Creation of a CT Image Library for the Lung Screening Study of the National Lung Screening Trial

The CT Image Library (CTIL) of the Lung Screening Study (LSS) network of the National Lung Screening Trial (NLST) consists of up to three annual screens using CT imaging from each of 17,308 participants with a significant history of smoking but no evidence of cancer at trial enrollment (Fall 2002–Spring 2004). Screens performed at numerous medical centers associated with 10 LSS-NLST screening centers are deidentified of protected health information and delivered to the CTIL via DVD, external hard disk, or Internet/Virtual Private Network transmission. The collection will be completed in late 2006. The CTIL is of potential interest to clinical researchers and software developers of nodule detection algorithms. Its attractiveness lies in its very specific, well-defined patient population, scanned via a common CT protocol, and in its collection of evenly spaced serial screens. In this work, we describe the technical details of the CTIL collection process from screening center retrieval through library storage.

Appendices

Appendix A

DICOM Header Changes

The table below identifies the changes made to DICOM headers at the time of deidentification on the laptops at the screening centers and at the time studies are committed to the CT Image Library. Quoted entries are literals.

Not listed here are the so-called “private” or vendor scanner-specific DICOM groups and elements (attributes) that are only retained by laptop deidentification software if used for computing CT pitch. In the Library, all private attributes are removed.

Changes to DICOM Groups and Elements
DICOM Group and Element	Description	Laptop Deidentification	Library Deidentification
0008 0012	Instance Creation Date	“19990102”	“19990102”
0008 0020	Study Date
0008 0021	Series Date
0008 0022	Acquisition Date
0008 0023	Image Date
0008 0013	Instance Creation Time	“1200”	“1200”
0008 0030	Study Time
0008 0031	Series Time
0008 0032	Acquisition Time
0008 0033	Image Time
0008 0050	Accession Number	“ACC”	CTIL Accession Number1
0008 0090	Referring Physician	“REFERRING^PHYSICIAN”	“REFERRING^PHYSICIAN”
0008 1030	Study Description	<blank>	<blank>
0008 1050	Performing Physician	“PERFORMING^PHYSICIAN”	“PERFORMING PHYSICIAN”
0008 1060	Reading Physician	“READING^PHYSICIAN”	“READING^PHYSICIAN”
0008 1080	Admitting Diagnoses	“ADMITTING DIAGNOSES”	“ADMITTING DIAGNOSES”
0010 0010	Patient ID	NLST PID2	CTIL ID3
0010 0020	Patient Name	“PATIENT^NAME”	“PATIENT^NAME”
0010 0030	Patient Birth Date	<blank>	<blank>
0010 0040	Patient Sex	<blank>	<blank>
0010 1040	Patient Address	“ADDR”	“ADDR”
0020 4000	Image Comments	4	4

1. ¹CTIL Accession Number—assigned by CTIL, a six-digit number unique to CTIL ID and participant's NLST screening year.
2. ²NLST PID—assigned by Westat, identifies the screening center and the participant.
3. ³CTIL ID—assigned by Westat, a six-digit number unique to participant.
4. ⁴Includes NLST PID; Screening Year; Visit Number; and flags to indicate which of {Exam Date, Birth Date, Gender} were used to match the study (to be deidentified) against a Westat list containing these values to ensure that, indeed, the selected study is a valid NLST study. This field will be encrypted when the study is “checked-out” of the CT Image Library.

Appendix B

CTIL Inquiries

Specific policies for CTIL use are not yet well defined. Until they are, inquiries should be directed to either:

David Gierda, MD	Guillermo Marquez
Principal Investigator	Early Detection Research Group
LSS-NLST CT Image Library	Division of Cancer Prevention
Mallinckrodt Institute of Radiology	National Cancer Institute
Washington Univ. School of Medicine	Executive Plaza North
510 South Kingshighway	Suite 3066, MSC 7346
St. Louis, MO 63110	6130 Executive Blvd.
	Rockville, MD 20852-7346