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none showed any prostate cancer on biopsy. The cutpoint was chosen by the
criterion: Citrate/(Choline + Creatine) < 1.4. Twenty six of these men
were followed for at least 1.5 years. One patient with a persistently elevated
PSA was diagnosed with prostate cancer over 2 years after the initial MRSI.
Taken together, these findings suggest that prostate biopsy could perhaps be
deferred in patients with an increased serum PSA if MRSI does not show any
malignant voxels [423].

11.1.2 Distinguishing high from low risk prostate cancer

It is pertinent here to quote Cabrera et al. [424] for their statement: “the
lifetime risk of receiving a diagnosis of prostate cancer is 16%, but the lifetime
risk of dying of prostate cancer is ... 3%. The primary dilemma in the
management of this malignancy is distinguishing patients with progressive
disease that will become lifethreatening from patients with indolent disease
that may not require treatment” (p. 445) [424].
It has been noted that clinical nomograms that incorporate MRSI in ad
dition to clinical and histopathological data may improve identification of
patients with low risk prostate cancer who could be candidates for watch
ful waiting. This was defined as “no suspicious volume” apparently based
upon (Choline + Creatine)/Citrate and decreased polyamines. Nevertheless,
the level of certainty is currently considered insu cient to segregate lowrisk
patients from intermediate and highrisk patients, with full confidence [425].
On the other hand, MRSI may help identify aggressive prostate cancer. A
strong linear correlation has been reported between with cancer aggressive
ness, as gauged by the Gleason grade, a decrease in citrate and increased
choline [426, 427].

11.1.3 Surveillance for residual disease or local recurrence

after therapy

The time course and success of hormonedeprivation therapy can be assessed
via MRSI. Metabolic atrophy, namely loss of all metabolic activity on the
MR spectra signifies that this therapy has achieved its intended goal. The
appearance of choline on MRSI in the setting of metabolic atrophy has been
used as an indicator of recurrent or residual prostate cancer [428].
It has also been suggested that MRSI could improve assessment of recur
rence after radiation therapy, which causes fibrotic and atrophic changes that
distort the glandular anatomy. This is manifested in low T 2 weighted signal
intensity on MRI, which is di cult to differentiate from prostate cancer. Here
again, metabolic activity, notably the appearance of choline can be suggestive
of local recurrence and help guide salvage therapy. Preliminary data indicate
that MRSI detected recurrence of prostate cancer accurately after radiation
therapy in over 80% of cases [429].