Our team is pleased to announce the public availability of data from 299 patient CT exams of the head, chest and abdomen, 150 cases from Siemens scanners and 149 cases from GE scanners. All cases have routine dose and simulated low dose projection data, full dose images, and clinical data identifying all pathology. This library is unique in that it includes, for the first time ever, the x-ray projection data used to create cross-sectional images, data that are critical for the development of advanced reconstruction and denoising techniques, including those using artificial intelligence.
The need for open access to patient projection data was recognized by our group and others for a number of years. Our plan to develop these resources became focused at the NIBIB sub mSv CT workshop held on February 24-25, 2011. In 2012, NIBIB announced a sub mSv CT funding program and this work was one aim of our funded proposal.
We are excited to finally make the database publicly available worldwide. It will be rewarding to see what new science comes from having these data available!
The library is hosted by the The Cancer Imaging Archive at https://doi.org/10.7937/9npb-2637.
For each patient CT scan, three types of data are provided: DICOM-CT-PD projection data, DICOM image data, and Excel clinical data reports. DICOM-CT-PD is an extended DICOM format that contains CT projection data and acquisition geometry in a vendor-neutral fashion (1). The de-identified patient projection data were decoded with help of the manufacturer and converted into this open standardized format.
CT projection data are provided for both full and simulated lower dose levels. CT image data reconstructed using the commercial CT system are provided for the full dose projection data. For patients scanned on the SOMATOM Definition Flash CT scanner from Siemens Healthcare, CT image data reconstructed using the commercial CT system are provided for the simulated lower dose projection data. All CT images were reconstructed using a filtered back projection method.
The collection comprises 99 head scans, 100 chest scans, and 100 abdomen scans. Fifty cases for each scan type are from a SOMATOM Definition Flash CT scanner (Siemens Healthcare, Forchheim, Germany). Forty-nine head cases, 50 chest cases, and 50 abdomen cases are from a Lightspeed VCT CT scanner (GE Healthcare, Waukesha, WI).
(1) Chen B, Duan X, Yu Z, Leng S, Yu L, McCollough CH. Technical Note: Development and validation of an open data format for CT projection data. Med Phys. 2015;42(12):6964. (doi: https://doi.org/10.1118/1.4935406)
Acquisition and Noise Insertion
All CT scans were acquired at routine dose levels for the practice at which they were obtained using standard clinical protocols for the anatomical region of interest. Poisson noise was inserted into each projection dataset to create a second projection dataset at a simulated lower dose level. Head and abdomen cases are provided at 25% of the routine dose and chest cases are provided at 10% of the routine dose. The simulation technique accurately models the impact of tube current modulation, the bow-tie filter, and electronic noise (2).
Provided projection data are from right before image reconstruction, i.e., after all preprocessing and taking the logarithm. For reconstruction algorithms requiring statistical information, a noise map, expressed as the noise-equivalent incident number of quanta for each data frame, is provided for data from the Siemens CT system.
Several instructional documents are provided to help users extract needed information from the DICOM-CT-PD files, including a dictionary file for the DICOM-CT-PD format, a DICOM-CT-PD reader, and a user manual.
(2) Yu L, Shiung MM, Jondal D, McCollough CH. Development and validation of a practical lower-dose-simulation tool for optimizing computed tomography scan protocols. J Comput Assist Tomogr. 2012;36(4):477-87. (doi:10.1097/RCT.0b013e318258e891)