Imaging the Body
by Dorothy Wright
Since Wilhelm Conrad Röntgen’s discovery of x-rays in 1895, radiology has undergone a rapid evolution that has generated increasingly sophisticated imaging technologies, including computerized axial tomography (CT), magnetic resonance (MR), positron emission tomography (PET), ultrasonography (US), combined CT/PET, and dual-energy x-ray absortiometry (DEXA) imaging. Today’s radiologists are applying these technologies to provide unprecedented 2D, 3D and 4D images of human anatomy and physiology, as well as alternatives to more invasive diagnostic and treatment procedures.
Ultrasonography images structures in the body by recording and interpreting the echoes of high-frequency sound pulses reflected by tissues of various densities. US imaging has taken significant strides since the 1980s, when advances in computer technology made it possible to develop 3D-US and 4D-US (i.e., motion 3D-US) imaging, whose volume of data provide very detailed anatomical images. Comparing 2D-US and 3D-US images of a fetal face, for example, is not unlike comparing portraits painted by an impressionist and a realist.
“There are a number of beneficial applications of ultrasonography in ob-gyn, including imaging fetal cleft lip and cleft palate,” says Dolores Pretorius ’74, professor in residence in the ultrasound division of the department of radiology at the University of California, San Diego (UCSD). “It is very difficult to convey to parents what we are seeing with a 2D-US image of the fetal face, but a detailed 3D-US image of a cleft enables them to make a more informed decision about their pregnancy,” she explains. “Parents don’t terminate for the cleft alone, in my opinion; most of them terminate for the risk of associated anomalies in 10-20 percent of babies. There are 250 syndromes associated with clefts, and many of these include mental retardation.”
Pretorius and her husband, physicist Thomas Nelson, are among the leaders in the research, development and advancement of 3D-US and 4D-US. They head the 3D Ultrasound Imaging Group at UCSD, one of the few centers in the country that routinely performs 3D-US and 4D-US under research protocols. In addition to its applications in studies of fetal development, 3D-US is used to image congenital anomalies of the uterus in non-pregnant women, particularly those who are infertile. Outside of ob-gyn, 3D-US and 4D-US are being applied in cardiology and interventional radiology.
“I think 3D-US is the future,” Pretorius says. “I think we will continue to improve the technology and find more clinical applications to benefit physicians and patients.”
To the Bone
Orthopedic surgeons and patients have benefited from the application to the musculoskeletal system of advanced imaging technologies, including computerized axial tomography (CT), magnetic resonance (MR) and ultrasonography. These often replace more invasive procedures such as arthrograms and diagnostic arthroscopic surgeries. CT measures the attenuation of x-rays entering the body from various angles, reconstructing an image of the structure under study in a series of cross sections or planes. MR constructs an image based on measurements of the body’s absorption of radio waves under the influence of a magnetic field.
Technical advances in CT, MR and US over the past several years have greatly increased the diagnostic accuracy of these imaging modalities in diagnosing conditions of the musculoskeletal system, especially in the postoperative patient, where the presence of orthopedic hardware can sometimes be problematic in obtaining diagnostic images, according to Carolyn M. Sofka ‘91, assistant attending radiologist and director of education in the department of radiology and imaging at the Hospital for Special Surgery, New York City.
“Metal — joint replacements, orthopedic plates, nails and screws — can result in significant artifacts when using traditional CT protocols,” Sofka explains. “Knowing the anatomy, the kind of orthopedic hardware present, and the CT physics helps the radiologist adjust protocol parameters to obtain diagnostic images.
“The same is true for MRI,” Sofka continues. “There is a misconception that if there is an orthopedic implant in the extremity or joint of interest, it cannot be imaged with MRI because the artifact is too great. In general, most orthopedic implants can be imaged with MRI, and diagnostic images can be obtained that allow the radiologist to see not only the bones and soft tissues, but also detailed information about the implant itself.”
Sofka says ultrasound is an often neglected imaging modality in the musculoskeletal system; however, it is very good at imaging soft tissues, joint fluid and certain aspects of artificial joints, such as the polyethylene liner in total knee replacements. “We also use ultrasound routinely to guide diagnostic or therapeutic interventions in the musculoskeletal system,” she says.
