Kathleen Surry

Poly(vinyl alcohol) cryogel phantoms for use in ultrasound and MR imaging.

Poly(vinyl alcohol) cryogel, PVA-C, is presented as a tissue-mimicking material, suitable for application in magnetic resonance (MR) imaging and ultrasound imaging. A 10% by weight poly(vinyl alcohol) in water solution was used to form PVA-C, which is solidified through a freeze-thaw process. The number of freeze-thaw cycles affects the properties of the material. The ultrasound and MR imaging characteristics were investigated using cylindrical samples of PVA-C. The speed of sound was found to range from 1520 to 1540 m s(-1), and the attenuation coefficients were in the range of 0.075-0.28 dB (cm MHz)(-1). T1 and T2 relaxation values were found to be 718-1034 ms and 108-175 ms, respectively. We also present applications of this material in an anthropomorphic brain phantom, a multi-volume stenosed vessel phantom and breast biopsy phantoms. Some suggestions are made for how best to handle this material in the phantom design and development process.

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.

3D ultrasound imaging: applications in image-guided therapy and biopsy

Abstract The use of conventional 2D ultrasonography to view 3D anatomy limits our ability to plan and guide interventional procedures. CT and MRI have been used in planning and guiding these procedures due to their ability to provide 3D images with accurate depiction of anatomy. Recent development of 3D ultrasound imaging techniques that are capable of acquiring B-mode, color Doppler and power Doppler images, has allowed the development of image-guided therapy and surgery approaches. Because ultrasound imaging is an inexpensive and compact imaging modality, it is particularly suited for applications in prostate therapy, breast biopsy and monitoring of disease progression in response to therapy.

Comparison of Core Needle Breast Biopsy Techniques

Abstract 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, α, 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.

Temperature dosimetry using MR relaxation characteristics of poly(vinyl alcohol) cryogel (PVA-C)

Hyperthermic therapy is being used for a variety of medical treatments, such as tumor ablation and the enhancement of radiation therapy. Research in this area requires a tool to record the temperature distribution created by a heat source, similar to the dosimetry gels used in radiation therapy to record dose distribution. Poly(vinyl alcohol) cryogel (PVA‐C) is presented as a material capable of recording temperature distributions between 45 and 70°C, with less than a 1°C error. An approximately linear, positive relationship between MR relaxation times and applied temperature is demonstrated, with a maximum of 16.3 ms/°C change in T1 and 10.2 ms/°C in T2 for a typical PVA‐C gel. Applied heat reduces the amount of cross‐linking in PVA‐C, which is responsible for a predictable change in T1 and T2 times. Temperature distributions in PVA‐C volumes may be determined by matching MR relaxation times across the volumes to calibration values produced in samples subjected to known temperatures. Factors such as thermotolerance, perfusion effects, and thermal conductivity of PVA‐C are addressed for potentially extending this method to modeling thermal doses in tissue. Magn Reson Med 46:1006–1013, 2001.

A PVA-C Brain Phantom Derived from a High Quality 3D MR Data Set

A brain mould was constructed by converting the digital surface of a high quality 3D magnetic resonance (MR) data set to a real model, using a stereo lithography apparatus (SLA). The tissue mimicking material (TMM) poly(vinyl alcohol) cryogel (PVA-C) was used to form a homogeneous phantom in the mould. 3D images of this phantom were then acquired in MR, CT and ultrasound. The surface contours of the phantom were compared between each modality and the source image. This phantom is employed in our laboratory as a model of a deformable brain.

Three-dimensional transrectal ultrasound guided high-dose-rate prostate brachytherapy: A comparison of needle segmentation accuracy with two-dimensional image guidance

PURPOSE Conventional transrectal ultrasound guided high-dose-rate prostate brachytherapy (HDR-BT) uses an axially acquired image set for organ segmentation and 2D sagittal images for needle segmentation. Sagittally reconstructed 3D (SR3D) transrectal ultrasound enables both organ and needle segmentation and has the potential to reduce organ-needle alignment uncertainty. This study compares the accuracy of needle tip localization between the conventional 2D sagittally assisted axially reconstructed (SAAR) and SR3D approaches. METHODS AND MATERIALS Twelve patients underwent SAAR-guided HDR-BT, during which SR3D images were acquired for subsequent segmentation and analysis. A total of 183 needles were investigated. Needle end-length measurements were taken, providing a gold standard for insertion depths. Dosimetric impact of insertion depth errors (IDEs) on clinical treatment plans was assessed. RESULTS SR3D guidance provided statistically significantly smaller IDEs than SAAR guidance with a mean ± SD of -0.6 ± 3.2 mm and 2.8 ± 3.2 mm, respectively (p < 0.001). Shadow artifacts were found to obstruct the view of some needle tips in SR3D images either partially (12%) or fully (10%); however, SR3D IDEs had a statistically significantly smaller impact on prostate V100% than SAAR IDEs with mean ± SD decreases of -1.2 ± 1.3% and -6.5 ± 6.7%, respectively (p < 0.05). CONCLUSIONS SR3D-guided HDR-BT eliminates a source of systematic uncertainty from the SAAR-guided approach, providing decreased IDEs for most needles, leading to a significant decrease in dosimetric uncertainty. Although imaging artifacts can limit the accuracy of tip localization in a subset of needles, we identified a method to mitigate these artifacts for clinical implementation.

