Minimally invasive focal ablation of liver cancer is an alternative technique to conventional methods for early-stage tumors. Sufficient therapy is provided when ablation applicators are placed at their intended target locations, but current practices are occasionally unable to achieve the required degree of accuracy, as observed by local cancer recurrence rates. We have developed a mechanically assisted 3D ultrasound (US) imaging and guidance system capable of providing geometrically variable images to increase intraoperative spatial information and propose a new method for placing therapeutic applicators during focal liver tumor ablations. A three-motor mechanical mover was designed to provide linear, tilt, and combined hybrid geometries for user-defined 3D US fields-of-view. This mover can manipulate any clinically available 2D US transducer mounted in a transducer-specific 3D-printed holders and is held by a counterbalanced mechanical guidance system, which contains electromagnetic brakes and encoders to track the position of the transducer. Fabrication of a transducer-specific needle guide allowed for information from 3D US images and targets to be overlaid with live 2D US to perform an image-guided workflow. End-to-end testing from 3D US acquisition to needle insertion was performed with a mock phantom procedure to assess overall needle placement accuracy and a potential clinical workflow. Mean applicator placement error was 3.8 ± 1.9 mm for all trials and demonstrated that our 3D US image-guided system may be a feasible approach for guiding ablation applicators accurately during focal liver tumor ablation procedures.
Image-guided biopsy is crucial for diagnosis, staging, and treatment planning of women with breast cancer. Conventional imaging modalities to guide breast biopsy are not optimal, often resulting in inconclusive or false-negative diagnosis. High-resolution breast-specific functional imaging using positron emission mammography (PEM) has demonstrated increased sensitivity and diagnostic accuracy for detecting breast tumours compared to conventional modalities. PEM shows potential to be an optimal method for tumour detection, but anatomical reference and visualization for needle guidance are not available for guiding biopsy. This paper reports on the development of a mechatronic guidance system designed for integration with an advanced PEM system and ultrasound (US) to improve sampling accuracy during imageguided breast biopsy. The system contains a mechatronic guidance arm and biopsy device, with an integrated US transducer and core-needle biopsy gun. Custom software modules were developed for 3D needle tracking and user guidance. To validate and demonstrate the utility of its system components, the mechatronic guidance arm and biopsy device were assessed using a simulated PEM detector plate. Registration to the simulated detector plate and validation demonstrates accurate needle tracking with a mean Target Registration Error <1mm. Biopsy accuracy was evaluated under ideal detection and mechatronic guidance conditions using tissue-mimicking breast phantoms, allowing targets <1mm to be sampled within 95% confidence. Our results show feasibility for the mechatronic guidance system to be integrated with PEM and US for accurate image-guided breast biopsy. Current work focuses on evaluating the complete mechatronic system ability to accurately guide, target, and biopsy simulated breast lesions.
KEYWORDS: 3D image processing, 3D acquisition, Computed tomography, Visualization, Tumors, Ultrasonography, Image visualization, 3D image reconstruction, High dynamic range imaging, Imaging systems
Brachytherapy, a type of radiotherapy, may be used to place radioactive sources into or in close proximity to tumors, providing a method for conformally escalating dose in the tumor and the local area surrounding the malignancy. High-dose-rate interstitial brachytherapy of vaginal tumors requires precise placement of multiple needles through holes in a plastic perineal template to deliver treatment while optimizing dose and avoiding overexposure of nearby organs at risk (OARs). Despite the importance of needle placement, image guidance for adaptive, intraoperative needle visualization, allowing misdirected needles to be identified and corrected during insertion, is not standard practice. We have developed a 360-deg three-dimensional (3-D) transvaginal ultrasound (TVUS) system using a conventional probe with a template-compatible custom sonolucent vaginal cylinder and propose its use for intraoperative needle guidance during interstitial gynecologic brachytherapy. We describe the 3-D TVUS mechanism and geometric validation, present mock phantom procedure results, and report on needle localization accuracy in patients. For the six patients imaged, landmark anatomical features and all needles were clearly visible. The implementation of 360-deg 3-D TVUS through a sonolucent vaginal cylinder provides a technique for visualizing needles and OARs intraoperatively during interstitial gynecologic brachytherapy, enabling implants to be assessed and providing the potential for image guidance.
