Imaging of the Spine: A Medical and Physical Perspective - Spinal Imaging and Image Analysis - page 3

these images include X-ray attenuation properties of tissue, magnetic properties of
tissue, tissue vascular status, and speed of sound propagation.
Imaging modalities may then be divided into categories based on the physical
characteristics used in the visualization. Modalities which are used to visualize
anatomic structures based on tissue densities depend on variation in X-ray atten-
uation properties of tissue within the body to generate anatomic boundaries, and
include radiography and fluoroscopy, as well as computed tomography (CT). The

nuclear magnetic resonance properties of tissue are used in the process of anatomy
visualization by magnetic resonance imaging, which, in effect, forms a map of the
magnetic properties of the tissue of interest. Molecular imaging techniques
encompass a number of imaging technologies, but have in common the assessment
of tissue physiology by tracking of radiolabeled molecules, while additionally
providing rudimentary information regarding body anatomy. Ultrasound uses var-
iation in sound propagation speed through organs and re

fl

fl ection at tissue planes to

create a map of sound propagation characteristics.
Each of the modalities has a different but somewhat complementary part to play
in tissue assessment, evaluating the varying physical properties of tissue. Thus, each
of the different modalities may be thought of as having a speci

c set of optimal

functions for anatomic visualization and solving speci c diagnostic problems. As a

heuristic example, while CT can be optimal for rapid scanning, diagnosis, and
accurate assessment of acute spinal vertebral fracture geometry in trauma patients,
Magnetic Resonance Imaging (MRI) examination is more time consuming,
necessitates co-operation on the part of the patient versus the administration of
anesthesia and monitoring, and may make fine scale evaluation of osseous struc-

tures more dif cult. However, in other circumstances, MRI can be more useful as a

tool for the diagnosis of bone contusions, as well as soft tissue injuries of the spinal
and para-spinal regions. In the case of bone contusion, for instance, MRI inquiry of
the magnetic properties of tissue allows it to highlight reactive bone marrow edema
which is not apparent on CT imaging.
An extensive range of spine pathology can be diagnosed and characterized using
the modalities individually or in various combinations. In the following sections,
modalities currently and commonly used in medical applications are discussed with
illustrative clinical examples.

2 Radiographs

The most common modality of spine imaging based on sheer numbers of studies
performed is the X-ray generated image, the

“ ”

which may be thought of
as a parallel, in some sense, to digital photography. Current generation X-ray
systems produce an X-ray beam via an electronic tube,

radiograph,

filter, and collimator, which
is then projected onto a detector [ 1 ]. Similar to in principle to the optical wave-
length photon detector found in digital cameras, the X-ray detector is also designed