As the millennium has just passed, it is appropriate to review
the significant advances in spinal imaging that have occurred in
the preceding quarter century. Before then, plain film radiography, conventional
tomography, and myelography with either gas or oily material as
contrast agents had been the only methods available for imaging
abnormalities involving the vertebrae, intervertebral disks, spinal
cord, or cauda equina.
By 1975, a nonionic intrathecal contrast agent, metrizamide,
was approved for clinical use. Unlike oily agents, nonionic contrast
carried negligible risk for arachnoiditis, was absorbable, and thus
eliminated the need for its removal from the thecal sac. Secondly,
its neurotoxicity was minimal, compared with ionic water-soluble
media, which never achieved widespread acceptance in the United
In 1977, the introduction of whole-body computed tomography (CT)
permitted direct cross-sectional imaging of both spinal and paraspinal
structures. However, the margins of the spinal cord could only be
reliably demonstrated after the intrathecal administration of water-soluble
contrast. This procedure is known as CT myelography (CTM). Because
of the greater contrast sensitivity of CT, as compared with plain
film myelographic technique, a smaller, less potentially neurotoxic dose
of contrast agent could be administered for CTM. Nevertheless, this
procedure still requires a lumbar puncture, with its attendant hazards
to the patient.
By 1982, magnetic resonance imaging (MRI) became clinically feasible.
MRI has proven to be superior to CT because the spinal cord and
nerve roots could be visualized directly without the requirement
for intrathecal contrast material. Most significantly, the parenchyma
of the spinal cord could now be imaged and assessed for intrinsic
pathology, such as multiple sclerosis plaques. These lesions may
not alter the shape of the spinal cord, and, therefore, would be
undetectable by CTM. Secondly, MRI provides multiplanar imaging,
including sagittal and coronal orientations, with spatial and contrast
resolution equivalent to the axial plane. Lastly, MRI poses no known
health risk as it uses only radiofrequency energy, not ionizing
radiation as is the case with CT.
Sagittal plane MRI is ideal for extended, rapid evaluation of
the entire vertebral column, a procedure facilitated because the
spine is arranged in a sagittal plane. Recent improvements in MRI receiver
coil design (phased array coil) have provided the capacity to image
the entire spine with excellent detail in less than 10 minutes (Fig.
8-1). This is especially helpful in the evaluation for spinal metastases,
as these patients are often in pain, and thus have difficulty in
remaining motionless for MRI. Newer pulse sequences, including half-Fourier
turbo-spin echo (HASTE), can provide interpretable scans in less
than 10 seconds, albeit with reduced spatial resolution compared
with conventional magnetic resonance studies. HASTE imaging can
also suppress some metal-induced artifacts arising from surgical
hardware (Fig. 8-2), allowing improved visibility of anatomy or
pathology otherwise obscured by these artifacts.
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