With positron emission tomography (PET), doctors can look inside a patient’s body and pinpoint hotspots of malign molecular activity. Secondary tumors, for example, show up as scattered pockets of hyperactive glucose consumption.
Perversely, the specificity that makes PET so revealing impairs its usefulness. Like isolated farmhouses you see at night through an airplane window, PET peaks appear against a dark, featureless background. To reliably associate the peaks with the right organ, doctors need a map of the patient’s body.
Two three-dimensional imaging modalities can provide the requisite map: x-ray computer tomography (CT) and magnetic resonance imaging (MRI). Of the two, CT is easiest to integrate with PET. Because CT and PET both rely on detecting high-energy photons—annihilation photons in the case of PET—their basic technologies are compatible. Nearly all the PET scanners on the market today are PET/CT units.
Combining PET and MRI is more challenging. MRI requires strong magnetic...
