Biomedical subjects

Donal B Downey

Publications and source records attributed to Donal B Downey.

9 recordsLinked to original sources

PubMed2006

Needle and seed segmentation in intra-operative 3D ultrasound-guided prostate brachytherapy.

In order to guide the needle to the correct location in 3D US-guided brachytherapy, the needle is continuously tracked as it is being inserted. A pre-scan before the needle insertion and a post-scan after the needle insertion are subtracted to obtain a difference image containing the needle. The image is projected along two orthogonal directions approximately perpendicular to the needle, and the 3D needle is reconstructed from the segmented needles in the two projected images. The seeds implanted with the needle are located in the cropped volume along the needle. Thus, the seeds are segmented using a tri-bar model and 3D line segment patterns. Finally, the positions of the seeds are determined using a peak detection technique. Experiments with agar and turkey/chicken phantoms as well as patient data demonstrated that our needle segmentation technique could segment the needle in near real-time with an accuracy of 0.6 mm in position and 1.0 degrees in orientation. The true-positive rate for seed segmentation is 100% for the agar phantom and 93% for the chicken phantom. The average distance to manual seed segmentation was 1.0mm for the agar phantom and 1.7 mm for the chicken phantom.

Algorithms↗

PubMed2006

High-frequency ultrasound: a useful tool for evaluating the abdominal wall following free TRAM and DIEP flap surgery.

BACKGROUND: This is the first study to use a standardized ultrasound protocol to evaluate hernia and abdominal wall laxity following free transverse rectus abdominis myocutaneous (TRAM) and deep inferior epigastric perforator (DIEP) flap surgery. METHODS: All patients who underwent free TRAM and DIEP flap surgery performed by the senior author between the years 1994 and 2003 were recruited for physical examination and ultrasound of the abdominal wall for the dynamic evaluation of hernia and abdominal wall laxity. RESULTS: A total of 25 of 28 patients were followed up (89 percent). Eleven were in the DIEP flap group (44 percent) and 14 were in the free TRAM flap group (56 percent). Age- and body habitus-matched female volunteers (n = 12) were also used in this study. The mean follow-up was 3.8 years (range, 0.8 to 8.2 years). Although the kappa coefficient was +1 for detection of hernia on physical examination between two independent examiners, the interobserver correlation was poor for detection of bulges (kappa coefficient, +0.53). Ultrasound showed that abdominal wall laxity was statistically highest in the upright position, followed by 30 degrees of truncal flexion, and lowest in the supine position. The amount of abdominal wall laxity detected by ultrasound was significantly higher in the free TRAM flap group than in the free DIEP flap group. Two hernias were detected in the TRAM flap group by ultrasound and one hernia was previously known in the DIEP flap group. CONCLUSION: This is the first study to establish a standardized ultrasound protocol as an adjunct diagnostic tool to clinical examination for the dynamic evaluation of postoperative hernia and abdominal wall laxity.

Abdominal Wall↗

PubMed2006

Automated localization of implanted seeds in 3D TRUS images used for prostate brachytherapy.

An algorithm has been developed in this paper to localize implanted radioactive seeds in 3D ultrasound images for a dynamic intraoperative brachytherapy procedure. Segmentation of the seeds is difficult, due to their small size in relatively low quality of transrectal ultrasound (TRUS) images. In this paper, intraoperative seed segmentation in 3D TRUS images is achieved by performing a subtraction of the image before the needle has been inserted, and the image after the seeds have been implanted. The seeds are searched in a "local" space determined by the needle position and orientation information, which are obtained from a needle segmentation algorithm. To test this approach, 3D TRUS images of the agar and chicken tissue phantoms were obtained. Within these phantoms, dummy seeds were implanted. The seed locations determined by the seed segmentation algorithm were compared with those obtained from a volumetric cone-beam flat-panel micro-CT scanner and human observers. Evaluation of the algorithm showed that the rms error in determining the seed locations using the seed segmentation algorithm was 0.98 mm in agar phantoms and 1.02 mm in chicken phantoms.

Algorithms↗

PubMed2005

Brachytherapy needle deflection evaluation and correction.

