaging and trans-abdominal ultrasound, US) to verify prostate patient setup and internal organ variations.MethodsForty patients with organ confined prostate cancer and candidates to curative radiotherapy were enrolled in this prospective study. At each treatment session, after laser alignment, all patients received imaging by a 3D-surface and a 3D-US system. The shifts along the three directions (anterior-posterior AP, cranial-caudal CC, and later-lateral LL) were measured in terms of systematic and random errors. Then, we performed statistical analysis on the differences and the possible correlations between the two modalities.ResultsFor both IGRT modalities, surface imaging and US, 1318 acquisitions were collected. According with Shapiro Wilk test, the positioning error distributions were not Gaussian for both modalities.The differences between the systematic errors detected by the two modalities were statistically significant only in LL direction (p < 0.05), while the differences between the random errors were not statistically significant in any directions.The 95% confidence interval of the residual errors obtained by subtracting the random errors detected with surface images to those detected with US was included in the range from −7 mm to 7 mm corresponding to the minimum PTV margin adopted in AP direction in our clinical routine.ConclusionsFrom our data, it emerges that setup misalignments measured by surface imaging can be predictive of US displacements after the adjustment for systematic errors. Moreover, surface imaging can detect setup errors predictive of registration errors measured by US. This data suggest that the two IGRT modalities could be considered as complementary to each other and could represent a daily “low-cost” and non-invasive IGRT modality in prostate cancer patients.

Validation of a novel robot-assisted 3DUS system for real-time planning and guidance of breast interstitial HDR brachytherapy.

In current clinical practice, there is no integrated 3D ultrasound (3DUS) guidance system clinically available for breast brachytherapy. In this study, the authors present a novel robot-assisted 3DUS system for real-time planning and guidance of breast interstitial high dose rate (HDR) brachytherapy treatment. For this work, a new computer controlled robotic 3DUS system was built to perform a hybrid motion scan, which is a combination of a 6 cm linear translation with a 30° rotation at both ends. The new 3DUS scanner was designed to fit on a modified Kuske assembly, keeping the current template grid configuration but modifying the frame to allow the mounting of the 3DUS system at several positions. A finer grid was also tested. A user interface was developed to perform image reconstruction, semiautomatic segmentation of the surgical bed as well as catheter reconstruction and tracking. A 3D string phantom was used to validate the geometric accuracy of the reconstruction. The volumetric accuracy of the system was validated with phantoms using magnetic resonance imaging (MRI) and computed tomography (CT) images. In order to accurately determine whether 3DUS can effectively replace CT for treatment planning, the authors have compared the 3DUS catheter reconstruction to the one obtained from CT images. In addition, in agarose-based phantoms, an end-to-end procedure was performed by executing six independent complete procedures with both 14 and 16 catheters, and for both standard and finer Kuske grids. Finally, in phantoms, five end-to-end procedures were performed with the final CT planning for the validation of 3DUS preplanning. The 3DUS acquisition time is approximately 10 s. A paired Student t-test showed that there was no statistical significant difference between known and measured values of string separations in each direction. Both MRI and CT volume measurements were not statistically different from 3DUS volume (Student t-test: p > 0.05) and they were significantly correlated to 3DUS measurement (Pearson test: MRI p < 0.05 and CT p < 0.001). The mean angular separation distance between catheter trajectories segmented from 3DUS and CT images was 0.42° ± 0.24°, while the maximum and mean trajectory separations were 0.51 ± 0.19 and 0.37 ± 0.17 mm, respectively. Overall, the new finer grid has performed significantly better in terms of dosimetric indices. The planning target volume dosimetric indices were not found statistically different between 3DUS and CT planning (Student t-test, p > 0.05). Both the skin and the pectoral muscle dosimetric indices were within ABS guidelines. A novel robot-assisted 3DUS system was designed and validated. To their knowledge, this is the first system capable of performing real-time guidance and planning of breast multicatheter HDR brachytherapy treatments. Future investigation will test the feasibility of using the system in the clinic and for permanent breast brachytherapy.

Surface refraction of sound waves affects calibration of three-dimensional ultrasound.

