Pediatric patients that could benefit from an MRI of the abdomen, chest, or pelvis often undergo CT scans instead. Although a CT scan can be sufficient in many cases, an MRI often provides additional information that can influence treatment.
For example, MRIs are particularly suited for revealing abnormalities in soft tissues such as ligaments and cartilage and organs such as the brain and heart. MRIs can provide information about blood flow, be used to detect metabolic changes in tissue, or reveal molecular changes that occur in the early stages of disease well before larger structural changes can be observed.
However, it is difficult to do an MRI on a child because they must hold completely still while lying in a scanner sometimes for over an hour. In addition, the confined space of the MRI machine combined with the loud noises it generates, can upset children making it even more difficult for them to remain still.
Another challenge is that young children have trouble holding their breath on command, a task that is required during a scan of the torso to prevent movements of the chest and abdomen from causing image distortion.
In some cases, doctors can obtain satisfactory MRI images by giving children enough anesthesia to temporarily suspend movement of their lungs and abdomen. The child’s breathing is controlled throughout the scan by a ventilator, but is halted by the anesthesiologist for short intervals when the MRI technician needs the torso to be still.
Shreyas Vasanawala MD. PhD, Associate Professor of Radiology at Stanford University www.radiology.standord.edu reports that this approach can be problematic. “You are taking a procedure that is otherwise non-invasive and turning it into a much bigger deal. Also, there are some risks associated with being under anesthesia along with higher costs for the MRI.”
Vasanawala’s goal has been to design and build special MRI signal receiving coils tailored to a child’s body surrounding the part of the body being imaged to capture the radiofrequency signal produced by the child’s body during an MRI scan.
Vasanawala and his team in collaboration with GE Healthcare constructed parallel arrays of child-size receiver coils for imaging the abdomen. While the reduced size of the coils enhances image clarity, the parallel array layout speeds the scan time by allowing individual coils to pick up the signal from different parts of the body simultaneously rather than sequentially.
To further decrease scanning time, Vasanawala worked with the University California at Berkeley www.berkeley.edu/index.html to implement a technique called compressed sensing. Compressed sensing reduces scan times by gathering only a small fraction of the data conventionally needed to enable reconstruction of a complete magnetic resonance image which is referred to as under sampling.
As a result of the research at Stanford, Vasanawala’s pediatric abdominal MRI program is changing the way children are imaged. “We’ve gone completely to a free breathing approach,” says Vasanawala. “Instead of putting a tube down the throat for anesthesia, the children are lightly sedated. For some children in borderline age groups where in the past they would have had to undergo anesthesia, they are now getting MRIs without anesthesia altogether.”
Vasanawala’s pediatric MRI program enabled a five year old child to avoid a liver transplant, after an initial standard MRI revealed a large tumor on the liver. Doctors at three hospitals unanimously recommended a liver transplant.
At the recommendation of a neighbor, the boy’s parents met with the Chief of Clinical Transplantation at the Stanford University Medical Center who suggested they get another picture of the tumor using Vasanawala’s pediatric MRI technology approach.
The resulting images persuaded doctors that the tumor was operable. During a four hour surgery, the doctors removed the tumor along with 60 percent of the liver. The operation was successful and most of the boy’s liver grew back within six weeks. Today the boy is cancer free and living a normal life.