In prostate brachytherapy, an 18-gauge needle is used to implant radioactive seeds. This thin needle can be deflected from the preplanned trajectory in the prostate, potentially resulting in a suboptimum dose pattern and at times requiring repeated needle insertion to achieve optimal dosimetry. In this paper, we report on the evaluation of brachytherapy needle deflection and bending in test phantoms and two approaches to overcome the problem. First we tested the relationship between needle deflection and insertion depth as well as whether needle bending occurred. Targeting accuracy was tested by inserting a brachytherapy needle to target 16 points in chicken tissue phantoms. By implanting dummy seeds into chicken tissue phantoms under 3D ultrasound guidance, the overall accuracy of seed implantation was determined. We evaluated methods to overcome brachytherapy needle deflection with three different insertion methods: constant orientation, constant rotation, and orientation reversal at half of the insertion depth. Our results showed that needle deflection is linear with needle insertion depth, and that no noticeable bending occurs with needle insertion into the tissue and agar phantoms. A 3D principal component analysis was performed to obtain the population distribution of needle tip and seed position relative to the target positions. Our results showed that with the constant orientation insertion method, the mean needle targeting error was 2.8 mm and the mean seed implantation error was 2.9 mm. Using the constant rotation and orientation reversal at half insertion depth methods, the deflection error was reduced. The mean needle targeting errors were 0.8 and 1.2 mm for the constant rotation and orientation reversal methods, respectively, and the seed implantation errors were 0.9 and 1.5 mm for constant rotation insertion and orientation reversal methods, respectively.

Agar↗

PubMed2005

Oblique needle segmentation and tracking for 3D TRUS guided prostate brachytherapy.

An algorithm was developed in order to segment and track brachytherapy needles inserted along oblique trajectories. Three-dimensional (3D) transrectal ultrasound (TRUS) images of the rigid rod simulating the needle inserted into the tissue-mimicking agar and chicken breast phantoms were obtained to test the accuracy of the algorithm under ideal conditions. Because the robot possesses high positioning and angulation accuracies, we used the robot as a "gold standard," and compared the results of algorithm segmentation to the values measured by the robot. Our testing results showed that the accuracy of the needle segmentation algorithm depends on the needle insertion distance into the 3D TRUS image and the angulations with respect to the TRUS transducer, e.g., at a 10 degrees insertion anglulation in agar phantoms, the error of the algorithm in determining the needle tip position was less than 1 mm when the insertion distance was greater than 15 mm. Near real-time needle tracking was achieved by scanning a small volume containing the needle. Our tests also showed that, the segmentation time was less than 60 ms, and the scanning time was less than 1.2 s, when the insertion distance into the 3D TRUS image was less than 55 mm. In our needle tracking tests in chicken breast phantoms, the errors in determining the needle orientation were less than 2 degrees in robot yaw and 0.7 degrees in robot pitch orientations, for up to 20 degrees needle insertion angles with the TRUS transducer in the horizontal plane when the needle insertion distance was greater than 15 mm.

Agar↗

PubMed2003

Serial histopathology results of salvage cryoablation for prostate cancer after radiation failure.

PURPOSE: There has been a paucity of long-term followup reports of cryoablation for prostate cancer. In particular, little is known regarding the long-term histological results following salvage cryoablation. We report serial biopsy results of up to 43 months on 106 patients who underwent cryoablation after radical radiotherapy failed. MATERIALS AND METHODS: A total of 110 cryoablation procedures were done in 106 patients for biopsy proven, clinically localized radiation failure. Postoperatively transrectal ultrasound guided biopsy (usually 4 cores) was done at approximately 3, and/or 6, 12 and 24 months, and thereafter as indicated by prostate specific antigen, which was measured every 6 months. RESULTS: Of 818 biopsy cores a total of 23 (2.8%) from 15 patients (14.2%) were positive. Of the positive cores 73.9% were found within year 1 following cryoablation. Residual viable prostate glands and stroma were found in 42.4% and 27.4% of patients, respectively, at various time points. The frequency of various histological features, the most common being necrosis and fibrosis, was tabulated from the serial biopsy histology reports. CONCLUSIONS: The results of serial biopsies have improved our understanding of the histopathological changes as well as the capabilities and limitations of salvage cryoablation. The biopsy positivity rate is acceptable, although the finding of persistent viable prostatic tissue in a substantial proportion of patients implies that vigilant long-term followup is mandatory.