BackgroundThree-dimensional ultrasound (3D-US) is used in planning and treatment during external beam radiotherapy. The accuracy of the technique depends not only on the achievable image quality in clinical routine, but also on technical limitations of achievable precision during calibration. Refraction of ultrasound waves is a known source for geometric distortion, but such an effect was not expected in homogenous calibration phantoms. However, in this paper we demonstrate that the discontinuity of the refraction index at the phantom surface may affect the calibration unless the ultrasound probe is perfectly perpendicular to the phantom.MethodsA calibration phantom was repeatedly scanned with a 3D-US system (Elekta Clarity) by three independent observers. The ultrasound probe was moved horizontally at a fixed angle in the sagittal plane. The resulting wedge shaped volume between probe and phantom was filled with water to couple in the ultrasound waves. Because the speed of sound in water was smaller than the speed of sound in Zerdine, the main component of the phantom, the angle of the ultrasound waves inside the phantom increased. This caused an apparent shift in the calibration features which was recorded as a function of the impeding angle. To confirm the magnitude and temperature dependence, the experiment was repeated by two of the observers with a mixture of ice and water at 0 °C and with thermalized tap water at 21 °C room temperature.ResultsDuring the first series of measurements, a linear dependency of the displacements dx of the calibration features on the angle α of the ultrasound probe was observed. The three observers recorded significantly nonzero (p < 0.0001) and very consistent slopes of dx/dα of 0.12, 0.12, and 0.13 mm/°, respectively..At 0 °C water temperature, the slope increased to 0.18 ± 0.04 mm/°. This matched the prediction of Snell’s law of 0.185 mm/° for a speed of sound of 1,402 m/s at the melting point of ice.At 21 °C, slopes of 0.11 and 0.12 mm/° were recorded in agreement with the first experiment at about room temperature. The difference to the theoretical expectation of 0.07 mm/° was not significant (p = 0.09).ConclusionsThe surface refraction of sound waves my affect the calibration of three-dimensional ultrasound. The temperature dependence of the effect rules out alternative explanations for the observed shifts in calibration. At room temperature and for a structure that is 10 cm below the water-phantom interface, a tilt of the ultrasound probe of 10° may result in a position reading that is off by more than half a millimeter. Such errors are of the order of other relevant errors typically encountered during the calibration of a 3D-US system. Hence, care must be taken not to tilt the ultrasound probe during calibration.

Towards real-time 3D ultrasound planning and personalized 3D printing for breast HDR brachytherapy treatment

Two different end-to-end procedures were tested for real-time planning in breast HDR brachytherapy treatment. Both methods are using a 3D ultrasound (3DUS) system and a freehand catheter optimization algorithm. They were found fast and efficient. We demonstrated a proof-of-concept approach for personalized real-time guidance and planning to breast HDR brachytherapy treatments.

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

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

A Novel Approach for Real-Time, Personalized Breast HDR Brachytherapy Treatment Using 3D Printing Technology

In breast interstitial high-dose-rate (HDR) brachytherapy, the number and positions of the catheters are usually chosen manually using a preimplant CT scan or fixed using 2D ultrasound, since real-time methodologies are non-existent. In this work, we present an innovative approach for real-time and personalized 3D ultrasound (3DUS) planning in breast HDR brachytherapy. Two different end-to-end procedures were tested for real-time planning. Both methods are using a computer controlled robotic 3DUS system for breast brachytherapy and a freehand catheter optimization algorithm; based on the open source Centroidal Voronoi Tessellations (CVT) algorithm and IPSA. The scanner is mounted on the Kuske template (Nucletron, an Elekta Company, Stockholm, Sweden) so that the scan direction is longitudinal to the catheter axis. The first method is using the Kuske template, meaning that the optimize catheter positions are snap to the available position within the template. The second method makes use of personalized templates built from a 3D printer using the results of the catheter optimization process. The new template fits on the Kuske assembly, however a new concept has emerged where personalized plates can be inserted in the middle of the template (Fig. 1a and 1b). This allows the user to keep the template in place and insert 3D printed personalized plates. The procedures were tested with 12, 14 and 16 catheters, three times each, in an agarose-based phantom with a hypo-echoic mass. The 3DUS acquisition time is less than 7s and the catheter optimization algorithm can obtain 10 complete treatments plans, with the corresponding dosimetric indices, in 90s. The catheter optimization algorithm was shown to enable reduction of the number of catheters to 12 without breaking ABS recommendations. It was also shown to be robust up to 3 mm implantation errors. The printing time of the two plates was approximately two hours. After the insertion procedure, dosimetric indices were still within RTOG guidelines down to 14 catheters for the Kuske method and down to 12 for the personalized template method. The method with the personalized template was significantly better (student t-test; p < 0.05) in terms of the cost function and PTV V100 as well as PTV D90. Fig. 1c and 1d are showing PTV V100 results compared to the optimal CVT optimization algorithm for the Kuske method (c) and for the personalized method (d). We have devised a simple, fast and efficient method for real-time and personalized 3DUS breast HDR brachytherapy treatment using inverse planning and 3D printing technology. This novel personalized approach could be easily extended to prostate and other sites.

