Kristy L. Perez

Initial In Vivo Quantification of Tc-99m Sestamibi Uptake as a Function of Tissue Type in Healthy Breasts Using Dedicated Breast SPECT-CT

A pilot study is underway to quantify in vivo the uptake and distribution of Tc-99m Sestamibi in subjects without previous history of breast cancer using a dedicated SPECT-CT breast imaging system. Subjects undergoing diagnostic parathyroid imaging studies were consented and imaged as part of this IRB-approved breast imaging study. For each of the seven subjects, one randomly selected breast was imaged prone-pendant using the dedicated, compact breast SPECT-CT system underneath the shielded patient support. Iteratively reconstructed and attenuation and/or scatter corrected images were coregistered; CT images were segmented into glandular and fatty tissue by three different methods; the average concentration of Sestamibi was determined from the SPECT data using the CT-based segmentation and previously established quantification techniques. Very minor differences between the segmentation methods were observed, and the results indicate an average image-based in vivo Sestamibi concentration of 0.10 ± 0.16 μCi/mL with no preferential uptake by glandular or fatty tissues.

Characterizing the contribution of cardiac and hepatic uptake in dedicated breast SPECT using tilted trajectories

A small field of view, high resolution gamma camera has been integrated into a dedicated breast, single photon emission computed tomography (SPECT) device. The detector can be flexibly positioned relative to the breast and image beyond the chest wall, allowing the system to capture direct views of the heart and liver. The incomplete sampling of these organs creates artifacts in reconstructed images, complicating lesion detection. To understand the limits imposed on a 3D acquisition trajectory, sequential tilted trajectories at increasing polar tilt are utilized to collect data of anthropomorphic phantoms filled with aqueous (99m)Tc in a clinically realistic concentration ratio. The counts collected per projection between different scans and the SNR, contrast and resolution (FWHM) of two hot lesions were compared. As expected, the counts per projection increased when the camera had direct views of the heart and liver, but remained relatively constant at other angles. The SNR, contrast and FWHM were more affected by the insufficient sampling of the data by the large polar angles than by the cardiac and hepatic activity. An upper bound on polar tilt for each azimuthal position reduces the artifacts in the reconstructed images. Such trajectories were implemented to show artifact-free reconstructed images.

Comparison of reduced angle and fully 3D acquisition sequencing and trajectories for dual-modality mammotomography

A dual-modality SPECT-CT system for dedicated 3D breast cancer imaging is under development. Independent dedicated SPECT and CT imaging systems have been integrated onto a single gantry for uncompressed breast imaging. This study examines challenges and tradeoffs involved in integrating the acquisition procedures of two independent imaging systems into a single imaging protocol. The physical limitation of the rotating CT tube beneath the custom patient bed currently provides only a 294 degree scan with the bed low enough for the breast to be in the cone-beam CT field-of-view. The directly coupled SPECT system is therefore also limited if the scans are to be taken simultaneously or in an interleaved fashion. Thus, geometric phantoms are imaged to characterize image degradations due to reduced projection angles for both modalities. Two different acquisitions were performed: one with the central ray of the CT cone-beam aligned with the systems center of rotation and one offset from the center of rotation by 5 cm. Various sized activity- filled lesions in an anthropomorphic breast phantom were imaged, first with uniform aqueous background activity and then with added acrylic pieces to simulate a non-uniform background. Interleaving the SPECT and CT acquisitions into a single scan was also investigated. Iterative reconstruction algorithms are used to reconstruct the data, and the SPECT and CT images are co-registered. Both the cold rod and breast data indicate that removing 75deg of SPECT azimuth al data does not significantly reduce image quality. CT images were also minimally affected if the cone-beam is centrally aligned with the center of rotation, but degraded with the laterally offset cone-beam setup. In the course of these experiments, the patient bed was reconfigured with a larger central hole covered with flexible neoprene, gaining the ability to rotate completely around the breast and dramatically improving CT projection views through the chest wall.

