MR arterial spin labeling proves feasible, safe in children

High-field MR perfusion imaging with arterial spin labeling (ASL) can be performed safely and effectively on clinical pediatric populations for several neurological indications, according to Harvard University researchers.

ASL works by magnetically labeling blood water to allow for quantitative studies of cerebral blood flow. The clinical literature compares ASL's accuracy with that of sophisticated blood perfusion and functional imaging techniques such as dynamic contrast-enhanced MRI, SPECT, and PET. Unlike these, however, ASL does not require the injection of dyes or exposure to radiation. It has not been fully explored in children.

"The technique is safe and fast, and it does not require contrast enhancement," said principal investigator Dr. Ellen P. Grant, chief of pediatric radiology at Massachusetts General Hospital for Children.

Grant and colleagues assessed 32 pediatric patients (ages newborn to 18) scheduled for routine clinical evaluation at 1.5T who underwent whole-brain ASL. Indications included six cases of tuberous sclerosis complex, two traumatic brain injuries, one case of carbon monoxide poisoning, one near-drowning incident, a case of Degos disease, one Rett syndrome, two autistic patients, and several other neurological conditions.

The investigators found that ASL provided additional information not present on routine MRI in at least one-third of cases. They presented findings at the 2005 RSNA meeting.

ASL revealed blood flow patterns ranging from hypo- to hyperperfusion in brain regions that had also been depicted as abnormal on diffusion-weighted imaging. Though somewhat difficult to detect, blood flow differences in similarly appearing tubers in patients with tuberous sclerosis complex were also apparent.

Unlike adults, the brains of most pediatric patients suffering from severe brain oxygen insufficiencies undergo complex reperfusion processes. Conventional wisdom holds that in many of these cases, especially neonates, blood flow becomes too dim for imaging to pick up. ASL contradicts this belief, however, and offers an alternative to more invasive perfusion techniques, especially those posing challenges in the small vascularity of very young patients, Grant said.

"ASL also gets me noninvasive parenchymal blood flow, which is another measure of cerebral function that we don't get with other techniques. Structural imaging doesn't show much on kids having seizures. But perfusion shows a lot more, and ASL takes only about five minutes," she said.

The technique has some shortcomings, Grant told Diagnostic Imaging, but it merits further investigation. Her group's results have been so encouraging that they are only waiting for ASL to become available for online imaging reconstruction to incorporate the technique into their routine protocol.

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