A 3D ultrasound scanning system for image guided liver interventions

Two-dimensional ultrasound (2D US) imaging is commonly used for diagnostic and intraoperative guidance of interventional liver procedures; however, 2D US lacks volumetric information that may benefit interventional procedures. Over the past decade, three-dimensional ultrasound (3D US) has been developed to provide the missing spatial information. 3D US image acquisition is mainly based on mechanical, electromagnetic, and freehand tracking of conventional 2D US transducers, or 2D array transducers available on high-end machines. These approaches share many problems during clinical use for interventional liver imaging due to lack of flexibility and compatibility with interventional equipment, limited field-of-view (FOV), and significant capital cost compared to the benefits they introduce. In this paper, a novel system for mechanical 3D US scanning is introduced to address these issues. The authors have developed a handheld mechanical 3D US system that incorporates mechanical translation and tilt sector sweeping of any standard 2D US transducer to acquire 3D images. Each mechanical scanning function can be operated independently or may be combined to allow for a hybrid wide FOV acquisition. The hybrid motion mode facilitates registration of other modalities (e.g., CT or MRI) to the intraoperative 3D US images by providing a larger FOV in which to acquire anatomical information. The tilting mechanism of the developed mover allows image acquisition in the intercostal rib space to avoid acoustic shadowing from bone. The geometric and volumetric scanning validity of the 3D US system was evaluated on tissue mimicking US phantoms for different modes of operation. Identical experiments were performed on a commercially available 3D US system for direct comparison. To replicate a clinical scenario, the authors evaluated their 3D US system by comparing it to CT for measurement of angle and distance between interventional needles in different configurations, similar to those used for percutaneous ablation of liver tumors. The mean geometrical hybrid 3D reconstruction error measured from scanning of a known string phantom was less than 1 mm in two directions and 2.5 mm in the scanning direction, which was comparable or better than the same measurements obtained from a commercially available 3D US system. The error in volume measurements of spherical phantom models depended on depth of the object. For a 20 cm(3) model at a depth of 15 cm, a standard depth for liver imaging, the mean error was 3.6% ± 4.5% comparable to the 2.3% ± 1.8% error for the 3D US commercial system. The error in 3D US measurement of the tip distance and angle between two microwave ablation antennas inserted into the phantom was 0.9 ± 0.5 mm and 1.1° ± 0.7°, respectively. A 3D US system with hybrid scanning motions for large field-of-view 3D abdominal imaging has been developed and validated. The superior spatial information provided by 3D US might enhance image-guidance for percutaneous interventional treatment of liver malignancies. The system has potential to be integrated with other liver procedures and has application in other abdominal organs such as kidneys, spleen, or adrenals.

MO‐F‐144‐03: Real‐Time Guidance and Planning in Breast High Dose Rate Brachytherapy Using 3D Ultrasound

Purpose: In breast interstitial high dose rate (HDR) brachytherapy, the number and positions of the catheters are usually chosen manually using a preimplant CT scan. In this work, we present an innovative approach for real‐time 3D ultrasound (3DUS) planning in breast HDR brachytherapy. Methods: The end‐to‐end procedure was realized with a computer controlled robotic 3DUS system for breast brachytherapy so that both planning and guidance are possible. The scanner is mounted on the Kuske template (Nucletron, Veneendal, The Netherlands) so that the scan direction is longitudinal to the catheter axis. Software modules were developed for the acquisition and reconstruction of ultrasound images. A semi‐automatic segmentation algorithm and a needle reconstruction algorithm were integrated into the software to segment the planning target volume and reconstruct the catheter. A Centroidal Voronoi Tessellations (CVT) algorithm, in conjunction with IPSA, was used for catheter number and position optimization. The procedure was tested with 9 catheters in an agarose‐based phantom with a hypo‐echoic mass. Results: The 3DUS acquisition time is less than 7s and the catheter optimization algorithm can obtain 10 complete treatments plans, with the corresponding dosimetric indices, in 90s. The catheter optimization algorithm was shown to reduce the number of catheters to 12 without reducing the quality of the treatment. Breast PTV V100 and dose homogeneity index (DHI) calculated after the procedure were compared to the value obtained from the optimal plan calculated with the CVT algorithm. Both dosimetric indexes were still within RTOG guidelines after the procedure. However, the PTV V100 is smaller after the procedure due to the template‐based implantation. Isodoses are comparable. Conclusion: We have devised a simple, fast and efficient method for real‐time 3DUS guidance of breast HDR brachytherapy. This approach could be coupled with personalized 3D‐printed or robotic template to further optimize this brachytherapy procedure. Funding support: CIHR and NSERC

Contemporary technique of intraoperative 3-dimensional ultrasonography–guided transperineal prostate cryotherapy

Successful cryotherapy of the prostate for neoplasms relies on imaging to achieve good oncological outcomes with minimal complications. Traditional prostatic cryotherapy relies on 2-dimensional ultrasonography (2DUS) guidance, which often makes it difficult to track the passage of needles in an oblique plane. We describe our initial 3-dimensional ultrasonography (3DUS) system, and the subsequent improvements that have been made during the last 10 years. Our imaging system uses a Philips HDI 5000 ultrasonography unit, a standard PC, a Matrox Meteor II video frame grabber and 3DUS developed at Robarts Research Institute. For the cryotherapy we use ultrathin (17-gauge) IceRod needles. After image acquisition, preplanning is performed using the 3-dimensional (3D) software, and then the IceRod needles are inserted into the prostate. As the freezing process commences, continuous 3DUS images are taken and analyzed during the double freeze-thaw cycles to monitor the progress of the ice ball formation. Real-time intraoperative 3D imaging of the prostate during cryotherapy has allowed us to accurately preplan and then monitor the progression of ice ball formation, which represents a significant advantage over conventional 2DUS.