Virtual colonoscopy works by imaging the interior of the colon to look for pre-cancerous polyps, enabling their removal before they can progress into colorectal cancer. Patients undergo an abdominal CT scan that creates cross-sectional images of all structures in the abdomen (including the spine). These images are then processed to create an interior or virtual fly-through view of the colon.
Most physicians recommend that adults undergo regular colorectal cancer screening (via conventional or virtual colonoscopy) from the age of 50. This is also around the age at which osteoporosis - a reduction in bone mineral density that increases the risk of fracture - can start to manifest. This degenerative bone disease affects a large number of people, with more than a third of all female adults likely to fall victim to osteoporotic bone fracture at least once in their lifetime.
By using the same CT data recorded for the virtual colonoscopy and applying different software, the researchers - led by Rizwan Aslam, assistant clinical professor of radiology at the University of California, San Francisco - created 3D images of the patient's spine. These images enabled the measurement of the patient's bone mineral density, potentially allowing early detection (and treatment) of osteoporotic disease.
"Previous researchers have used abdominal CT to obtain information on bone density; we applied it to CT colonography as a novel way to obtain additional information regarding the patient's bone health while they were being screened for polyps," explained Aslam, who presented the study results at this week's annual RSNA meeting in Chicago, IL.
Aslam and team performed a retrospective study comparing bone-mineral-density measurements derived from CT data and with those derived from dual-energy X-ray absorptiometry (DEXA, the standard bone-density screening tool) in the same patients. The group included 30 males and five females, ranging in age from 54 to 79.
A 16-slice MDCT scanner from GE Healthcare was used for the CT scanning, while DEXA was performed using a Hologic Discovery series A machine. The study showed excellent agreement between the DEXA bone-mineral-density scores and the data generated from the virtual colonoscopy, with both tests identifying osteoporotic bones.
"We used a Philips bone-mineral-analysis software package called BMAP," Aslam told medicalphysicsweb. "It essentially uses internal density measurements, using the patient's spinal muscle and fat to obtain a range with which to calculate the bone mineral density. This is instead of using quantitative computed tomography, where a phantom is required."
Aslam noted that CT colonography will not provide a replacement for DEXA testing, but that it could offer a means to screen more people for osteoporosis. "When an individual undergoes CT colonography, we can also obtain a bone-density measurement with no additional radiation and at minimal cost," he explained.
The researchers now plan to perform a prospective study comparing bone-mineral-density values derived with this method with those obtained via quantitative computed tomography (using a reference phantom) in the same patient.