Donal B. Downey

RESULTS OF SALVAGE CRYOABLATION OF THE PROSTATE AFTER RADIATION: IDENTIFYING PREDICTORS OF TREATMENT FAILURE AND COMPLICATIONS

PURPOSEnWe conduct a critical evaluation of cryoablation of prostate cancer after failure of full dose radiotherapy to identify predictors of treatment failure and complications.nnnMATERIALS AND METHODSnA total of 125 cryoablation procedures were performed in 118 patients with proved local recurrence after full dose radiotherapy. Followup includes serial prostate specific antigen (PSA) and biopsy at 6,12 and 24 months. Kaplan-Meier plots were constructed for different PSA cutoffs. We separately analyzed different cohorts based on T stage, Gleason score, PSA before cryoablation and endocrine therapy status.nnnRESULTSnOf the 118 patients 114 had serum PSA nadir less than 0.5 ng./ml. Median followup was 18.6 months (range 3 to 54). Of the biopsy cores 3.1% (23 of 745) from 7 patients contained persistent viable cancer. Kaplan-Meier plots showed patients free of histological failure leveling at 87% and free from biochemical failure at 68%, 55% and 34%, respectively, with PSA greater than 4, 2 and 0.5 ng./ml. PSA greater than 10 ng./ml. before cryoablation, Gleason score 8 or greater before radiation and stage T3/T4 disease appeared to predict an unfavorable biochemical outcome. Serious complications included 4 rectourethral fistulas (3.3%) and severe incontinence (6.7%). Strong predictors of complications included bulky disease for fistulas and prior transurethral surgery.nnnCONCLUSIONSnSalvage cryoablation after radiation can achieve reasonable biochemical and histological results with acceptable morbidity. Cryoablation appears to be a reasonable treatment option for this patient population with few viable therapeutic options, provided vigorous patient selection criteria are adhered to.

Intra- and inter-observer variability and reliability of prostate volume measurement via two-dimensional and three-dimensional ultrasound imaging

We describe the results of a study to evaluate the intra- and inter-observer variability and reliability of prostate volume measurements made from transrectal ultrasound (TRUS) images, using either the (optimal) height-width-length (HWL) method (V = pi/6 HWL) with two-dimensional (2D) TRUS images (obtained as cross-sections of three-dimensional [3D] TRUS images) or manual planimetry of 3D TRUS images (the 3D US method). In this study, eight observers measured 15 prostate images, twice via each method, and an analysis of variance (ANOVA) was performed. This analysis shows that, with the 3D US method, intra-observer prostate volume estimates have 5.1% variability and 99% reliability, and inter-observer estimates have 11.4% variability and 96% reliability. With the HWL method, intra-observer estimates have 15.5% variability and 93% reliability, and inter-observer estimates have 21.9% variability and 87% reliability. Thus, in vivo prostate volume estimates from manual planimetry of 3D TRUS images have much lower variability and higher reliability than HWL estimates from 2D TRUS images.

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.

Evaluation of voxel-based registration of 3-D power Doppler ultrasound and 3-D magnetic resonance angiographic images of carotid arteries.

Spatial registration and fusion of ultrasound (US) images with other modalities may aid clinical interpretation. We implemented and evaluated on patient data an automated retrospective registration of magnetic resonance angiography (MRA) carotid bifurcation images with 3-D power Doppler ultrasound (PD US) and indirectly with 3-D B-mode US. Volumes were initially thresholded to reduce the uncorrelated noise signals. The registration algorithm subsequently maximized the mutual information measure between the PD US and 3-D MRA via iterative simplex search to find best rigid body transformation. We rated the performance of the algorithm visually on (n = 5) clinical MRA and 3-D PD US datasets. We also evaluated quantitatively the effect of thresholding, initial misalignment of the paired volumes and the reproducibility registration. We investigated the effect of image artefacts by simulation experiments. Preregistration misalignments of up to 5 mm in the transaxial plane, up to 10 mm along the axis of the carotids and up to 40 degrees resulted in 107 of 110 successful registrations, with translational and rotational errors of 0.32 mm +/- 0.3 mm and 1.6 +/- 2.1 degrees. The algorithm was not affected by missing arterial segments of up to 8 mm in length. The average registration time was 4 min. We conclude that the algorithm could be applied to 3-D US PD and MRA data for automated multimodality registration of carotid vessels without the use of fiducials.

THREE-DIMENSIONAL TRANSRECTAL ULTRASOUND GUIDED CRYOABLATION FOR LOCALIZED PROSTATE CANCER IN NONSURGICAL CANDIDATES: A FEASIBILITY STUDY AND REPORT OF EARLY RESULTS

PURPOSEnA 3-dimensional (D) transrectal ultrasound imaging system was incorporated into the cryoablation routine for prostate cancer to assess its feasibility and use. The objective was to improve visibility for probe placement and for intraoperative monitoring.nnnMATERIALS AND METHODSnA commercially available transrectal ultrasound unit was coupled with a custom designed software system to construct 3-dimensional prostate images. A total of 52 patients with clinically localized prostate cancer, in whom radiotherapy had failed (45) or who were otherwise judged to be nonsurgical candidates (7) were treated with cryoablation, using 3-D transrectal ultrasound for intraoperative guidance.nnnRESULTSnIn all cases the intraoperative 3-D transrectal ultrasound images provided a unique coronal view of the prostate, revealing useful information and facilitating more precise probe placement and treatment monitoring. Early postoperative histological and biochemical results and complication rates compare well with other contemporary series.nnnCONCLUSIONSnAlthough the precise role of cryoablation in the management of prostate cancer remains unclear and long-term results are pending, incorporation of a 3-D transrectal ultrasound imaging system into the cryoablation routine proved to be feasible and appeared to be a worthwhile effort to facilitate the procedure, and deserves further evaluation.

