Digital Signal Processing Reference
In-Depth Information
In a randomized multicenter study from Japan, this strategy did not lead to
a significant increase in stage I ovarian cancer detection among asymptomatic
women who had passed menopause [325]. There were untoward consequences
of such poor specificity.
In the PLCO Trial study, e.g., falsepositive findings were significantly asso
ciated with lower adherence to the Trial and with emotional distress [326, 327].
In light of the high false positive rates of the existing screening methods, the
U.S. Preventive Services Task Force [328] has recommended against routine
screening for ovarian cancer.
Magnetic resonance based modalities have provided some improvement in
the accuracy with which ovarian cancer is diagnosed. For example, the positive
predictive value of TVUS can be enhanced by combination with MRI, as well
as with Doppler flow imaging or CT. MRI is considered to be the most accurate
of these other morphological imaging techniques for assessing adnexal masses
prior to surgery, as well as for distinguishing benign from cancerous lesions
and in some cases for making a specific diagnosis [329, 330]. In a metaanalysis
comparing the three morphological imaging modalities, MRI was of greatest
incremental value in identifying ovarian cancer when the findings on TVUS
were indeterminate [331]. Nevertheless, with contrastenhanced MRI, which
provided the best results, there were still sixty of 241 (24.9%) false positive
findings from initial TVUS that were not identified as being benign [331].
In contradistinction to CT, it should also be taken into account that MRI
and other MRbased diagnostic techniques entail no exposure to ionizing ra
diation. This could be a particularly relevant consideration for groups at
increased risk of ovarian cancer, for whom there is evidence that exposure to
diagnostic medical radiation may be associated with further elevation in risk
for radiationinduced cancer [332, 333].
Magnetic resonance imaging yields high spatial resolution to examine mor
phology. However, in order to assess more than the anatomic aspects, namely,
to assess biochemistry and tissue physiology of the ovary, functional methods
are needed. As a noninvasive technique providing metabolic information,
MRS enables ovarian tissue characterization at a biochemical level, and there
fore complements MRI for ovarian diagnostics. Via MRS, abnormalities can
also be detected that are not seen MRI, because, as discussed, metabolic
changes frequently precede morphological alterations.
9.1 Studies to date using in vivo proton MRS to evaluate
benign and malignant ovarian lesions
There have been several published investigations using in vivo proton MRS to
assess ovarian lesions [334]-[339]. As of early 2009, there have been in total
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