NLST Images -- General Details
Numbers of Images
LSS: 48,534 CT exams (~12 million images).
ACRIN: xx,xxx CT exams (~ X million images) as of 10/29/2012. ACRIN images are still being loaded and curated; completion expected late November, 2012.
Dates (Study Dates)
The Study Dates are fictitious. While appearing real, they are coded to represent the 3 screening years:
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* In order to calculate 'effective mAs' (=mAs/pitch), one needs to first determine mAs and pitch. Understanding both of these require extensive reading of manufacturer DICOM conformance statements and explanations from the manufacturers. Values neede to determine mAs and pitch are sometimes stored in private attributes. Discussions with manufacturers' engineers allowed us to interpret those private attributes and extract the information necessary to to determine effective mAs, mAs, and pitch. Extractions were made prioir to the removal of DICOM private tags because some contained protected health information (PHI). Where pitch could not be determined, a 'null' is reported.
DICOM Standard -- CT Image Module Attributes: References
The portion of the DICOM Standard describing CT Image Module Attributes may be found in the attachment DICOM-CT-Module-11_03pu.pdf. The 3rd column of the attachment specifies the 'Type' for each attribute; DICOM Data Element Types are described in the attachment DICOM-Data-Element-Types-11_05pu.pdf. Addional details regarding DICOM tags found in the DICOM headers of CT images not found in the DICOM CT Module may be found in the attachments DICOM-General-Equipment-Module-11_03pu.pdf and DICOM-Image-Modules-11_03pu.pdf.