LWBK1006-15 LWW-Govindan-Review December 7, 2011 19:5
Chapter 15•Advances in Diagnostics and Intervention 177scan for attenuation correction, the entire process has become faster,
which has resulted in improved patient satisfaction and throughput.Answer 15.23. The answer is D.
A major role of imaging in oncology is to determine the effect of ther-
apy on the clinical behavior of a tumor. To that end, a new study may
show complete response to therapy, partial response (defined as>50%
reduction in the sum of tumor cross products), and stability or progression
(defined as 25% increase in the sum of one or more of the tumor deposits).
In 1994, an attempt was made to create a more reliable method of assess-
ing tumor response. These principles were published as the RECIST guide-
lines. These RECIST principles relied on the same four categories of tumor
response assessment and used unidimensional measurements to quantify
tumor size. RECIST also more strictly defined disease progression. Major
criticism of RECIST rests on the lack of universal application of one mea-
surement to all tumors, which may vary in shape, and the lack of inclusion
of bone or marrow involvement. Newer techniques may make measure-
ment less important in assessing tumor response to therapy. These include
PET, where altered FDG metabolism may be seen as a sign of response,
and rapid perfusion techniques that may measure altered tissue perfusion,
which may be another early sign of tissue response.Answer 15.24. The answer is B.
Neuroimaging continues to be on the forefront of modern anatomic imag-
ing. MRI with contrast has become the standard method for detect-
ing and characterizing intracerebral masses. It is very helpful in diag-
nosing and planning surgery for brain masses, especially those near the
brain stem, posterior fossa, pituitary region, and cerebellopontine angle.
CT is limited in these regions secondary to beam hardening from adja-
cent bone. Although spatial resolution of MRI is higher than CT, intra-
venous contrast is still used. It can be helpful in the detection of small
lesions and meningeal lesions. CT with contrast is usually reserved for
patients unable to undergo MRI or in some cases in which it may help in
refining a differential diagnosis by showing calcium or osseous destruc-
tion. Both techniques are limited in their ability to differentiate between
tumor recurrence and radiation change. Newer techniques have recently
been developed that may allow for improved performance in the MRI
detection and characterization of brain lesions and in the presurgical plan-
ning. These include MR spectroscopy, perfusion, and diffusion-weighted
imaging. Spectroscopy, which relies on noninvasive measurements of
brain tumor metabolites, is useful in guiding biopsy. It is limited, how-
ever, in small lesions (<2 cm) and in those adjacent to bone, fat, or cere-
brospinal fluid.Answer 15.25. The answer is A.
Head and neck cancers can be challenging to detect on imaging. Usually,
CT or MRI is reserved once a lesion is detected by endoscopy. Endoscopy
is far better than imaging for the detection of small mucosal lesions.