Anatomy and Physiology
Combined CT/PET scanning, a new imaging technology designed by a physicist at the University of Pittsburgh, is being applied to the diagnosis and follow-up of cancer patients. The CT/PET scanner performs computerized axial tomography (CT) and positron emission tomography (PET) — which images the tissue metabolism of an injected radioactive tracer-labeled compound — in rapid succession. The computer combines these scans, yielding an image of the structure and metabolic activity of the targeted area.
“The benefit of combined CT/PET imaging is that the patient need not be moved from the table, and the imaging is performed in such rapid succession that we need not be concerned about artifacts generated by movement of an organ, such as the bowel,” explains Melanie Brown Fukui ’82, director of the division of neuroradiology at Allegheny General Hospital, Pittsburgh. “It is as close as we can get to simultaneous imaging.”
Combined CT/PET scanning is particularly advantageous for examining patients with cancer of the head and neck, enabling physicians to determine whether a tumor has responded to treatment and, as follow-up continues, whether it has recurred.
“Head and neck anatomy is very complicated and many of the landmarks we use to interpret a CT image can be distorted by surgery or radiation, making it difficult to determine whether a tumor is present,” Fukui says. “The PET image overlays information based on the tissue metabolism of an injected compound such as fluorodeoxyglucose (FDG), a radioactive sugar. A tumor will use more sugar than properly treated tissue, which is no longer metabolically active, and it appears as a hot spot on the image.”
The technology has the potential to guide treatment. “If a patient’s tumor has not responded, or has recurred, another treatment may be required,” Fukui says. “We are better able to determine that with combined CT/PET than with CT or PET alone.
“In the future, it is also hoped that CT/PET will be used by radiation oncologists to direct radiation at the most metabolically active areas of the tumor,” she continues. “This is a promising area of study.”
DEXA Takes Off
Sometimes the use of advanced diagnostic imaging technology goes hand in hand with development of new treatments for a disorder. For example, Food and Drug Administration approval of new drugs to prevent and treat postmenopausal osteoporosis, including bisphosphonates such as Fosamax®, has boosted the use of dual-energy x-ray absortiometry (DEXA) scanning, which measures bone mineral density. The DEXA scanner directs alternating x-rays from two sources at the bone, usually the hip and spine, calculating bone density based on transmission time through the bone.
“DEXA is the gold standard for bone-density scanning,” says Marlene Goodhart Rackson ’78, attending radiologist and director of DEXA scanning at Beth Israel Medical Center, New York City. “It is highly accurate for the detection of osteoporosis, and now that there are good medications available to treat osteoporosis, the use of the technology has really taken off. Five years ago I scanned perhaps five patients a day; now I scan about 25 patients a day.”
Still, Rackson says, many more women who are at risk for osteoporosis would benefit from having baseline and follow-up DEXA scans.
“All postmenopausal women should have a baseline DEXA and a follow-up DEXA in a few years to see if they are losing bone density,” Rackson asserts. “A woman with low bone density has an increased risk of fracture, and the lower her bone density is, the greater the risk.”
Rackson, who is former director of vascular and interventional radiology at Beth Israel, notes that creativity leads to new applications of existing technologies. Within the last five years, embolization — the injection of a substance into a blood vessel to occlude it — has become available to treat uterine fibroids in selected patients, avoiding hysterectomies. These benign tumors cause abnormal bleeding, pelvic pain and pressure.
The patient undergoes an angiogram, in which a catheter is inserted in the femoral artery and snaked through the pelvis under x-ray guidance to the blood vessels supplying the uterus. A polymer material is injected into some of these blood vessels, permanently plugging them. With blood supply reduced, the tumors shrink and symptoms often are alleviated.
“Over the past 30 years interventional radiologists have branched out from the classic indications for embolization, such as gastrointestinal bleeding, to new applications,” Rackson says. “The imaging technology, catheters and materials used for embolization had to mature. Then, frankly, it just needed someone’s creativity to apply it to fibroids.”
Imaging of infants and children poses special challenges. Karen I. Norton ’76, director of the Division of Pediatric Radiology at Mount Sinai Hospital, New York City, performs a wide range of diagnostic and interventional imaging procedures, including x-rays and fluoroscopic exams as well as US, CT and MR.
“The goal of a pediatric radiologist is to provide as much diagnostic information as possible while limiting exposure to radiation, so we rely on ultrasound a great deal,” Norton says.
