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Fig. 13 Sagittal images of the lumbar spine. Sagittal images of the lumbar spine demonstrating
a T2, and b T2 fat saturation imaging. Note mild nonuniformity of fat saturation of the
subcutaneous tissues due to edge effects. High signal
intensity within the spinal canal
is
cerebrospinal
fluid, surrounding the caudal aspect of the spinal cord and nerve roots. Note also
increased signal in the intervertebral discs due to
fl
fl
fluid content of the nucleus pulposus
being imaged, both of which can be associated with localized non-uniform alter-
ations in the applied magnetic
field in the tissue of interest [
10
,
11
]. In cases such as
these, fat saturation is nulli
ed and distorted non-uniformly across the image due to
the change in the local
field environment, with results that can potentially mimic
pathology. An example of this effect in a non-spinal structure (the foot) is shown in
Fig.
14
. There is an alternative methodology to create an effect similar to fat
saturation, termed inversion recovery (IR) imaging. Inversion recovery fat sup-
pression imaging has different physical underpinnings, related to the difference
between the longitudinal magnetization relaxation rates of the protons of water and
fat after an excitation pulse is applied, and less prone to applied
field non-uniform
fat suppression [
8
,
10
,
11
]. An example of IR imaging used in clinical practice is
Short Tau Inversion Recovery (STIR) imaging. In STIR imaging, a speci
cally
timed inversion pulse is applied to suppress the fat signal intensity in the image.
A draw-back of IR imaging is lower relative spatial resolution (Fig.
14
).
As previously noted, PD sequencing is somewhat of a hybrid between the
characteristics of T1 and T2. As a result, PD has higher spatial resolution of the
anatomy being imaged when compared to T2 sequencing, but in general demon-
strates worse spatial resolution than T1. PD sequencing facilitates the detection and
assessment of
ed with the application of fat sup-
pression, due to the increased signal intensity of
fl
fluid in anatomic tissues, ampli
fl
fluid on PD. PD sequencing thus
finds application in spine imaging, combining its relatively high spatial resolution
