Although oncologists regularly
use MRI to fulfil cancer-imaging needs, they tend to supplement it with other methods,
such as spectroscopy. Many such techniques have deepened and broadened MRI application,
but they need further development or investigation via multicenter clinical trials.
With time, the true power of MRI may result from its physiologic and functional
abilities, rather than its simply volumetric depictions, according to A. Gregory
Sorensen of Massachusetts General Hospital in Boston.
In a review of the uses of MRI in oncology,
the author observes that every magnetic resonance imager contains a spectrometer
that can sense spectral variations among tissues, and hardware and software modifications
can allow the device to detect several chemical and imaging signatures of cancer
or chemotherapeutic agents. For example, researchers have used magnetic resonance
spectrometry to detect elevated choline — a correlate of breast cancer —
and to monitor the delivery of chemotherapeutic agents that contain fluorine.
For the brain, doctors have used a
type of MRI called dynamic susceptibility contrast to measure blood volume and flow
rate because these factors tend to increase in tumors.
By detecting the microscopic movement
of water, diffusion MRI can show tissue damage. Doctors can use this technique to
monitor the effects of chemotherapy because diffusion rates change dramatically
as tissue dies. More complex modifications of this technique can show tumor microarchitecture,
which can help doctors plan treatment.
Although physicians have used some
of the aforementioned methods as a primary screen for cancer or to judge cancer
treatment, some newer techniques have not yet entered the clinic. For example, scientists
are examining the ability of MRI to both display differences in blood vessel morphology
— an indicator of malignancy — and to make measurements of tissue elasticity
because tumors are often firmer than surrounding tissue. Because MRI cannot normally
detect its weak signal, work with hyperpolarized carbon is underway. In addition,
researchers are exploring combined MRI-PET scanners. (Journal of Clinical Oncology,
July 10, 2006, pp. 3274-3281.)
MORE FROM PHOTONICS MEDIA