High resolution stationary digital breast tomosynthesis using distributed carbon nanotube x-ray source array

• Published in: Medical physics (Lancaster) Vol. 39; no. 4; pp. 2090 - 2099
• Main Authors: Qian, Xin, Tucker, Andrew, Gidcumb, Emily, Shan, Jing, Yang, Guang, Calderon-Colon, Xiomara, Sultana, Shabana, Lu, Jianping, Zhou, Otto, Spronk, Derrek, Sprenger, Frank, Zhang, Yiheng, Kennedy, Don, Farbizio, Tom, Jing, Zhenxue
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-04-2012
• Subjects: Anodes; BEAMS; biological tissues; BIOMEDICAL RADIOGRAPHY; breast cancer; carbon nanotube x-ray; CARBON NANOTUBES; CATHODE RAY TUBES; Cathodes; Computer-Aided Design; Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps; DETECTION; Devices sensitive to very short wavelength, e.g. x‐rays, gamma‐rays or corpuscular radiation; diagnostic radiography; digital breast tomosynthesis; Digital computing or data processing equipment or methods, specially adapted for specific applications; Digital radiography; Digital tomosynthesis mammography; Equipment Design; Equipment Failure Analysis; field emission; Image data processing or generation, in general; Image Enhancement - instrumentation; Image enhancement or restoration, e.g. from bit‐mapped to bit‐mapped creating a similar image; IMAGE PROCESSING; image reconstruction; image resolution; image restoration; IMAGE SCANNERS; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; INTERFACES; LIFETIME; MAMMARY GLANDS; mammography; Mammography - instrumentation; medical image processing; Medical imaging; Medical X‐ray imaging; Nanotube devices; Nanotubes, Carbon; Nano‐structures; NEOPLASMS; phantoms; Phantoms, Imaging; RADIATION DOSES; Radiation Imaging Physics; RADIOLOGY AND NUCLEAR MEDICINE; READOUT SYSTEMS; Reconstruction; Reproducibility of Results; s-DBT; Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof; Segmentation; Sensitivity and Specificity; SIMULATION; SPATIAL RESOLUTION; STABILITY; Tomography, X-Ray Computed - instrumentation; Transforming x‐rays; Vacuum tubes; X RADIATION; X-RAY SOURCES; X-RAY TUBES; X-Rays; X‐ray detectors; X‐ray optics; X‐ray technique; digital breast tomosynthesis; breast cancer; carbon nanotube x-ray; s-DBT
• DOI: 10.1118/1.3694667
• EISSN: 2473-4209; 0094-2405
• ISSN: 0094-2405

Purpose:
The purpose of this study is to investigate the feasibility of increasing the system spatial resolution and scanning speed of Hologic Selenia Dimensions digital breast tomosynthesis (DBT) scanner by replacing the rotating mammography x-ray tube with a specially designed carbon nanotube (CNT) x-ray source array, which generates all the projection images needed for tomosynthesis reconstruction by electronically activating individual x-ray sources without any mechanical motion. The stationary digital breast tomosynthesis (s-DBT) design aims to (i) increase the system spatial resolution by eliminating image blurring due to x-ray tube motion and (ii) reduce the scanning time. Low spatial resolution and long scanning time are the two main technical limitations of current DBT technology.
Methods:
A CNT x-ray source array was designed and evaluated against a set of targeted system performance parameters. Simulations were performed to determine the maximum anode heat load at the desired focal spot size and to design the electron focusing optics. Field emission current from CNT cathode was measured for an extended period of time to determine the stable life time of CNT cathode for an expected clinical operation scenario. The source array was manufactured, tested, and integrated with a Selenia scanner. An electronic control unit was developed to interface the source array with the detection system and to scan and regulate x-ray beams. The performance of the s-DBT system was evaluated using physical phantoms.
Results:
The spatially distributed CNT x-ray source array comprised 31 individually addressable x-ray sources covering a 30 angular span with 1 pitch and an isotropic focal spot size of 0.6 mm at full width at half-maximum. Stable operation at 28 kV(peak) anode voltage and 38 mA tube current was demonstrated with extended lifetime and good source-to-source consistency. For the standard imaging protocol of 15 views over 14, 100 mAs dose, and 2 × 2 detector binning, the projection resolution along the scanning direction increased from 4.0 cycles/mm [at 10% modulation-transfer-function (MTF)] in DBT to 5.1 cycles/mm in s-DBT at magnification factor of 1.08. The improvement is more pronounced for faster scanning speeds, wider angular coverage, and smaller detector pixel sizes. The scanning speed depends on the detector, the number of views, and the imaging dose. With 240 ms detector readout time, the s-DBT system scanning time is 6.3 s for a 15-view, 100 mAs scan regardless of the angular coverage. The scanning speed can be reduced to less than 4 s when detectors become faster. Initial phantom studies showed good quality reconstructed images.
Conclusions:
A prototype s-DBT scanner has been developed and evaluated by retrofitting the Selenia rotating gantry DBT scanner with a spatially distributed CNT x-ray source array. Preliminary results show that it improves system spatial resolution substantially by eliminating image blur due to x-ray focal spot motion. The scanner speed of s-DBT system is independent of angular coverage and can be increased with faster detector without image degration. The accelerated lifetime measurement demonstrated the long term stability of CNT x-ray source array with typical clinical operation lifetime over 3 years.