Conclusion and outlooks - Signal Processing in MRS with Biomedical Applications - page 396

Well over a century ago it was physics through the discovery of diagnostic
Xrays, which provided the possibility of noninvasively detecting a number
of tumors. Further innovations through computerized tomography, as well
as positron emission tomography, single photon emission tomography, ultra
sound, together with magnetic resonance modalities were all made possible
through basic research from physics. Each of these is now an indispensable
part of the armamentarium of cancer diagnostics. The greatest promise is
held by molecular imaging which examines pathways of disease through cel
lular and molecular biology in conjunction with diagnostic imaging.
While at its outset molecular imaging was almost synonymous with clinical
Xraybased imaging, it now has a far wider scope, including magnetic reso
nance imaging, MRI, magnetic resonance spectroscopy, MRS, and magnetic
resonance spectroscopic imaging, MRSI. Each of the mentioned molecular
imaging methods is complementary. Especially in the role of screening and
whenever there is a need for heightened surveillance frequency of persons at
increased cancer risk, MRI, MRS and MRSI are advantageous as they are free
from ionizing radiation. Other advantages of MRI and MRSI include sub
millimeter resolution and high contrast among tissues as well as multiplanar
capabilities. In particular, MRI is very sensitive, and being noninvasive and
free from ionizing radiation, has become indispensable for timely cancer de
tection. Its major drawback is poor specificity. On the other hand, MRS en
hances specificity by detecting metabolic features of malignancy. Since molec
ular changes often precede morphological alterations, sensitivity can also be
further improved by MRS. As such, MRSI brings together the rich biochemical
information of MRS with the spatial localization methods of MRI to provide
multiple spectra over a volume of tissue. Therefore, MRSI holds particular
promise for screening and surveillance.
The critical complementary information provided by MRS relative to anato
mical imaging via MRI is metabolic information and, hence, the overall status
of the scanned tissue. Thus far, MRS and MRSI have made great progress in
cancer diagnostics by relying upon at most a handful of metabolites. However,
these methods still are not in the widespread use. Indeed, as a research field
and a clinical diagnostic modality, MRS is considered to be on the verge
of a veritable renaissance. Starting from its status as the wellestablished
nuclear magnetic resonance in physics and analytical chemistry, MRS has
developed to such a point in medicine that it is currently being viewed by
experts as the diagnostic modality which could potentially revolutionize not
only cancer diagnostics, but also guided surgery and target delineation for
radiotherapy. In order to achieve this potential, it is necessary to expand the
often prevailing mindset within cancer diagnostics which has emphasized the
qualitative, morphological characteristics of the tissue under examination.
The first glimpse with a rough metabolic information from MRS and MRSI
is given in the form of spectra via composite, total lineshapes as a function
of frequencies at which various metabolites respond or resonate to the applied
external perturbations.

Such information can be given by the fast Fourier