Multiplet resonances in MRS data from normal and cancerous prostate - Signal Processing in MRS with Biomedical Applications - page 336

Moreover, the results are not entirely consistent that MRSI provides added
value compared to MRI alone, and yet this is what was anticipated, given that
metabolic information should provide greater insight than the morphological
characteristics of the tissue. This, however, was not the case in a multicenter
study whose aim was to localize peripheral zone sextants which contained
prostate cancer among 110 patients prior to undergoing prostatectomy [435].
In that study [435], MRSI reportedly yielded no further diagnostically mean
ingful information compared to MRI alone. As mentioned, after therapy with
transrectal highintensity focused ultrasound, it was only MRI but not MRS,
that provided diagnostically important insights during the followup of pa
tients in conjunction with elevated PSA levels [430]. In yet another study
[436], using the ratio of choline plus creatine to citrate, in 4 healthy volun
teers and 13 patients with prostate cancer, a substantial overlap was found
for various Gleason score levels and there were two false negative cases.
Despite advanced coil design and other technological solutions [419], resolu
tion and SNR remain important challenges to the wider application of in vivo
MRS and MRSI for prostate cancer diagnostics and management. Kundra and
colleagues [402] have cited limitations in the resolution and interpretation of
data from MRSI as important challenges with respect to prostate cancer diag
nosis, staging and surveillance. Attempts to improve resolution and SNR by
increasing the static magnetic field strength are noted to affect the spectral
shape of citrate and its ratio to choline [437]. Kim et al. [437] state that
with the limited existing data using 3T scanners, “it remains debatable as
to whether the potential to improve the diagnostic performance for prostate
cancer staging at 3T will translate to clear benefits” (p. 170).
Another very important drawback of MRSI for diagnostics of prostate can
cer is its reportedly rather low sensitivity in the analysis of smaller lesions
[417]. This could clearly limit the role of MRSI for early prostate cancer
detection, since this is the way that this type of malignancy typically first
presents. Concordant with these observations, Westphalen et al. [429] con
clude that MRbased modalities are still not considered to have any role in
screening for the general population.

11.2 Insights for prostate cancer diagnostics by means

of 2D in vivo MRS and in vitro MRS

Besides total choline at 3.2 ppm and citrate at 2.6 ppm to 2.7 ppm, there are
several other metabolites that may be indicators of prostate cancer. These
have been identified by 2D in vivo MRS and by in vitro MRS.
Using in vivo 2D MRS, Thomas et al. [438] were able to detect multiplets
from spermine which overlap with choline and creatinine on 1D in vivo MRS.