Kids can have a hard time sitting still for long imaging exams, particularly when faced with pain or trauma. In the early days of step-and-shoot CT scanners, many young patients required sedation in order to avoid the blurred images and coverage gaps resulting from movement during imaging, greatly increasing the risk and cost of the procedures.
Thankfully, single-detector spiral CT technology arrived in the early 1990s to speed acquisition times, slashing sedation rates by as much as 45%. Now, multidetector-row (MDCT) scanners are revolutionizing pediatric CT once again, according to Dr. Katharine Hopkins, a radiologist at Children's Healthcare of Atlanta in Egleston, GA.
Speaking at Stanford University's recent International Symposium on Multidetector-Row CT in San Francisco, Hopkins said the new technology not only enhances patient safety and comfort, but also brings a wealth of new diagnostic opportunities to pediatric medicine.
"Due to speed alone, replacement of a single-slice scanner with a multidetector-row scanner cut our sedation rate by nearly two-thirds, from 32% to 12%," Hopkins, said.
While sedation of infants has been almost completely eliminated, two-year-olds remain the greatest challenge, and continue to require sedation frequently prior to imaging.
Current multidetector-row scanners acquire four channels of helical data simultaneously. When combined with sub-second gantry rotation, both head and body images can be acquired up to eight times faster than with single-slice scanners, Hopkins said.
Sedation, even when performed with the utmost care, carries serious risks of aspiration, respiratory depression, or even death. While complications can often be avoided, the high costs cannot.
"Sedated patients and their parents spend 2-3 times longer in our department for pre-sedation assessment, intravenous catheter placement, and recovery as compared to non-sedated patients," Hopkins said, noting that for most of that time, the sedated patients receive the dedicated attention of nurses and/or radiologists.
The American Academy of Pediatrics, and more recently the Joint Commission on the Accreditation of Healthcare Organizations, require individualized assessment of each patient prior to sedation, Hopkins said. "They also mandate continuous one-on-one monitoring during sedation until the patient has awakened and met strict discharge criteria."
Faced with these realties, technologies such as MDCT that can reduce the need for sedation are definitely worth pursuing, she said. With MDCT, "personnel and resources previously allotted to performing sedation and monitoring can be directed to greater scanner throughput, and we as radiologists can get back to radiology," Hopkins said.
While the inverse relationship between radiation dose and slice thickness in MDCT is, of course, the same with MDCT as for single-detector scanners, multidetector-row scanners yield slightly higher radiation doses than the lowest single-slice scanners, she said.
Moreover, radiologists tend to use thin collimation routinely with MDCT, Hopkins said, "particularly with children, whose anatomy is small and difficult to resolve." However, thin-slice scanning should be used only when it's likely to be beneficial and relevant to diagnosis, Hopkins said, such as in severe traumatic injuries of the spine.
In order to provide diagnostically adequate images with the minimal radiation dose, radiologists must have a good understanding of how to manipulate scan parameters such as slice thickness, pitch, spiral geometry, and scan duration, Hopkins said. When practical, high-quality multiplanar reformations of CT data can also substitute for multiple imaging procedures.
Several applications of MDCT have benefited patients at Children's Hospital, Hopkins noted, particularly in trauma imaging, where radiographs of young trauma patients, who are often fearful or uncooperative, are difficult to obtain.
In suspected cervical-spine trauma, a study with 1.25-mm spiral slices at 0.8-mm intervals with a table speed of 3.75 or 7.5 mm/second can be performed in seconds, obviating the need for conventional x-rays. However, the c-spine CT of a patient in a neutral position does not supplant lateral flexion and extension radiographs for assessing cervical spine stability, she noted.
Trauma imaging of the thoracolumbar spine is especially well suited to MDCT, she said. While CT should not replace all thoracolumbar spine radiographs, patients who are undergoing CT for other traumatic injuries will benefit from time and dose savings if MDCT replaces redundant conventional radiographs in those patients, Hopkins said.
MDCT imaging of the face and orbits can also improve diagnostic efficiency, with high-quality reformations that closely approximate direct coronal images, she said. These have proved useful in imaging trauma patients with injuries that preclude positioning for coronal CT, and in young children who are unable to sit still for the procedure, she said.
Intravenous contrast requirements are reduced by up to 50% in MDCT imaging, particularly in the neck and chest, because vascular enhancement is needed for a shorter duration. In general, a 5-to-10-second increase in injection delays over single-slice scanners "reduces the risk of outrunning the contrast bolus," she said, although more precise scan timing is needed for studies such as CT angiography and multiphase abdominal CT.
MDCT is especially useful in unstable patients who are not candidates for MRI or sedation, she said.
When applied carefully, MDCT promises diminished sedation, greater patient safety, greater patient comfort, and improved diagnostic efficiency, Hopkins said. And while most new technologies are applied to adults years before they reach pediatric clinical practice, Hopkins said, "MDCT offers far too many advantages to the pediatric patient to ignore at this time."
By Eric Barnes
AuntMinnie.com staff writer
July 7, 2000
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