Given the ubiquitous nature of back disorders, magnetic resonance imaging (MRI) of the spine makes up a large part of the caseload at most MRI centers. Several new imaging techniques are particularly useful in the spine and may become a central part of the imaging evaluation of spine pathology. Intrathecal myelography, kinematic MRI, perfusion and diffusion imaging, and "Ultrafast MRI" are techniques that may revolutionize the way we evaluate the spine by not only better depicting known pathologic disorders but likely shedding new light on disorders we currently do not fully understand.
Dr. Anzilotti received his MD from Jefferson Medical
College at Thomas Jefferson University in Philadelphia, PA. He is
currently a fourth-year resident at Yale University, New Haven,
CT, where he will be pursuing a fellowship in
Low back pain is the most common cause of disability in the
United States and an expensive healthcare problem, with an
estimated total cost in 1990 exceeding $24 billion.
In recent years, magnetic resonance imaging (MRI) has become the
imaging modality of choice for the evaluation of the spine.
Not only has this imaging modality nearly replaced computed
tomography (CT) and myelography, but several studies have shown a
continued increase in the utilization of spinal MRI.
As a result, although imaging quality and protocols have been shown
to be highly variable, spinal MRI has become a large part of most
Recently, Rao and colleagues
showed a relative disparity between the growth rates of spinal MRI
and spinal surgeries in the Medicare population. From 1996 through
1998, the growth rate of spinal MRI was 25%, compared to an 11%
growth rate in the number of spinal surgeries performed. One
conclusion that can be drawn from this data is that MRI of the
spine is becoming more sophisticated in its ability to detect and
define spinal pathology and therefore better select patients that
may benefit from surgery.
As spinal MRI has developed and become more sophisticated a
myriad of imaging techniques and sequences have been developed.
Nevertheless, the evolution of this imaging technique is far from
over. Several new techniques are currently being developed, some of
which will no doubt revolutionize MRI's ability to diagnose spinal
pathology. Several of these techniques are reviewed below with
emphasis on the unique diagnostic qualities each one may offer over
standard spinal imaging.
Intrathecal gadolinium enhanced MR myelography
MRI provides excellent depiction of the anatomic structures and
most pathologic abnormalities within the spine. However, several
pathologic states require specific evaluation of the cerebrospinal
fluid (CSF) and its function. For example, evaluation of possible
CSF obstruction or leak, and cystic masses in the intradural and
paradural spaces require evaluation of surrounding CSF
hemodynamics. Traditionally these questions have been addressed
with myelography using iodinated contrast agent and either standard
radiography or CT.
In general gadopentatate dimeglumine (GD) has been shown to be a
safe contrast agent for MRI.
Although adverse reactions to intravenous GD administration have
been described, the majority of these are transient and minor;
typically nausea, vomiting, headache, or dizziness, with an
extremely low reported incidence (0.2% to 0.42%).
While intrathecal injection of GD is not FDA approved, several
animal studies have been reported
and recently Zeng et al
published a pilot study describing this technique in humans. In
addition, Krumina et al
report a series in which 52 patients underwent
intrathecal-GD-enhanced MR myelography without significant adverse
reaction and excellent depiction of spinal pathology. Using a
standard lumbar puncture technique, 0.2 to 1 cc of GD was infused
into the subarachnoid space after being mixed with 3 to 5 cc of CSF
or normal saline. MRI was then performed, including T1-weighted
sequences, resulting in excellent depiction of several pathologic
abnormalities such as spinal stenosis, herniated disks, vascular
malformations, CSF leaks, and paraspinal masses (figure 1). There
were no serious adverse reactions in this series and the incidence
of nausea, vomiting, and headache was similar to standard
The advantage of this procedure is its ability to marry the
excellent anatomic resolution of MRI with the functional evaluation
of the CSF provided by myelography and therefore combine two
commonly utilized imaging procedures into one. While long-term
safety data has not been collected, preliminary data suggests that
this new imaging technique is safe in humans, with an adverse
reaction rate similar to standard myelography.
Since a lumbar puncture is a relatively simple and commonly
performed procedure, the imaging advantages of this technique are
gained with little or no need of added procedure expertise, making
this a technique that could be easily integrated into any radiology
Kinematic spinal MRI
As described by Haughton, "the spine which appears immobile in
our static images, is far from a rigid structure."
Imaging the spine in the supine position completely discounts the
dynamic nature of this structure. Effects of axial loading,
flexion, extension, and rotation cannot be assessed with supine MRI
but have been shown to affect spinal stenosis from disk disease and
By imaging patients in the standing, flexing, and extending
position, degenerative disk abnormalities can be depicted more
Jinkins et al
have developed a .6T magnet that not only allows supine and upright
positioning of the patient but also has an open configuration that
allows flexion, extension, and rotation during MRI.
These techniques and positions allow better delineation of
degenerative disk disease and its effect on the spinal cord and
nerve roots in different positions. Specifically, disk protrusions
and herniations are often more pronounced in the upright and
extended positions (figure 2).
