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Biomedical subjects

D B Downey

Publications and source records attributed to D B Downey.

At least 19 recordsLinked to original sources
PubMed2004

3D ultrasound guided breast biopsy system.

Stereotactic X-ray mammography (SM) and ultrasound (US) guidance are commonly used techniques for breast biopsy. While SM provides 3D targeting information and US provides real-time guidance, both techniques have limitations. SM is a long and uncomfortable procedure and the US guided procedure is inherently 2D, requiring a skilled physician for both safety and accuracy. We have developed a 3D US-guided biopsy system to integrate with SM. The dual modality breast biopsy system combines the advantages of both approaches with 3D US and SM targeting, near real-time 3D and real-time 2D US guidance, breast stabilisation and a confined needle trajectory. Our goal is to be able to biopsy a larger percentage of suspicious masses using ultrasound, by clarifying ambiguous structures with mammographic imaging. Using breast phantoms, we have shown that our ultrasound guided biopsy system was capable of targeting artificial lesions that were 3.2 mm in diameter, with a 96% success rate. Through this study, we also demonstrated that our system was equivalent to current clinical practice, for an in vitro biopsy task. Metal beads in known relative positions allowed us to determine the geometry of the SM system, so that stereotactic mammography could be registered to 3D US images. The target registration error was found to be 1.6 mm. This error was dominated by positioning error in the vertical direction (perpendicular to the film surface). As an adjunct to SM, we propose that 3D US could provide more complete imaging information for target identification and real-time monitoring of needle insertion, as well as providing a means for rapid confirmation of biopsy success.

Biopsy, Needle↗
PubMed2002

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.

Animals↗
PubMed2001

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.

Biopsy, Needle↗
PubMed2001

Three-dimensional ultrasound imaging.

Ultrasound is an inexpensive and widely used imaging modality for the diagnosis and staging of a number of diseases. In the past two decades, it has benefited from major advances in technology and has become an indispensable imaging modality, due to its flexibility and non-invasive character. In the last decade, research investigators and commercial companies have further advanced ultrasound imaging with the development of 3D ultrasound. This new imaging approach is rapidly achieving widespread use with numerous applications. The major reason for the increase in the use of 3D ultrasound is related to the limitations of 2D viewing of 3D anatomy, using conventional ultrasound. This occurs because: (a) Conventional ultrasound images are 2D, yet the anatomy is 3D, hence the diagnostician must integrate multiple images in his mind. This practice is inefficient, and may lead to variability and incorrect diagnoses. (b) The 2D ultrasound image represents a thin plane at some arbitrary angle in the body. It is difficult to localize the image plane and reproduce it at a later time for follow-up studies. In this review article we describe how 3D ultrasound imaging overcomes these limitations. Specifically, we describe the developments of a number of 3D ultrasound imaging systems using mechanical, free-hand and 2D array scanning techniques. Reconstruction and viewing methods of the 3D images are described with specific examples. Since 3D ultrasound is used to quantify the volume of organs and pathology, the sources of errors in the reconstruction techniques as well as formulae relating design specification to geometric errors are provided. Finally, methods to measure organ volume from the 3D ultrasound images and sources of errors are described.

Animals↗
PubMed2001

Results of salvage cryoablation of the prostate after radiation: identifying predictors of treatment failure and complications.

PURPOSE: We conduct a critical evaluation of cryoablation of prostate cancer after failure of full dose radiotherapy to identify predictors of treatment failure and complications. MATERIALS AND METHODS: A 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. RESULTS: Of 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. CONCLUSIONS: Salvage 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.

Aged↗
PubMed2000

Prostate boundary segmentation from 2D ultrasound images.

Outlining, or segmenting, the prostate is a very important task in the assignment of appropriate therapy and dose for cancer treatment; however, manual outlining is tedious and time-consuming. In this paper, an algorithm is described for semiautomatic segmentation of the prostate from 2D ultrasound images. The algorithm uses model-based initialization and the efficient discrete dynamic contour. Initialization requires the user to select only four points from which the outline of the prostate is estimated using cubic interpolation functions and shape information. The estimated contour is then deformed automatically to better fit the image. The algorithm can easily segment a wide range of prostate images, and contour editing tools are included to handle more difficult cases. The performance of the algorithm with a single user was compared to manual outlining by a single expert observer. The average distance between semiautomatically and manually outlined boundaries was found to be less than 5 pixels (0.63 mm), and the accuracy and sensitivity to area measurements were both over 90%.

