LWBK1006-15 LWW-Govindan-Review December 7, 2011 19:5
176 DeVita, Hellman, and Rosenberg’s CANCER: Principles and Practice of Oncology Reviewfor thoracic imaging because of the air interface with normal lung, sonog-
raphy may be useful for needle guidance in thoracentesis and peripheral
lung lesion biopsy. Occasionally, a mass can be characterized by sonog-
raphy by use of color Doppler. With all of the recent advances, it would
be tempting to discount the role of conventional radiography. One area
in which plain films are still of great value is bone radiography. The high
spatial resolution of bone films allows for lesion characterization that is
complementary to MRI. At Washington University, no bone MRI is inter-
preted without a comparison radiograph. Lack of a comparison bone film
may result in benign disease being confused with malignancy.Answer 15.22. The answer is D.
Nuclear medicine studies are a form of molecular imaging that have been
around for a while but continue to occupy an important role in stag-
ing and diagnosis. This has become even more true in the era of PET
and PET/CT. Nuclear medicine studies rely on the administration of bio-
logically active material (usually injected). Images are then obtained to
document the biodistribution of the material. Although resolution of the
images is somewhat limited, when viewed in conjunction with anatomic
imaging, the studies can be enormously powerful. Because radioactivity is
with the agent that is administered, radiation dose is completely indepen-
dent of the number of images obtained, unlike CT, which increases the
radiation dose with increased number of images. Bone scintigraphy repre-
sents one of the older techniques in which a tracer is injected that is taken
up by osteoblasts. Tumors with a predisposition to osseous metastases are
well imaged by this technique. However, it is very sensitive but not very
specific, because any process resulting in increased bone turnover will
result in increased tracer uptake. As a result, bone scintigraphy should be
reserved for instances in which there is a reasonable likelihood of osseous
metastasis. For example, in prostate cancer, a bone scan is recommended
when serum PSA levels are greater than 10. Another technique that has
been in use for a few years is sentinel node mapping. In this technique,
radiotracer is injected into a tumor and the lymph node drainage pattern
is mapped. The first or sentinel node that is seen can then be biopsied. This
technique is useful when lymph node drainage patterns are unpredictable,
such as melanoma or breast cancer. A recent major advance in nuclear
medicine has been the increased use of PET in the diagnosis and staging
of various tumors. PET relies on the injection of a radiotracer (currently,
usually FDG), which is taken up by metabolically active tissues. These
tissues may represent infection, inflammation, or neoplasm. When com-
bined with CT (PET/CT), this has become a powerful tool in neoplasm
detection and characterization. A major pitfall of anatomic imaging is
that it relies on an abnormal mass or abnormal size of a normal structure
before pathology is appreciated. PET/CT allows for normal-sized struc-
tures (e.g., lymph nodes) with disease to be imaged before they become
enlarged. This has been helpful in accurately staging many different types
of tumors. The advantage of using a simultaneous CT for attenuation cor-
rection is that areas of increased uptake can be more accurately localized.
Another major advantage is that by using spiral CT for the transmission