Muhle et al
have already described a classification system of cervical
spondylitic myelopathy based on severity of disease during flexion
and extension. Further work in this field may shed more light
degenerative disk disease and possible reveal a better correlation
between finding and symptoms.
While this imaging technique requires a dedicated magnet for
optimal utilization, further research in this field may make the
use of these systems more prevalent.
Perfusion imaging in the spine
Perfusion weighted MRI (PWI) is an imaging technique that
measures the relative amount of blood volume flowing to a
particular anatomic location. While perfusion measurements can be
obtained with MRI using either an injected contrast agent (GD) or
based on endogenous contrast techniques, the former seems to
provide improved physiologic and tissue contrast.
First proposed by Villringer et al,
contrast-enhanced PWI has been shown to have several applications
in the brain, including evaluation of "tissue at risk" in stroke
patients, differentiating recurrence of hypervascular tumor from
nonneoplastic tissue, staging gliomas based on vascularity, and
evaluation of patients with Alzheimer's disease.
Recently, Hinman and colleagues
showed how PWI could be used to diagnose infectious and neoplastic
processes within the spine. Using a 2D-fast spoiled gradient echo
(FSPGR) PWI, they plotted the slope of enhancement following GD
injection and showed a statistically significant difference between
the slope of increasing signal intensity between normal vertebral
bodies and those with neoplastic or infectious processes (figure
3). This strong correlation of histological diagnosis and PW
imaging characteristics may provide a significant advantage in the
diagnosis of neoplastic or infectious processes in the spine, which
can sometimes be difficult to determine with standard MRI
techniques. Similar findings have been reported by Stabler et al
for the evaluation of myeloma in the spine.
Diffusion imaging in the spine
Diffusion-weighted MRI (DWI) has drastically changed the way in
which ischemia of the brain is evaluated.
Based on the current theory that it can detect differences in the
free or relatively restricted motion of water molecules, this
technique has been shown to be very sensitive to pathologic states
in the brain.
Ischemia, demyelination, and even neoplasm all effect cell
membranes and change the normal diffusion coefficient of neuronal
tissues making them conspicuous on DWI.
In the past, application of DWI to the spine has been limited
because of motion artifact associated with the spine and the
difficulty in obtaining accurate motion corrected images. However,
recently DWI has been used to differentiate malignant versus bland
compression fractures in the spine.
In addition, DWI evaluation of the spine for ischemia should become
more applicable as newer coils and sequences are developed.
Perhaps most exciting is DWIs ability to evaluate the spine for
axonal injury and cord healing.
Because of the innate anisotropic diffusion of the spine in the
craniocaudal direction, cord injury, which disrupts nerve fibers,
is readily detected with DWI. This technique will likely continue
to play an increasingly important role in the evaluation of the
traumatized spine, particularly as treatment for these disorders
Ultrafast MRI of the lumbar spine
As described above, low back pain is a major cause of disability
and health care expenditure in the United States, with MRI being
the gold standard for evaluation of back disorders.
However, in the current healthcare environment, decreasing
reimbursement, coupled with increasing utilization of MRI, have
created a great need to increase efficiency of imaging.
As with MRI in other parts of the body, there is a constant
trade-off between imaging time and quality. In the spine, attempts
to decrease imaging time are particularly difficult, given the
added unique problems of CSF flow and motion artifacts. Sze and
addressed the need to shorten imaging time by showing that fast
spin-echo (FSE) imaging of the spine decreased imaging time while
maintaining accurate depiction of spinal pathology.
Recently, Mastromatteo and colleagues described an "Ultrafast
MRI" technique that drastically decreased scan time.
Using a 1.5T Vision System (Siemens Medical Systems, Iselin, NJ) to
evaluate 79 patients, the researchers reduced the total scan time
for the lumbar spine to 1.38 minutes, compared with 16.53 minutes
for a standard spine MRI series. The entire Ultrafast MRI study
consists of the following three sequences; sagittal HASTE (256
matrix, 1.17 * 1.09 pixel size, 5-mm slice thickness), sagittal 3D
T1 gradient echo isotropic 256 sequence (1.95 * 1.95 1.95 voxel
size), and axial T2 HASTE (1.04 * .98 pixel size with 5-mm slice
Statistical comparison of the Ultrafast imaging sequence to
standard sequences showed an almost perfect diagnostic agreement
while significantly decreasing scan time and reducing costs by a
factor of 11.97 (figure 4).
Although additional studies are needed before this new imaging
technique can be incorporated into mainstream imaging, reducing
scan time and costs, to the degree these authors have reported,
could potentially increase access to MRI for patients with back
disorders, decrease patient anxiety and discomfort, and greatly
increase the efficiency of MRI centers.
Several new imaging techniques specifically tailored to evaluate
the spine have been described. These imaging techniques have the
potential to revolutionize the way we evaluate the spine, by better
depicting known pathologic disorders as well as shedding new light
on disorders we currently do not fully understand.