Stereotactic mammography imaging combined with 3D US imaging for image guided breast biopsy

Stereotactic X-ray mammography (SM) and ultrasound (US) guidance are both commonly used for breast biopsy. While SM provides three-dimensional (3D) targeting information and US provides real-time guidance, both have limitations. SM is a long and uncomfortable procedure and the US guided procedure is inherently two dimensional (2D), requiring a skilled physician for both safety and accuracy. The authors developed a 3D US-guided biopsy system to be integrated with, and to supplement SM imaging. Their goal is to be able to biopsy a larger percentage of suspicious masses using US, by clarifying ambiguous structures with SM imaging. Features from SM and US guided biopsy were combined, including breast stabilization, a confined needle trajectory, and dual modality imaging. The 3D US guided biopsy system uses a 7.5 MHz breast probe and is mounted on an upright SM machine for preprocedural imaging. Intraprocedural targeting and guidance was achieved with real-time 2D and near real-time 3D US imaging. Postbiopsy 3D US imaging allowed for confirmation that the needle was penetrating the target. The authors evaluated 3D US-guided biopsy accuracy of their system using test phantoms. To use mammographic imaging information, they registered the SM and 3D US coordinate systems. The 3D positions of targets identified in the SM images were determined with a target localization error (TLE) of 0.49 mm. The z component (x-ray tube to image) of the TLE dominated with a TLEz of 0.47 mm. The SM system was then registered to 3D US, with a fiducial registration error (FRE) and target registration error (TRE) of 0.82 and 0.92 mm, respectively. Analysis of the FRE and TRE components showed that these errors were dominated by inaccuracies in the z component with a FREz of 0.76 mm and a TREz of 0.85 mm. A stereotactic mammography and 3D US guided breast biopsy system should include breast compression for stability and safety and dual modality imaging for target localization. The system will provide preprocedural x-ray mammography information in the form of SM imaging along with real-time US imaging for needle guidance to a target. 3D US imaging will also be available for targeting, guidance, and biopsy verification immediately postbiopsy.

Three-dimensional image-based planning for cervix brachytherapy with bilateral hip prostheses: a solution using MVCT with helical tomotherapy.

PURPOSE We present a method of three-dimensional image-based planning for cervix high-dose-rate (HDR) brachytherapy for patients with bilateral metal hip prostheses using megavoltage computed tomography (MVCT) imaging. METHODS AND MATERIALS Two patients with bilateral metal hip prostheses were treated with our standard HDR brachytherapy fractionation and critical structure tolerance limits for cervical cancer. MVCT imaging was used for treatment planning because of artifacts present in kilovoltage computed tomography (kVCT), which did not allow visualization of the organs of interest. RESULTS The MVCT images provided adequate contrast to allow the contouring of organs at risk and the digitization of HDR applicators. HDR brachytherapy treatment planning was successfully accomplished based on MVCT images for 2 patients with bilateral metal hip prostheses. CONCLUSIONS Using MVCT imaging eliminated streak artifacts, which improved the image quality for treatment planning. MVCT offers an option for three-dimensional planning for cervix brachytherapy in patients with bilateral hip prostheses.

An early report on outcomes from computed tomographic-based high-dose-rate brachytherapy for locally advanced cervix cancer: A single institution experience

PURPOSE To report our experience using high-dose-rate (HDR) brachytherapy with computed tomographic (CT) imaging for locally advanced cervix cancer, using available resources to optimize the treatment. METHODS AND MATERIALS Fifty-seven women with cervix cancer were treated between September 2004 and March 2008. Patients received external radiotherapy, HDR brachytherapy (7 Gy x4) and concurrent chemotherapy. CT planning was done for each insertion. RESULTS Median age was 53 years (range, 29-89 years); majority (49%) had International Federation of Gynecology and Obstetrics stage IIB. The median follow-up was 22.6 months. There were 4 patients who required laser coagulation for rectal bleeding, and one patient required hemicolectomy for sigmoid stricture. There was no grade 3 or 4 genitourinary toxicity. The Kaplan-Meier overall survival, relapse free, central pelvic and pelvic control at 3 years was 86%, 62%, 89%, and 83%, respectively. Pelvic control for tumors 2 to 5 cm was 95% and 84% for tumors greater than 5 cm. CONCLUSIONS Our early experience confirms that CT-based HDR brachytherapy for cervix cancer achieves disease control comparable to other published series. At the same time, conformal avoidance of organs at risk allows for low rates of toxicity.