Little is left to chance when imaging children. The psychological and physiological needs of young patients compared with those of adults create unique concerns and require special planning. Reducing the radiation dose, allaying children’s anxiety, and delivering the best scan of each pediatric patient remain crucial priorities. Although pediatric imaging has never looked better, radiologists seek faster MRIs, less radiation from CT scans, and better sedation and distraction methods.
From ultrasound (often the first diagnostic tool for children and a pediatric imaging mainstay) to the more complex MRI (which shows conclusively how a child’s brain is wired) and PET/CT (which reveals metastatic disease and fine tumors), imaging modalities continue to deliver fast, accurate, and rich information?frequently at the center of evaluation, diagnosis, and treatment?so that children can get back to the important business of being kids.
Diego Jaramillo, MD, MPH, chairman of the radiology department at the Children’s Hospital of Philadelphia, says that in terms of pediatric applications, an array of modalities offers excitement, including MRI and functional MRI (fMRI), multi-detector CT (MDCT), PET/CT, magneto-encephalography (MEG), and ultrasound. Also, 3T MRI units continue to develop new imaging opportunities for radiology departments. Better resolution and quicker scan times have added 3T to many hospitals’ lists of necessities.
“We have started using two [3T magnets], and it has proven to be very useful for different types of brain imaging, such as detecting very subtle abnormalities that cause seizures and evaluating subtle tumors and vascular abnormalities,” Jaramillo says. “It also is excellent for the evaluation of vascular abnormalities in the body, for biliary studies, and for small-joint imaging, like the hands and wrists. It’s amazingly good.”
A technologist prepares the patient to go into a 1.5T magnet at The Children’s Hospital of Philadelphia. A faux ceiling and music through headphones contribute to relax the child, improving the patient’s experience and decreasing motion during the study. |
Using fMRI, the Children’s Hospital examines the responses of certain areas of the brain during speech and thought processes, which provides a better understanding of such conditions as dyslexia or autism. Also, fMRI helps identify the healthy brain regions that need to be spared when planning brain surgery.
MDCT seems tailor-made for young, restless patients. What used to take minutes can now be done in 5 seconds, which can mean that fewer children require sedation before being scanned. “With single-slice conventional CT, sedation is required for about half of the children,” Jaramillo explains. “Now, with multi-detector CT, the need for sedation has dropped; in some centers, less than five percent of the children need to be sedated.”
Quicker scans as well as decreased radiation doses have helped reduce the degree of exposure in children. CT scans can change the dose factors as they penetrate different parts of the body. “More recently, the dose can change when imaging front to back, compared with right to left, because you need less radiation to penetrate the body from front to back,” Jaramillo says. In many of the pediatric studies, up to 20% of the radiation dose that would be used in adult studies is used in children, according to Jaramillo.
An area that is a relative newcomer in terms of pediatric applications is PET/CT. The main application in pediatrics has been the study of tumors. “It has gained the most ground [in] the study of lymphoma, but more and more, it has become useful in the study of metastatic disease,” Jaramillo says. “Here at the Children’s Hospital, we have had amazing success in the evaluation of very subtle tumors in the pancreas that were very difficult to evaluate before.”
The Children’s Hospital of Philadelphia takes extra steps to ease pediatric patients. For example, separate cubicles provide privacy and a calm environment for pediatric patients. The area is adjacent to the nursing station, providing easy access and close monitoring of the patients. |
Detecting the magnetic changes in the brain related to the activity of the brain, and with very good temporal resolution, is the role of MEG. “That is something we’re going to start in the next six months and has been used with great success, particularly in evaluation of seizures and to plan surgery for brain tumors,” Jaramillo says. “Going forward, it seems it will be very useful for the study of neurodevelopmental disorders like autism.”
The hope is that using such technologies as fMRI and the complementary MEG will result in earlier diagnoses, as well as an ability to more rapidly assess the response to therapy and to different medications.
More Technological Improvements
In the area of advanced brain imaging, significant improvements in vascular imaging?both in MR angiography and CT angiography (CTA)?have made it possible to obviate the more invasive catheter angiography. This progress is especially important in pediatric imaging.
“We have found, for example, in the context of traumatic neck injury or traumatic skull injury, where there is suspicion of a vessel injury, that we can use CTA,” says Gary Hedlund, DO, president of the American Society of Pediatric Neuroradiology (ASPNR of Oak Brook, Ill) and director of MR imaging at Primary Children’s Medical Center (Salt Lake City). “This very rapid technique [helps us] to gain very detailed information about the neck, skull base, and internal vessels of the brain.”
Likewise, in preparation for certain surgeries, either venous or arterial techniques in surgical planning can be performed with CT or MR. Again, this planning eliminates the need to use a catheter angiogram study, which has more morbidity?particularly in a very young child, whose vessels (the femoral arteries, for example) are much smaller than in adults. Hedlund says these techniques have been very useful.
Unlocking some of the functional facets of the brain falls upon fMRI. The technology’s capability shows promise to provide functional information about the brain that relates to language (receptive or expressive), motor tasks, activities, and learning. “These are all very exciting areas that are being worked with, and they’re finding some clinical applications in both pediatric and adult patients,” Hedlund says.
Through diffusion tensor imaging (which measures the movement of water in the brain, detecting areas where the normal flow of water is disrupted to indicate where there could be an underlying abnormality), experts can look at the white-matter tracks?the “highways” of nerves in the brain?and the volume, development, and positioning of some of these tracks that could be distorted by such things as tumors. “We’d like to know where a given eloquent motor track is,” Hedlund says. “We identify that with diffusion tensor imaging, and it’s an exciting area to look at when investigating such conditions as developmental delay.”