Algorithms↗
PubMed2000

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.

Algorithms↗
PubMed2000

Variability and accuracy of measurements of prostate brachytherapy seed position in vitro using three-dimensional ultrasound: an intra- and inter-observer study.

This paper is a step in investigating whether three-dimensional (3D) ultrasound can be used intraoperatively to replace Computed Tomography (CT) for localization of brachytherapy seeds. In order to quantify the accuracy and variability of seed localization without introducing effects due to tissues, we first report our results with test phantoms. An inter- and intra-observer study was performed to assess the variability of 2 3D ultrasound scan acquisition methods: Tilt 3D scanning and pull-back 3D scanning. Seven observers measured the positions of gold seed markers in an agar phantom twice in each of the three orthogonal image planes. An analysis of variance (ANOVA) was performed to determine the intra- and inter-observer standard errors of measurement (SEM) and the minimum detectable changes in marker position (deltap). Average intra- and inter-observer SEMs for the tilt scan 3D image were 0.36 and 0.40 mm, respectively. Measurements of the pull-back scan 3D image yielded average intra- and inter-observer SEM of 0.46 and 0.49 mm, respectively. A paired difference analysis showed that the lower SEM for the tilt 3D scan image were statistically significant at a significance level of alpha= 0.05. The accuracy of the US measurements was tested by determining marker coordinates from CT images of the phantom in a stereotactic head frame. CT coordinates were matched to the ultrasound (US) coordinates by means of an affine transform. Average matching errors in x, y, and z were 0.02, 0.10, and -0.02 mm, respectively.

Agar↗
PubMed2000

Three-dimensional ultrasound imaging.

Two-dimensional viewing of three-dimensional anatomy by conventional ultrasound limits our ability to quantify and visualize a number of diseases and is partly responsible for the reported variability in diagnosis. Over the past two decades, many investigators have addressed this limitation by developing three-dimensional imaging techniques, including three-dimensional ultrasound imaging. In this paper we describe the development of a number of three-dimensional ultrasound imaging systems that make use of B mode, color Doppler, and power Doppler. In these systems, the conventional ultrasound transducer is scanned mechanically or by a freehand technique. The ultrasound images are digitized and then reconstructed into a three-dimensional volume, which can be viewed and manipulated interactively by the diagnostician with a variety of image-rendering techniques. These developments as well as future trends are discussed with regard to their applications and limitations.

Biomedical Engineering↗
PubMed1999

Sonographic surveillance of abdominal aortic aneurysms: what is the smallest change in measured diameter that reliably reflects aneurysm growth?

OBJECTIVE: The decision to repair an abdominal aortic aneurysm may be based on an apparent increase in aneurysm diameter seen in successive sonographic examinations. However, true aneurysm growth can be diagnosed only if the measured increase in aneurysm diameter exceeds the variability inherent in the measurement. This study uses analysis of variance to determine the smallest change between 2 successive, independent sonographic measurements of aneurysm diameter that reliably indicates aneurysm growth. METHODS: Pairs of independent observers examined 63 patients with abdominal aortic aneurysms. Each observer obtained a sonographic measurement of the anteroposterior aneurysm diameter in the transaxial and longitudinal scan planes, and the transverse aneurysm diameter in the transaxial scan plane. Analysis of variance yielded the total variance associated with each type of measurement as well as the contributions made by variance among aneurysms, variance between observers and residual variance. These components were used to estimate interobserver standard error of measurement, interobserver reliability and the smallest measurement change needed to diagnose true aneurysm growth. RESULTS: Differences among aneurysms made the largest contribution to overall variance. Interobserver reliability was excellent, ranging from 0.89 to 0.94 (with perfect reliability being 1.00). The smallest difference between 2 successive, independent anteroposterior diameter measurements that indicated aneurysm growth at the 95% confidence level was 0.78 cm in the transaxial scan plane and 0.92 cm in the longitudinal scan plane. The smallest difference between 2 successive, independent transverse diameter measurements that indicated aneurysm growth at the same confidence level was 1.05 cm. CONCLUSION: Despite high interobserver reliability, only changes in measured aneurysm diameter greater than or equal to 0.78 cm indicate aneurysm growth at the 95% confidence level. Smaller changes in measured diameter may not be real, but due to variability in measurement.