Aged↗

PubMed2003

Semiautomatic three-dimensional segmentation of the prostate using two-dimensional ultrasound images.

In this paper, we report on two methods for semiautomatic three-dimensional (3-D) prostate boundary segmentation using 2-D ultrasound images. For each method, a 3-D ultrasound prostate image was sliced into the series of contiguous 2-D images, either in a parallel manner, with a uniform slice spacing of 1 mm, or in a rotational manner, about an axis approximately through the center of the prostate, with a uniform angular spacing of 5 degrees. The segmentation process was initiated by manually placing four points on the boundary of a selected slice, from which an initial prostate boundary was determined. This initial boundary was refined using the Discrete Dynamic Contour until it fit the actual prostate boundary. The remaining slices were then segmented by iteratively propagating this result to an adjacent slice and repeating the refinement, pausing the process when necessary to manually edit the boundary. The two methods were tested with six 3-D prostate images. The results showed that the parallel and rotational methods had mean editing rates of 20% and 14%, and mean (mean absolute) volume errors of -5.4% (6.5%) and -1.7% (3.1%), respectively. Based on these results, as well as the relative difficulty in editing, we conclude that the rotational segmentation method is superior.

Algorithms↗

PubMed2003

Training module to teach ultrasound-guided breast biopsy skills to residents improves accuracy.

OBJECTIVE: To evaluate the effectiveness of a training module in teaching residents the skills necessary to perform accurate and safe ultrasound-guided breast biopsies (USGBB). METHODS: Twelve residents with no USGBB experience, but variable ultrasound (US) experience, were randomly assigned to 2 groups; 1 group participated in a training module, and the other received no training. Each resident then attempted 30 core biopsies of "lesions" implanted in breast phantoms. Successful biopsies extracted some "lesion" material. "Chest wall" hits were also counted. RESULTS: The trained residents had significantly fewer "chest wall" hits than the untrained group (p < 0.002), but there was no significant difference in the number of successful biopsies (73% v. 43%, p = 0.09). The subgroup of residents who were USGBB trained but inexperienced in US (n = 4) achieved more successful biopsies (p < 0.05) and fewer "chest wall" hits (p < 0.01) than their matched untrained cohort (n = 3). The trained US-experienced subgroup (n = 2) had fewer "chest wall" hits than the matched untrained subgroup (n = 3; p < 0.05) but similar biopsy success rates. Untrained US-experienced residents (n = 3) had more successful biopsies than untrained US-inexperienced residents (n = 3; p < 0.001) and similar "chest wall" hits. CONCLUSION: Residents with training perform USGBBs more safely, and training significantly improves accuracy of USGBB in residents with no US experience. US experience improves biopsy success rates but does not affect safety levels of residents with no USGBB training.

Animals↗

PubMed2002

Comparison of core needle breast biopsy techniques: freehand versus three-dimensional US guidance.

RATIONALE AND OBJECTIVES: No single method is generally accepted for evaluating the accuracy of breast biopsy techniques before their clinical implementation. The purpose of this study was to test a new process for evaluating biopsy techniques by using it in the evaluation of a prototype three-dimensional ultrasound (US)-guided biopsy device. MATERIALS AND METHODS: The biopsy accuracy of a new three-dimensional US-guided breast biopsy device was compared to that of the accepted clinical practice of biopsy by expert radiologists with two-dimensional freehand US guidance. Biopsies were performed in chicken tissue phantoms containing 3.2-mm lesions made of poly(vinyl alcohol) cryogel. The criterion for a successful biopsy was the presence of lesion in the sample. The equivalence limit difference tested was 10% by using a power of 90% and a two-sided test significance level, a, of 10%. RESULTS: The biopsy success rate of the three-dimensional US-guided system (96%) was equivalent to that of expert radiologists using two-dimensional freehand US guidance (94.5%) in tissue phantoms containing poly(vinyl alcohol) cryogel lesions. CONCLUSION: This evaluation procedure is a valuable precursor to clinical trials in the assessment of biopsy techniques. The three-dimensional US-guided breast biopsy system provides a suitable alternative to two-dimensional freehand US guidance for biopsy of breast cancer.

Animals↗