Mount Sinai also is noted as a center for pediatric liver transplantation, and Norton’s department performs many pre- and post-transplantation imaging studies, including intensive follow-up studies to detect potential complications.
“MR is essential in diagnosing many liver diseases in infants and children,” Norton says. “It has also become the mainstay of detecting some of the complications of liver transplantation because of its ability to image the biliary system without the risks of ionizing radiation and the injection of contrast.”
Recent advances in MR technology have reduced but not eliminated the need for conscious sedation, which has risks.
“Until recently, MR did not have wide application in pediatrics because of the length of time required to perform a scan,” Norton says. “Today’s software enables us to do ultra-fast examinations of children. However, MR still requires us to use conscious sedation in most kids to keep them from moving.”
The department also performs CT imaging using protocols specifically developed to protect children from the long-term risks associated with radiation exposure.
“About a year and half ago, several published studies predicted that even routine CTs within diagnostic range put children at a higher risk for developing cancers of all kinds in adulthood,” Norton recalls. “Many imaging centers were using adult protocols on children. The studies showed the importance of adapting adult protocols for children.
“Everybody realizes that no amount of x-ray is safe, and less is always better,” Norton continues. “CT is a wonderful tool — we just have to use it judiciously.”
About Our Sources
Melanie Brown Fukui ’82 is director of the Division of Neuroradiology at Allegheny General Hospital, Pittsburgh. She also serves as program director of the hospital’s Neuroradiology Fellowship Program and its Diagnostic Radiology Residency Program. A biology major at Bryn Mawr, Fukui earned an M.D. at the University of Pittsburgh School of Medicine. Recent research includes a National Institute of Mental Health-funded study of the neurobiology of treatment for geriatric depression and a study of the efficacy of brain-tumor therapies by quantitative MR.
Karen I. Norton ’76 is director of the Division of Pediatric Radiology at Mount Sinai Hospital, New York City. A music history major at Bryn Mawr, she earned an M.D. at Mount Sinai School of Medicine, where she now is associate professor of radiology and pediatrics. Norton has co-authored numerous presentations and publications in the field of magnetic resonance imaging.
Dolores Pretorius ’74 is professor in residence in the Ultrasound Division of the Department of Radiology at the University of California, San Diego. A physics major at Bryn Mawr, she earned an M.D. at Baylor University. Pretorius has assisted in developing clinical applications for 3D ultrasound with physicist Thomas Nelson at UCSD. Among her many publications, she is co-author of Diagnostic Ultrasound of Fetal Anomalies; Text & Atlas. She also has applied 3D ultrasound in vascular radiology, measurement accuracy and interventional radiology.
Marlene Goodhart Rackson ’78, a muskuloskeletal radiologist, is director of DEXA Scanning and director of the Diagnostic Radiology Program at Beth Israel Medical Center, New York City. She also serves as program director of the medical center’s Diagnostic Radiology Residency Program, and is former director of Vascular and Interventional Radiology. A chemistry major at Bryn Mawr, she earned an M.D. at the Medical College of Pennsylvania. Among her many publications, Rackson is author of chapters on renal disease and percutaneous nephrostomy in the recently published book Vascular and Interventional Radiology: Principles and Practice, and a recent article on DISH, a skeletal disorder, in the Journal of Clinical Densitometry.
Carolyn M. Sofka ’91 is assistant attending radiologist and director of education in the Department of Radiology and Imaging at the Hospital for Special Surgery, New York City. A biology major at Bryn Mawr, she earned an M.D. at the University of Medicine and Dentistry, Robert Wood Johnson Medical School. An assistant professor of radiology at the Weill Medical College of Cornell University, she conducts research on the ultrasound appearance of musculoskeletal conditions, as well as MRI. Among her publications, Sofka is co-author of multiple peer-reviewed as well as invited manuscripts, including “Sonographic Evaluation of Shoulder Arthroplasty” and “MRI of Joint Arthroplasty,” and has co-authored several book chapters, including “Diagnostic Ultrasonography,” in the fourth edition of Diagnosis of Bone and Joint Disorders.
About the Author
Dorothy Wright contributes news and feature articles on science, technology, engineering and general interest topics to a variety of publications, including Civil Engineering, Engineering News Record and Bryn Mawr Now.