Liver cancer is the second and sixth most frequent cause of cancer mortality worldwide in men and women, respectively, with high prevalence in under developed and developing countries. Minimally invasive focal ablation of liver tumors is an alternative technique to resection and transplantation for early-stage cancer and is focused on reducing patient complications and recovery times. Although promising, the therapeutic benefits are currently present with high local cancer recurrence. One potential source of error arises when performing therapy applicator guidance with 2D ultrasound (US) since the field-of-view is limited and requires the physician to build a mental image of the anatomy. Our solution to this limitation has been the development of a novel mechanically assisted 3D US imaging and guidance system capable of providing geometrically variable images. A three-motor mechanical mover was designed to provide linear, tilt, and hybrid geometries with adjustable ranges of motion for variable 3D US fields-of-view. This mover can manipulate any clinically available 2D US transducer via transducer-specific 3D-printed holders to guide applicator insertions intraoperatively. This mover is held by a counterbalanced mechanical “arm and wrist”, which contain electromagnetic brakes and five encoders to track the position of the transducer. This mechanical support is mounted on a portable cart with coarse adjustable height to accommodate gross differences in patient sizes. This work represents the design, construction, software implementation, preliminary 3D volume reconstruction evaluation, and the first qualitative human volunteer scans. Geometric errors performed on a grid phantom were <3% and human volunteer images were clinically applicable.
During high-dose-rate (HDR) interstitial brachytherapy of gynecologic malignancies, precise placement of multiple needles is necessary to provide optimal dose to the tumor while avoiding overexposing nearby healthy organs, such as the bladder and rectum. Needles are currently placed based on preoperative imaging and clinical examination but there is currently no standard for intraoperative image guidance. We propose the use of a three-dimensional (3D) ultrasound (US) system incorporating three scanning geometries: 3D transrectal US (TRUS), 360° 3D sidefire transvaginal US (TVUS), and 3D endfire TVUS, to provide an accessible and versatile tool for intraoperative image guidance during interstitial gynecologic brachytherapy. Images are generated in 12 - 20 s by rotating a conventional two-dimensional US probe, providing a reconstructed 3D image immediately following acquisition. Studies of needles in patient images show mean differences in needle positions of 3.82 ± 1.86 mm and 2.36 ± 0.97 mm in TRUS and sidefire TVUS, respectively, when compared to the clinical x-ray computed tomography (CT) images. A proof-of-concept phantom study of the endfire TVUS mode demonstrated a mean positional difference of 1.91 ± 0.24 mm. Additionally, an automatic needle segmentation tool was tested on a 360° 3D TVUS patient image resulting in a mean angular difference of 0.44 ± 0.19 ° and mean positional difference of 0.78 ± 0.17 mm when compared to manually segmented needles. The implementation of 3D US image guidance during HDR interstitial gynecologic brachytherapy provides a versatile intraoperative system with the potential for improved implant quality and reduced risk to nearby organs.
In high-dose-rate (HDR) interstitial gynecologic brachytherapy, needles are positioned into the tumor and surrounding area through a template to deliver radiotherapy. Optimal dose and avoidance of nearby organs requires precise needle placement; however, there is currently no standard method for intra-operative needle visualization or guidance. We have developed and validated a 360° three-dimensional (3D) transvaginal ultrasound (TVUS) system and created a sonolucent vaginal cylinder that is compatible with the current template to accommodate a conventional side-fire ultrasound probe. This probe is rotated inside the hollow sonolucent cylinder to generate a 3D image. We propose the use of this device for intra-operative verification of brachytherapy needle locations. In a feasibility study, the first ever 360° 3D TVUS image of a gynecologic brachytherapy patient was acquired and the image allowed key features, including bladder, rectum, vaginal wall, and bowel, to be visualized with needles clearly identifiable. Three patients were then imaged following needle insertion (28 needles total) and positions of the needles in the 3D TVUS image were compared to the clinical x-ray computed tomography (CT) image, yielding a mean trajectory difference of 1.67 ± 0.75°. The first and last visible points on each needle were selected in each modality and compared; the point pair with the larger distance was selected as the maximum difference in needle position with a mean maximum difference of 2.33 ± 0.78 mm. This study demonstrates that 360° 3D TVUS may be a feasible approach for intra-operative needle localization during HDR interstitial brachytherapy of gynecologic malignancies.
Proc. SPIE. 9036, Medical Imaging 2014: Image-Guided Procedures, Robotic Interventions, and Modeling
KEYWORDS: 3D image processing, Tumors, Computed tomography, Ultrasonography, Liver, 3D metrology, 3D acquisition, 3D modeling, Radiofrequency ablation, Microwave radiation
Image-guided percutaneous ablation is the standard treatment for focal liver tumors deemed inoperable and is commonly
used to maintain eligibility for patients on transplant waitlists. Radiofrequency (RFA), microwave (MWA) and cryoablation
technologies are all delivered via one or a number of needle-shaped probes inserted directly into the tumor.
