Biomedical Engineering Reference
In-Depth Information
Multiple pulses of
HIFU exposure
Line of HIFU
exposure
One pulse of
HIFU exposure
Scanning beam of
HIFU exposure
Line
by
line
Slice by slice
Volume of HIFU
exposure
Slice of HIFU
exposure
FIGURE 15.2
Schematic diagram showing the HIFU conformal therapeutic plan, which is used to ablate the whole volume of solid tumor.
individual patient simultaneously. Therefore, only doctors with
a knowledge base from a specialized training course could per-
form this treatment. The experience that doctors have and rea-
sonable judgment that they can make during HIFU procedures
are important at the early stage of HIFU clinical application. As
therapeutic data are extensively collected for each type of solid
malignancy, improvement is expected in the near future.
angiography (DSA); the latter is single photon emission com-
puted tomography (SPECT), and positron emission tomogra-
phy (PET). Anatomic images can provide accurate anatomical
information about tumor extent, whereas physiologic images
can provide physiologic information on the function of tumors.
They are both acquired as digital data and can be mathemati-
cally processed.
15.6
Medical Imaging in HIFU
ablation
15.6.1 Medical Images Used in HIFU
CT is an x-ray imaging technique used to visualize thin slices of
the body. Early CT scanners employed a translate-rotate motion
and required long times ranging from 20 seconds to 5 minutes
to acquire a complete set of data for one image. Modern scanners
are much faster, acquiring the data for one image in only 1 to 3
seconds. Faster and more accurate CT examination has recently
become possible with a new device, the helical scanner. When
contrast agents are used, enhanced CT can provide improved
visualization of certain tumors. CT images can be used in vari-
ous areas of HIFU treatment, including the delineation of the
targeted volume, the determination of relative geometry of criti-
cal structures, and follow-up evaluation of treatment response.
MRI usually presents unique anatomical information and
tumor detail. It can offer excellent discrimination of certain
tumors with high contrast and good resolution, as well as the
ability to select arbitrary planes such as transversal, sagittal,
and coronal directions for imaging. When contrast agents such
as gadolinium compounds are injected, the appearance of the
resulting enhanced MRI image is much better than that of its
non-enhanced counterpart. The utilization of MRI in HIFU
Recent developments of imaging modalities such as CT and MRI
have dramatically led to significant advances in HIFU therapy.
Accurate anatomical information is an essential precondition
for planning and implementing HIFU procedure to the entire
extent of the malignancy. In fact, radiological and medical
images of various types are employed at each step of the HIFU
treatment process, including diagnosis, assessment of the extent
of disease, treatment planning, treatment and assessment of
tumor response, follow-up, and outcome evaluation. Therefore,
these images are of utmost importance in HIFU treatment.
With the help of new imaging modalities, doctors are now able
to define treatment volumes and critical structures with great
precision, thus reducing marginal misses and energy exposure
to normal tissues. Such capabilities may permit a higher rate of
complete tumor ablation, potentially leading to improvement in
local tumor treatment.
Medical images are classified into two types: ana-
tomic and physiologic images. The former category usually
includes CT, MRI, ultrasonography, and digital subtraction