Towards Quantification of Functional Breast Images Using Dedicated SPECT With Non-Traditional Acquisition Trajectories

Quantification of radiotracer uptake in breast lesions can provide valuable information to physicians in deciding patient care or determining treatment efficacy. Physical processes (e.g., scatter, attenuation), detector/collimator characteristics, sampling and acquisition trajectories, and reconstruction artifacts contribute to an incorrect measurement of absolute tracer activity and distribution. For these experiments, a cylinder with three syringes of varying radioactivity concentration, and a fillable 800 mL breast with two lesion phantoms containing aqueous 99mTc pertechnetate were imaged using the SPECT sub-system of the dual-modality SPECT-CT dedicated breast scanner. SPECT images were collected using a compact CZT camera with various 3D acquisitions including vertical axis of rotation, 30° tilted, and complex sinusoidal trajectories. Different energy windows around the photopeak were quantitatively compared, along with appropriate scatter energy windows, to determine the best quantification accuracy after attenuation and dual-window scatter correction. Measured activity concentrations in the reconstructed images for syringes with greater than 10 μCi/mL corresponded to within 10% of the actual dose calibrator measured activity concentration for ±4% and ±8% photopeak energy windows. The same energy windows yielded lesion quantification results within 10% in the breast phantom as well. Results for the more complete complex sinsusoidal trajectory are similar to the simple vertical axis acquisition, and additionally allows both anterior chest wall sampling, no image distortion, and reasonably accurate quantification.

TU‐C‐332‐04: Pilot Patient Studies Using a Dedicated Dual‐Modality SPECT‐CT System for Breast Imaging

Purpose: Acknowledging the limitations/discomfort of mammography has inspired the development of a dedicated SPECT‐CT system to detect breast cancer, monitor therapeutic responses, and improve patient comfort. This system provides semi‐quantitative 3D functional/anatomical imaging of a pendant, uncompressed breast. Fused images can potentially provide more valuable clinical information than independent systems alone. Method and Materials: The SPECT subsystem permits fully‐3D complex acquisition trajectories around the breast, avoiding physical hindrances, overcoming distortions due to inadequate sampling, and allowing lesion detection on the chest wall. The CT subsystem, restricted to circular rotation, uses a quasi‐monochromatic, cone‐beam x‐ray source, which allows for reduced radiationdose and increased contrast between similar soft tissue attenuation coefficients. With no breast compression and an open, common field‐of‐view geometry system, the patient lies prone on a customized patient bed while the hybrid device non‐invasively acquires 3D data underneath. A preliminary investigation on the clinical performance of the hybrid system was done by imaging women with biopsy confirmed breast cancerResults:SPECT patient images can clearly visualize the tracer uptake by the tumor and view into the chest wall. Physical system constraints limit chest wall visualization in the CT patient images and thus patient positioning is under modification. Eliminating overlapping tissues through 3D imaging, the CTimages improve lesion isolation versus 2D imaging modalities. Complementary functional and anatomical image information helps localize suspicious areas for subsequent analysis. Conclusion: Implementation of the worlds first dedicated SPECT‐CT system promises greatly improved visualization of the 3D breast volume. Complementary information from functional and anatomical imaging can guide lesion localization for subsequent analysis. Conflict of Interest: MPT is an inventor of this technology, and is named as an inventor on the patent for this technology applied for by Duke. If this technology becomes commercially successful, he and Duke could benefit financially.

Towards quantification of dedicated breast SPECT using non-traditional acquisition trajectories

Quantification of radiotracer uptake in lesions can provide valuable information to physicians in deciding patient care or determining treatment efficacy. Physical processes (e.g. scatter, attenuation), detector/collimator characteristics, sampling and acquisition trajectories, and reconstruction artifacts contribute to an incorrect absolute measurement of tracer activity and distribution. For these experiments, a cylinder with three syringes of varying radioactivity concentration, and a fillable 800mL breast with two lesion phantoms containing aqueous 99mTc pertechnetate were imaged using the SPECT subsystem of the dual-modality SPECT-CT dedicated breast scanner. SPECT images were collected using a compact CZT camera with various 3D acquisitions including vertical axis of rotation, 30º tilted, and complex sinusoidal trajectories. Quantitative differences in the measured absolute activity values were investigated for each acquisition trajectory to determine the efficacy of an acquisition trajectory to quantify regions of focal uptake. With attenuation and scatter corrections applied, reconstruction image results showed that the measured average activity concentrations in the hot-spot areas corresponded to within 15% of the actual dose calibrator measured activity concentration. More complete sampling trajectories outperform incomplete tilted acquisition trajectories.

