Stationary chest tomosynthesis using a carbon nanotube x-ray source array: a feasibility study.

Chest tomosynthesis is a low-dose, quasi-3D imaging modality that has been demonstrated to improve the detection sensitivity for small lung nodules, compared to 2D chest radiography. The purpose of this study is to investigate the feasibility and system requirements of stationary chest tomosynthesis (s-DCT) using a spatially distributed carbon nanotube (CNT) x-ray source array, where the projection images are collected by electronically activating individual x-ray focal spots in the source array without mechanical motion of the x-ray source, detector, or the patient. A bench-top system was constructed using an existing CNT field emission source array and a flat panel detector. The tube output, beam quality, focal spot size, system in-plane and in-depth resolution were characterized. Tomosynthesis slices of an anthropomorphic chest phantom were reconstructed for image quality assessment. All 75 CNT sources in the source array were shown to operate reliably at 80 kVp and 5 mA tube current. Source-to-source consistency in the tube current and focal spot size was observed. The incident air kerma reading per mAs was measured as 74.47 uGy mAs(-1) at 100 cm. The first half value layer of the beam was 3 mm aluminum. An average focal spot size of 2.5  ×  0.5 mm was measured. The system MTF was measured to be 1.7 cycles mm(-1) along the scanning direction, and 3.4 cycles mm(-1) perpendicular to the scanning direction. As the angular coverage of 11.6°-34°, the full width at half maximum of the artifact spread function improved greatly from 9.5 to 5.2 mm. The reconstructed tomosynthesis slices clearly show airways and pulmonary vascular structures in the anthropomorphic lung phantom. The results show the CNT source array is capable of generating sufficient dose for chest tomosynthesis imaging. The results obtained so far suggest an s-DCT using a distributed CNT x-ray source array is feasible.

Comparison of a stationary digital breast tomosynthesis system to magnified 2D mammography using breast tissue specimens.

RATIONAL AND OBJECTIVES: The objective of this study was to compare the stationary digital breast tomosynthesis (s-DBT) system to a conventional mammography system in a study of breast specimens. Radiologist evaluation of image quality was assessed in a reader study. This study represents the first human tissue imaging with the novel carbon nanotube-based s-DBT device. MATERIALS AND METHODS: Thirty-nine patients, with known breast lesions (Breast Imaging Reporting and Data System 4 or 5) by conventional mammography and scheduled for needle localization biopsy, were recruited under an institutional review board-approved protocol. Specimen images were obtained using a two-dimensional (2D) mammography system with a ×1.8 magnification factor and an s-DBT system without a high magnification factor. A reader study was performed with four breast fellowship-trained radiologists over two separate sessions. Malignancy scores were recorded for both masses and microcalcifications (MCs). Reader preference between the two modalities for MCs, masses, and surgical margins was recorded. RESULTS: The s-DBT system was found to be comparable to magnified 2D mammography for malignancy diagnosis. Readers preferred magnified 2D mammography for MC visualization (P < .05). However, readers trended toward a preference for s-DBT with respect to masses and surgical margin assessment. CONCLUSIONS: Here, we report on the first human data acquired using a stationary digital breast tomosynthesis system. The novel s-DBT system was found to be comparable to magnified 2D mammography imaging for malignancy diagnosis. Given the trend of preference for s-DBT over 2D mammography for both mass visibility and margin assessment, s-DBT could be a viable alternative to magnified 2D mammography for imaging breast specimens.

Dependency of image quality on system configuration parameters in a stationary digital breast tomosynthesis system.

PURPOSE: In principle, a stationary digital breast tomosynthesis (s-DBT) system has better image quality when compared to continuous motion DBT systems due to zero motion blur of the source. The authors have developed a s-DBT system by using a linear carbon nanotube x-ray source array. The purpose of the current study was to quantitatively evaluate the performance of the s-DBT system; and investigate the dependence of imaging quality on the system configuration parameters. METHODS: Physical phantoms were used to assess the image quality of each configuration including inplane resolution as measured by the modulation transfer function (MTF), inplane contrast as measured by the signal difference to noise ratio (SdNR), and depth resolution as measured by the z-axis artifact spread function. Five parameters were varied to create five groups of configurations: (1) total angular span; (2) total number of projection images; (3) distribution of exposure (mAs) across the projection images; (4) entrance dose; (5) detector pixel size. RESULTS: It was found that the z-axis depth resolution increased with the total angular span but was insensitive to the number of projection images, mAs distribution, entrance dose, and detector pixel size. The SdNR was not affected by the angular span or the number of projection images. A decrease in SdNR was observed when the mAs was not evenly distributed across the projection images. As expected, the SdNR increased with entrance dose and when larger pixel sizes were used. For a given detector pixel size, the inplane resolution was found to be insensitive to the total angular span, number of projection images, mAs distribution, and entrance dose. A 25% increase in the MTF was observed when the detector was operating in full resolution mode (70 µm pixel size) compared to 2 × 2 binned mode (140 µm pixel size). CONCLUSIONS: The results suggest that the optimal imaging configuration for a s-DBT system is a large angular span, an intermittent number of projection views, and a uniform mAs distribution over all views. With the detector operating at full resolution, a stationary DBT system can achieve an inplane resolution of 5.1 cycles per mm, which is significantly better than continuous motion DBT systems.