Planning is mostly based on contrast CT/MRI. While intra-procedural CT is commonly used to confirm the intended
probe placement, 2D ultrasound (US) remains the main, and in some centers the only imaging modality used for needle
guidance. Corresponding intraoperative 2D US with planning and other intra-procedural imaging modalities is essential
for accurate needle placement. However, identification of matching features of interest among these images is often
challenging given the limited field-of-view (FOV) and low quality of 2D US images. We have developed a passive
tracking arm with a motorized scan-head and software tools to improve guiding capabilities of conventional US by large
FOV 3D US scans that provides more anatomical landmarks that can facilitate registration of US with both planning and
intra-procedural images. The tracker arm is used to scan the whole liver with a high geometrical accuracy that facilitates
multi-modality landmark based image registration. Software tools are provided to assist with the segmentation of the
ablation probes and tumors, find the 2D view that best shows the probe(s) from a 3D US image, and to identify the
corresponding image from planning CT scans. In this paper, evaluation results from laboratory testing and a phase 1
clinical trial for planning and guiding RFA and MWA procedures using the developed system will be presented. Early
clinical results show a comparable performance to intra-procedural CT that suggests 3D US as a cost-effective
alternative with no side-effects in centers where CT is not available.
Prostate biopsy is the clinical standard for prostate cancer diagnosis. To improve the accuracy of targeting suspicious
locations, systems have been developed that can plan and record biopsy locations in a 3D TRUS image acquired at the
beginning of the procedure. Some systems are designed for maximum compatibility with existing ultrasound equipment
and are thus designed around the use of a conventional 2D TRUS probe, using controlled axial rotation of this probe to
acquire a 3D TRUS reference image at the start of the biopsy procedure. Prostate motion during the biopsy procedure
causes misalignments between the prostate in the live 2D TRUS images and the pre-acquired 3D TRUS image. We
present an image-based rigid registration technique that aligns live 2D TRUS images, acquired immediately prior to
biopsy needle insertion, with the pre-acquired 3D TRUS image to compensate for this motion. Our method was
validated using 33 manually identified intrinsic fiducials in eight subjects and the target registration error was found to
be 1.89 mm. We analysed the suitability of two image similarity metrics (normalized cross correlation and mutual
information) for this task by plotting these metrics as a function of varying parameters in the six degree-of-freedom
transformation space, with the ground truth plane obtained from registration as the starting point for the parameter
exploration. We observed a generally convex behaviour of the similarity metrics. This encourages their use for this
registration problem, and could assist in the design of a tool for the detection of misalignment, which could trigger the
execution of a non-real-time registration, when needed during the procedure.
Prostate biopsy is the clinical standard for the definitive diagnosis of prostate cancer. To overcome the limitations of 2D
TRUS-guided biopsy systems when targeting pre-planned locations, systems have been developed with 3D guidance to
improve the accuracy of cancer detection. Prostate deformation due to needle insertion and biopsy gun firing is a
potential source of error that can cause target misalignments during biopsies. We use non-rigid registration of 2D TRUS
images to quantify the deformation during the needle insertion and the biopsy gun firing procedure, and compare this
effect in biopsies performed using a handheld TRUS probe with those performed using a mechanically assisted 3D
TRUS guided biopsy system. Although the mechanically assisted biopsy system had a mean deformation approximately
0.2 mm greater than that of the handheld approach, it yielded a lower relative increase of deformation near the needle
axis during the needle insertion stage and greater deformational stability of the prostate during the biopsy gun firing
stage. We also analyzed the axial and lateral components of the tissue motion; our results indicated that the motion is
weakly biased in the direction orthogonal to the needle, which is less than ideal from a targeting standpoint given the
long, narrow cylindrical shape of the biopsy core.
In order to obtain a definitive diagnosis of prostate cancer, over one million men undergo prostate biopsies every year.