Three-dimensional ultrasound-guided core needle breast biopsy

A new core needle breast biopsy system guided by 3-D ultrasound (US) is proposed. Our device provides rapid imaging and real-time guidance, as well as breast stabilization and a needle guidance apparatus using 3-D imaging. The targeting accuracy of our device was tested by inserting a 14-gauge biopsy needle into agar phantoms under 3-D US guidance. A total of 18 0.8-mm stainless-steel beads embedded in the phantoms defined each of the four target positions tested. Positioning accuracy was calculated by comparing needle tip position to the preinsertion bead position, as measured by three observers three times each on 3-D US. The interobserver standard error of measurement was no more than 0.14 mm for the beads and 0.27 mm for the needle tips. A 3-D principal component analysis was performed to obtain the population distribution of needle tip position relative to the target beads for the four target positions. The 3-D 95% confidence intervals were found to have total widths ranging from 0.43 to 1.71 mm, depending on direction and bead position.

An algorithm for automatic needle localization in ultrasound-guided breast biopsies.

An algorithm was developed in order to reduce operator dependence in ultrasound-guided breast biopsy, by automatically locating the needle in the ultrasound image, and displaying its location on the image for the user. Ultrasound images of a typical breast biopsy needle inserted in a tissue-mimicking agar were obtained to test the algorithm. The resulting images were examined by a group of observers who recorded the values of the angle, intercept and tip coordinates of the needle in the image, and inter- and intra-observer variability studies were performed on the results. The results of the algorithm segmentation were compared to the values recorded by the observers, and physical measurements recorded at the time the images were acquired. The algorithm segmentation was precise enough to successfully (when considering angle and tip segmentation) target 90% of tumors of 4.5 mm in diameter situated at the center of the image.

Prospective Evaluation of the Role of Quantitative Doppler Ultrasound Surveillance in Liver Transplantation

Doppler ultrasound (DUS) is able to measure parameters of blood flow within vessels of transplanted organs, and vascular complications are associated with abnormal values. We analyzed the findings of 51 consecutive patients who underwent DUS on 2 occasions in the first postoperative week following liver transplantation for cirrhosis to determine the range of values in patients following liver transplantation. Three patients developed early vascular thromboses that were detected by the absence of a Doppler signal. In patients making an uneventful recovery, the arterial velocity tended to increase and the resistive index (RI) to decrease during the first postoperative week. All recipients were shown to have high‐velocity segments within the hepatic artery, without an increase in flow resistance. Assessment of the portal vein revealed narrowing at the anastomosis, associated with a segmental doubling of flow velocity, and the mean portal venous flow decreased by approximately 20% in the first postoperative week. In conclusion, a wide range of abnormalities occurs in the vessels of liver transplant recipients, which were not associated with the development of vascular complications or affect patient management. (Liver Transpl 2004;10:1183–1188.)

The development and evaluation of a three-dimensional ultrasound-guided breast biopsy apparatus☆

We have designed a prototype three-dimensional ultrasound guidance (3D USB) apparatus to improve the breast biopsy procedure. Features from stereotactic mammography and free-hand US-guided biopsy have been combined with 3D US imaging. This breast biopsy apparatus accurately guides a needle into position for the sampling of target tissue. We have evaluated this apparatus in three stages. First, by testing the placement accuracy of a needle in a tissue mimicking phantom. Second, with tissue mimicking phantoms that had embedded lesions for biopsy. Finally, by comparison to free-hand US-guided biopsy, using chicken breast phantoms. The first two stages of evaluation quantified the mechanical biases in the 3D USB apparatus. Compensating for these, a 96% success rate in targeting 3.2 mm lesions in chicken breast phantoms was achieved when using the 3D USB apparatus. The expert radiologists performing biopsies with free-hand US guidance achieved a 94.5% success rate. This has proven an equivalence between our apparatus, operated by non-experts, and free-hand biopsy performed by expert radiologists, for 3.2 mm lesions in vitro, with a 95% confidence.

Segmentation of carotid artery in ultrasound images

Segmentation of carotid artery lumen in 2D and 3D ultrasonography is an important step in evaluating arterial disease severity and finding vulnerable artherosclerotic plaques susceptible to rupture causing stroke. Because of the complexity of anatomical structures, noise as well as the requirement of accurate segmentation, interactions are necessary between observers and computer segmentation process. We describe a segmentation algorithm based on a discrete dynamic model approach with only one seed point to guide the initialization of the deformable model for each lumen cross-section. With one seed, the initial contour of the deformable model is generated using the entropy map of the original image and mathematical morphology operations. The deformable model is driven to fit the lumen contour by an internal force and an external force that are calculated respectively with geometrical properties of deformed contour and with the image gray level features. We also introduce a set of metrics based on a contour probability distribution function for evaluating the accuracy and variability of the interactive segmentation algorithm. These metrics provide a complete performance evaluation of an interactive segmentation algorithm and a means for comparing different algorithm settings. Seven images of the common, internal and external carotid arteries were chosen to test the segmentation algorithm. The average position error and average variability of the boundary segmentation result are 0.2 mm and 0.25 mm.