A note on CAD
Thank you for publishing the excellent article on mammography computer-aided detection, “CAD: Radiology’s Spell-Checker Looks to the Mainstream” (May 2001, page 44). In addition, your editorial “Taking a Closer Look” (page 7) really hits the nail on the head about the importance of these new products. We very much appreciate the leading role your publication has taken over past few years in bringing awareness to this field. In addition to saving lives, early detection can result in breast conservation treatment, reducing both patient trauma and costs to the healthcare system. You may be interested to know that the American Medical Review TV series with Morley Safer is featuring mammography computer-aided detection on public broadcasting and a Webcast. The Scanis Mammex TR, and our key medical and technical people are the vehicle for this program.

Bob Chapman
Chairman and CEO
Scanis Inc.

Consider QCT
Your article “Trends in Bone Density and Breast Cancer Screening” (May 2001, page 32) issue was timely and informative and I offer the following comment not as criticism, but as a point, which should receive a bit more attention.

The issue is QCT.

Like Image Analysis, Computerized Imaging Reference Systems Inc. (CIRS) has sold QCT standards of reference for over 15 years. QCT is widely used throughout the world. QCT, were all things equal, would probably be the screening modality of choice because only CT can isolate and evaluate the trabecular structure of the central skeleton — that which has the highest rate of metabolic turnover — thus the tissue which reflects demineralization (or response to treatment) the fastest.

However, things are not equal and never will be. So a variety of bone density measurement methodologies are used. All are better than nothing.

Some are very good; some are really great at looking at a specific set of conditions.

You state QCT is less precise than DEXA — that is a true statement.

However, apples and oranges are being measured. The DEXA approach measures total bone (cortical and trabecular). The CT approach measures total trabecular bone only. Total bone has low metabolic turnover.

Trabecular bone has high metabolic turnover.

So, in sum, the choice should not be between DEXA and CT — both are great tools. Rather, both approaches should be widely available and widely used. Clearly, a clinic screening 40 people per day does not need to use a million-dollar machine when a $100,000 machine will do a fine job.

Similarly, a low-volume rural hospital with limited funds should use a multifunction CT scanner rather than a single purpose DEXA scanner.

Specific questions relating to metabolism are best evaluated by Quantitative CT. Like most things in medicine, there is neither one answer nor a simple answer. The community at large is fortunate to have access to both QCT and DEXA.

W.R. Drury
President
Computerized Imaging Reference Systems Inc. (CIRS)

Editor’s note: Readers with interest in bone densitometry should refer to “Boning Up on Densitometry,” on page 62 of this issue.

Correction:
In “Image Archiving: Ready for Prime Time” in the July 2001 issue, the name of Inphact Inc. (Nashville, Tenn.) was misspelled on page 69. We apologize for the error.