Currently, biopsies are performed under two-dimensional (2D) transrectal ultrasound (TRUS) guidance with manual
stabilization of a hand-held end- or side-firing transducer probe. With this method, it is challenging to precisely guide a
needle to its target due to a potentially unstable ultrasound probe and limited anatomic information, and it is impossible
to obtain a 3D record of biopsy locations. We have developed a mechanically-stabilized, 3-dimensional (3D) TRUSguided
prostate biopsy system, which provides additional anatomic information and permits a 3D record of biopsies. A
critical step in this system's performance is the registration of 3D-TRUS images obtained during the procedure, which
compensates for intra-session motion and deformation of the prostate. We evaluated the accuracy and variability of
surface-based 3D-TRUS to 3D-TRUS rigid and non-rigid registration by measuring the target registration (TRE) error as
the post-registration misalignment of manually marked, corresponding, intrinsic fiducials. We also measured the fiducial
localization error (FLE), to measure its contribution to the TRE. Our results yielded mean TRE values of 2.13 mm and
2.09 mm for rigid and non-rigid techniques, respectively. Our FLE of 0.21 mm did not dominate the overall TRE. These
results compare favorably with a clinical need for a TRE of less than 2.5 mm.
Proc. SPIE. 7625, Medical Imaging 2010: Visualization, Image-Guided Procedures, and Modeling
KEYWORDS: Biopsy, Prostate, 3D acquisition, 3D image processing, 3D modeling, Ultrasonography, 3D displays, Transducers, Image segmentation, Imaging systems
Prostate biopsy procedures are currently limited to using 2D transrectal ultrasound (TRUS) imaging to guide the biopsy
needle. Being limited to 2D causes ambiguity in needle guidance and provides an insufficient record to allow guidance
to the same suspicious locations or avoid regions that are negative during previous biopsy sessions. We have developed
a mechanically assisted 3D ultrasound imaging and needle tracking system, which supports a commercially available
TRUS probe and integrated needle guide for prostate biopsy. The mechanical device is fixed to a cart and the
mechanical tracking linkage allows its joints to be manually manipulated while fully supporting the weight of the
ultrasound probe. The computer interface is provided in order to track the needle trajectory and display its path on a
corresponding 3D TRUS image, allowing the physician to aim the needle-guide at predefined targets within the prostate.
The system has been designed for use with several end-fired transducers that can be rotated about the longitudinal axis
of the probe in order to generate 3D image for 3D navigation. Using the system, 3D TRUS prostate images can be
generated in approximately 10 seconds. The system reduces most of the user variability from conventional hand-held
probes, which make them unsuitable for precision biopsy, while preserving some of the user familiarity and procedural
workflow. In this paper, we describe the 3D TRUS guided biopsy system and report on the initial clinical use of this
system for prostate biopsy.
Prostate biopsy procedures are generally limited to 2D transrectal ultrasound (TRUS) imaging for biopsy needle
guidance. This limitation results in needle position ambiguity and an insufficient record of biopsy core locations in cases
of prostate re-biopsy. We have developed a multi-jointed mechanical device that supports a commercially available
TRUS probe with an integrated needle guide for precision prostate biopsy. The device is fixed at the base, allowing the
joints to be manually manipulated while fully supporting its weight throughout its full range of motion. Means are
provided to track the needle trajectory and display this trajectory on a corresponding TRUS image. This allows the
physician to aim the needle-guide at predefined targets within the prostate, providing true 3D navigation. The tracker has
been designed for use with several end-fired transducers that can be rotated about the longitudinal axis of the probe to
generate 3D images. The tracker reduces the variability associated with conventional hand-held probes, while preserving
user familiarity and procedural workflow. In a prostate phantom, biopsy needles were guided to within 2 mm of their
targets, and the 3D location of the biopsy core was accurate to within 3 mm. The 3D navigation system is validated in
the presence of prostate motion in a preliminary patient study.
Ultrasound imaging has revolutionized the treatment of prostate cancer by producing increasingly accurate models
of the prostate and influencing sophisticated targeting procedures for the insertion of radioactive seeds during
brachytherapy. Three-dimensional (3D) ultrasound imaging, which allows 3D models of the prostate to be
constructed from a series of two-dimensional images, helps to accurately target and implant seeds into the prostate.
We have developed a compact robotic apparatus, as well as an effective method for guiding and controlling the
insertion of transperineal needles into the prostate. This device has been designed to accurately guide a needle in 3D
space so that the needle can be inserted into the prostate at an angle that does not interfere with the pubic arch. The
physician can adjust manually or automatically the position of the apparatus in order to place several radioactive
seeds into the prostate at designated target locations. Because many physicians are wary of conducting robotic
surgical procedures, the apparatus has been developed so that the physician can position the needle for manual
insertion and apply a method for manually releasing the needle without damaging the apparatus or endangering the
patient.
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