Reflections on Development of Quantitative Computed Tomography

The following article was written by Harry Genant, M.D., Professor Emeritus in the Departments of Radiology and Medicine at UCSF.

Quantitative computed tomography (QCT), which was largely invented at UCSF, has several advantages over dual-energy X-ray absorptiometry (DXA), a medical imaging examination that uses an enhanced form of X-ray technology to measure bone mineral density (BMD). QCT is used to reliably and sensitively measure three-dimensional bone mineral density in the spine or hip, and to separately analyze the compact or cortical bone and the trabecular or cancellous bone.  In a clinical research mode, QCT is often used to help understand how disease affects the skeleton and how innovative therapies impact the density and geometry of the skeleton.  In clinical trials, QCT provides substantially more information than the traditional bone densitometry with DXA.

Unlike DXA, which provides measurements in terms of two-dimensional area density, QCT gives a true three-dimensional volumetric rendering of the bone and allows one to analyze separately the trabecular bone and compact bone, which typically cannot be done with DXA.

During the 1970s, using a CT head scanner, Douglas Boyd, PhD and I did some of the seminal work on QCT.  That work was initially focused on spine BMD measurement.  Back then, UCSF had one of only two or three commercial CT scanners in the nation.  That scanner was developed by EMI, a music company (now famous for recording the early Beatles albums) that was also involved in electronics.

In the 1970s, Dr. Boyd was an adjunct member of the UCSF faculty before later developing the electron beam cardiac CT scanner.  In 1977 we published the first article on the use of dual energy mode for CT-based BMD analysis.

The CT imaging technology progressed rapidly, and as it did, we worked with one of EMI’s first whole body CT systems in the late 1970s and early 1980s to apply this method to the spine, coining the term "QCT." I later published several articles on spinal QCT in the early 1980s with Christopher E. Cann, PhD, who at the time was an Assistant Professor in Residence in Radiology.

At the height of our operation during the 1990s there were about 130 physicians, PhDs and support staff in our Osteoporosis Research Group, or ORG, which evolved into the Osteoporosis and Arthritis Research Group.  The work of the ORG led the way for spinal and ultimately hip QCT bone mineral density measurements.

There were three main sources of funding for that early work.  The National Institute of Health was interested in QCT for osteoporosis diagnosis and monitoring of osteoporosis.  The pharmaceutical industry was conducting clinical trials with new osteoporosis therapies and used QCT to measure the bone response.  The third main funder was NASA, which was seeking our help in measuring bone loss as the result of weightlessness in long-term space flight.  For NASA we worked on developing an in-space QCT device to measure bone loss.  At the time, the Soviet Union was also interested in our medical imaging research, and we went to Moscow to set up the spinal QCT methodology to assess bone loss in cosmonauts before and after space flight.

We originally conceived QCT specifically for bone mineral density assessment of the central skeleton.  Today, QCT is being used in hundreds of medical imaging centers around the world, both clinically and as a powerful research tool using whole body spiral CT scan systems.  The most significant advancement in the past decade has been applying the QCT method for measuring hip BMD, geometry and structure.

The opportunity to help develop QCT while working with some of the great specialists in osteoporosis and musculoskeletal imaging was a highlight of my career. I look forward to future developments in this field from UCSF.