Improved chest wall imaging through combined complex trajectories in dedicated dual modality SPECT-CT breast molecular imaging

In the hybrid SPECT-CT breast imaging system currently in development in our lab, patient positioning is a practical compromise between comfort and a need to maximize the imaged volume of breast and chest wall. The integrated imaging system rotates under the patient, with the current CT system restricted to purely azimuthal trajectories at a fixed height, while the flexible SPECT system is capable of fully 3D positioning around the pendant breast. The current patient bed, designed with the aforementioned compromises in mind, separates the top of the CT cone beam from the chest wall, thus limiting the system’s ability to image this important area. This study examines combined complex trajectories, including limited angle tomography for both modalities and raising the entire imaging system during the scan, to more effectively image lesions in or near the chest wall. While emphasizing new CT system trajectories, SPECT trajectories are also investigated to maximize the imaged volume while avoiding contact with the bed or patient. Various sized lesions filled with low and medium concentrations of 99mTc activity (10:1 to 3:1) and CT contrast are imaged using different trajectories. Dual modality projections are post-processed to mimic limited angle trajectories or trajectories that raise the CT system for a portion of the scan. Reconstructed images from data sets with trajectories that removed 60° of SPECT and CT azimuthal data and trajectories combining limited angle acquisition with vertical system shift show a significant increase in observed breast volume while maintaining lesion visibility. Two task-based observer studies are used to further evaluate the visibility of small low-contrast lesions reconstructed with decreasing angular acquisitions and system shifting. Observer study results further indicate that limited angle trajectories and system shifting in mid-scan appear to improve chest wall imaging for this dual modality system.

Initial patient study with dedicated dual-modality SPECT-CT mammotomography

Dual-modality SPECT-CT dedicated breast imaging offers great promise in the detection/staging of cancer and the monitoring of treatment therapies. The sequential acquisition with emission (nuclear) and transmission (x-ray) 3D imaging systems can aid in localizing the radioactive uptake of a tumor from the emission image by using the anatomical structure from the transmission image as a roadmap. Both independent SPECT and CT subsystems are mounted onto a single gantry that rotates around the vertical axis of a pendant, uncompressed breast. To evaluate the feasibility of this dedicated system, geometric phantoms and breast phantoms using fiducial markers were acquired to study the sampling and resolution properties and demonstrate the fusion of the functional-anatomical images. In addition, a preliminary investigation on the clinical performance of the system was done by imaging two women with confirmed breast cancer: one on the independent SPECT system and the other on the SPECT-CT system. Further patient hybrid imaging studies are in progress. This compact dedicated SPECT-CT system is capable of non-invasively providing complementary functional and anatomical fully-3D activity distribution information of the breast, and has the potential to help further enhance the visual and quantitative information over the independent systems.

Analysis of Patient Bed Positioning in SPECT-CT Imaging for Dedicated Mammotomography

Patient positioning on a bed is an integral part of accurate imaging for dedicated 3D breast imaging. For both dedicated breast SPECT (single photon emission computed tomography) and breast CT (computed tomography or computed mammotomography, CmT) which are under development in our lab, maximum access to the breast in the imaging systems field of view is required to obtain the largest imaged breast volume. Accurate bed positioning will be necessary as it may be integrated with a guided biopsy apparatus. Thus, a patient bed with flexible 3D positioning capability is being integrated into the various independent and hybrid 3D imaging systems. The customized bed has both manual and computer controlled positioning capability, and the accuracy and reproducibility of the system are being characterized. Computer controlled positioning and feedback provide seemingly reproducible results. However, gross movements may vary in their accuracy to the given input position. While linear with slopes near 1.0 and intercepts near 0.0cm, lateral (Y) movement translates less than the input amount, while axial (X) movement translates farther than the input amount. Vertical (Z) directional movement follows a quadratic shift with a small dc component with or without added weight on the table. A variety of patient imaging conditions along with x-ray image data are evaluated to demonstrate the reproducibility of positioning accuracy. Individual directional repositioning accuracy is found to be better than multiple, combined directional repositioning accuracy. Imaging results indicate a reproducibility (error) of less than 1mm, which may be suitable for SPECT imaging but perhaps not for higher resolution dedicated breast CT. However, for the independent SPECT system, bed motion is not necessary because the detectors line of sight can already acquire data at the chest wall.

Quantification of tc-99m sestamibi distribution in normal breast tissue using dedicated breast SPECT-CT

The use of Tc-99m-Sestamibi in molecular breast imaging is common due to its preferential uptake in malignant tissue. However, quantification of the baseline uptake in normal, healthy breast tissue is not possible using planar-imaging devices. Using our dedicated breast SPECT-CT system, an IRB approved pilot study is underway to quantify mean activity in normal breast tissue, and to differentiate uptake between adipose and glandular tissues. A cohort of patients at normal breast cancer risk undergoing another diagnostic Sestamibi study was imaged using the breast SPECT-CT system. SPECT images were corrected and quantitatively reconstructed using previously developed methods, and registered with the CT images. The CT images were segmented, and the average activity concentration was measured for glandular, adipose, and total breast tissue. Results indicate no preferential uptake between tissues and low average uptake, which may be used to determine a universal threshold for cancer detection.