Aged↗
PubMed1999

Why are residential and school moves associated with poor school performance?

Most research on residential mobility has documented a clear pattern: Residential and school moves are associated with poor academic performance. Explanations for this relationship, however, remain speculative. Some researchers argue that moving affects social relationships that are important to academic achievement. But the association between moving and school performance may be spurious; the negative correlation may be a function of other characteristics of people who move often. We offer several conceptual and analytical refinements to these ideas, allowing us to produce more precise tests than past researchers. Using longitudinal data, we find that differences in achievement between movers and nonmovers are partially a result of declines in social relationships experienced by students who move. Most of the negative effect of moving, however, is due to preexisting differences between the two groups.

Child↗
PubMed1998

Analysis of linear, area and volume distortion in 3D ultrasound imaging.

We have developed a three-dimensional (3D) ultrasound imaging system that uses a side-firing probe, axially rotated under computer control, to acquire a series of 2D images, from which the 3D image is reconstructed. For an undistorted reconstruction, the inner radius R0 of the 2D images and the total scanning angle theta must be known accurately. Here, we describe (a) a theoretical analysis of the relative distortion in image shape, length, area, and volume due to an error delta R in R0 or delta theta in theta; (b) measurements of these in simulated and real 3D images; and (c) a method to calibrate R0, theta, and image scale accurately. Theoretically, all four relative distortions vary as P delta R/R + Q delta theta/theta, where magnitude of P < or = 1, magnitude of Q < or = 1, and R is the average distance of the object from the axis. In every case, the simple theoretical formulas for P and Q agree with image measurements to within the measurement uncertainty.

Algorithms↗
PubMed1998

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.

Analysis of Variance↗
PubMed1998

Similarity in gallstone formation from 900 kcal/day diets containing 16 g vs 30 g of daily fat: evidence that fat restriction is not the main culprit of cholelithiasis during rapid weight reduction.

Diets containing essentially no fat, 1-2 g fat per day, have resulted in cholesterol gallstones. Greater fat may result in less gallbladder stasis. Do gallstones form with greater fat content? We studied 272 moderately obese subjects who had normal gallbladder ultrasonograms. The 900 kcal/day liquid diets contained either 16 g fat (N = 94) or 30 g fat (N = 178) each day for 13 weeks. A second gallbladder ultrasound was performed. Sixteen of 94 (17.0%) of the 16-g fat group developed stones with a weight loss of 18 (+/- 7) kg and a body mass index (BMI) decrease of 6 (+/- 2) kg/m2. Twenty of 178 (11.2%) of the 30-g fat group developed stones (P = 0.18, no difference in stone formation) with similar weight loss of 20 (+/- 7) kg (P = 0.08) and BMI decrease of 7 (+/- 2) kg/m2 (P = 0.04). Substantial fat for rapid weight-reducing diets resulted in gallstone formation. Since experiments have shown that our higher fat diet, containing 10 g fat per meal, results in maximal gallbladder emptying, cholelithiasis from rapid weight loss may not be solely attributable to gallbladder stasis.

Case-Control Studies↗
PubMed1998

Three-dimensional transrectal ultrasound guided cryoablation for localized prostate cancer in nonsurgical candidates: a feasibility study and report of early results.

PURPOSE: A 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. MATERIALS AND METHODS: A 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. RESULTS: In 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. CONCLUSIONS: Although 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.

Cryosurgery↗
PubMed1996

A three-dimensional ultrasound prostate imaging system.

We have developed a three-dimensional (3D) transrectal ultrasound imaging system, based on using a motorized 5 MHz transducer assembly, rotated under microcomputer control, to collect a series of 100 two-dimensional (2D) images, digitized by a video frame-grabber. These are then reconstructed into a 3D image on a computer workstation, permitting the prostate anatomy to be visualized in three dimensions, and distance and volume measurements to be performed. The accuracy of the distance measurements was assessed with a string test phantom, and that of the volume measurements with balloons of known sizes. Also, the resolution degradation engendered by the reconstruction algorithm was assessed by comparing the full-width at half-maximum (FWHM) of string cross-sectional images in the 3D image to their 2D counterparts. The results show that distance and volume measurements are both accurate to about +/- 1%, and that the reconstruction algorithm increases the mean FWHM by 8 +/- 3% axially and 3 +/- 3% laterally.

Endosonography↗