Metabolic Inroads
Currently at St Jude Children’s Research Hospital (Memphis, Tenn), Beth McCarville, MD, assistant member in the department of radiological sciences, is working on a protocol to use the T2* (pronounced T2 star) technique on MRI to evaluate the amount of iron in the liver and heart of children who require chronic transfusion for sickle cell anemia. To obtain a T2* measurement, multiple axial images are obtained in one specific area of the organ of interest (heart or liver). The images are obtained using different echo times. The T2* value is then determined by analyzing the same region of interest (ROI) on each of the images and obtaining the mean signal intensity within that ROI for each of the different echo times (each image). These mean signal intensities then are plotted against their respective echo times, and the T2* value is derived from the curve of the plot using a mathematical model.
“These patients who are on chronic transfusion accumulate the iron they receive in the blood product in their body, most importantly in the heart and the liver, and it’s hard to control that and to measure the amount of iron present in those organs,” McCarville says. “The only way they can do that now is with a liver biopsy, which is an invasive procedure. We’re hoping that by using this T2* technique, it can noninvasively measure the amount of iron in the liver and the heart.”
The hospital expects the protocol to be ready this month. The study, which will be completed in about 1 year, will include roughly 50 patients in the 7- to 18-year-old range.
In oncology, a focus at St Jude, ways of measuring the metabolic activity of tumors remains a pressing need, because some of the treatments currently being used do not always result in a change in the tumor’s size.
“They don’t always shrink the tumor, although there could be a reduction in the metabolic activity of the tumor,” McCarville says. In Hodgkin’s disease, for example, the patient often will have a persisting mass on a CT scan, but it might not be metabolically active. Fluorodeoxyglucose-PET (FDG-PET) obtains the information about the metabolic activity of Hodgkin’s lymphoma, but more techniques are needed.
“I think we need other methods of assessing other types of tumors that will give us more information about the metabolic activity of tumors and will give us some idea of how they’re really responding to chemotherapy,” she says. “Molecular imaging is really the wave of the future?being able to measure the activity of tumors.”
And according to McCarville, a lot of research is being performed in that area. She is working on a study using contrast-enhanced ultrasound, measuring and quantitating contrast-agent flow into tumors that are treated with a variety of anti-angiogenic agents. “I’m using that as a surrogate marker of blood flow, because we expect the tumors that are treated with the anti-angiogenic agents to have diminished blood flow,” she explains. “We’ve found that measuring and quantitating the amount of contrast-agent flow on ultrasound [is] an accurate measurement of the blood flow in tumors.”
The importance of earlier or better detection of disease with PET or PET/CT can change the management of the patient. If radiologists find that PET and PET/CT are better for detecting sites of metastatic disease at diagnosis that might be missed by other modalities?such as bone scan, CT, or MRI?then they can better tailor the chemotherapy used to treat the patient.
The general hope is that using T2* mapping might enable earlier detection of abnormalities to the cartilage. This procedure would be useful for children with osteochondrial lesions of the joints, which commonly occur more often in the knees in children, as well as for children with ligament tears and injuries to the cartilage in joints.
Sports and Spines
Along with her colleagues at the Hospital for Special Surgery (HSS of New York), Sherri Birchansky, MD, chief of neuroimaging and associate attending in the department of radiology and imaging, is seeing more sports injuries occurring at younger ages.
“We use MRI for a lot of things in kids, [including] tumors and sports injuries,” Birchansky says. “Kids are now going into Little League and gymnastics, and working out a lot harder and longer, so we’re seeing [many] more sports and overuse injuries. I think that MRI has become more widely used evaluating children with knee pain and shoulder pain. We’re seeing injuries in children that, in the past on MRI, we didn’t see until they were late teens or college age.”
At HHS, MRI also is being used to look at developmental disorders, including scoliosis, to evaluate the cause of the condition and to be sure that there is no underlying anomaly of the spine prior to surgery. In addition, MRI is being used to study physeal maturity and physeal bars in patients who have had injuries to the growth plates?plates of cartilage between the epiphysis and metaphysis?where the longitudinal growth of bone takes place.
With scoliosis patients, the indication for imaging the spine is generally as a preoperative workup to help determine the condition’s cause and to make sure that it has no underlying ideology. “It’s a very nice test to do because you not only see the bone, which X-rays show, but you also can see the spinal cord [and] whether there are underlying tumors in the spinal cord or something that might require neurosurgical intervention, as opposed to just orthopedic intervention,” Birchansky explains. “There is no age limit for performing MRIs on scoliosis patients; it is done even in select newborns. MRI is the ideal modality used in distinguishing isolated vertebral anomalies from abnormalities that also include the neural elements?a very important distinction in the workup, treatment planning, and prognosis of these children.”
A Calming Effect
No matter how sophisticated and finely tuned imaging technologies become, one characteristic that they all share is their potential to frighten children. One of the most important elements of a pediatric radiology department is its ability to make children feel comfortable and to help them understand what is happening. Heidi Miner, certified child life specialist of Primary Children’s Medical Center (Salt Lake City), says that every child is different and requires his or her own special preparation, based on individual fears and experiences.
“For kids, one of the biggest fears they have is not knowing what’s going to happen, especially the younger kids,” Miner explains. “Preparation is one of the most vital things you can do in a hospital for a child. Many times for an MRI, children are worried that they’re not coming out of the machine?that the machine will close up, and they’ll get stuck. With CT scans, because the machine is so big, they don’t know if it’s going to come down and smash them [as one little girl said] ?like a cookie.’ ”
At Miner’s facility, the children are told exactly what will happen as well as what they will see, hear, and feel. The approach has been a great success. Good human interaction, no matter what the patient’s age, pays dividends.
Lin Muschlitz is a contributing writer for Medical Imaging.