The Iowa Spine and Brain Institute™, with Covenant Medical Center, provides several types of diagnostic imaging tests to assist in accurately diagnosing a condition.
X-rays are usually obtained first. Then, based on the result of the x-ray, a treatment plan may be developed, or increasingly more sophisticated imaging studies may be completed to more precisely define the source of the pain.
These diagnostic imaging tests may include:
X-rays provide detail of the bone structures in the spine and are used to rule out:
- Instability (such as spondylolisthesis)
They image bones by shooting an x-ray beam through the body. The calcium in bone blocks penetration of the x-ray beam. The image of the bones is then picked up as a shadow on a film positioned on the other side of the patient.
X-rays provide for excellent bony detail because bone consists mainly of calcium. However, discs and nerve roots do not have any calcium, so an x-ray does not capture an image of these structures. An x-ray, therefore, cannot be used to diagnose lumbar disc herniation or other causes of nerve pinching.
X-rays should not be performed in women who may be pregnant.
Computerized Tomography (CT Scan)
A CT scan is essentially a fancy x-ray that can take cross section images of the body. They provide excellent bony detail, yet through multiple views are also capable of imaging for specific conditions, such as:
- Lumbar disc herniation
- Lumbar spinal stenosis
Like an x-ray, a CT scan works by shooting an x-ray beam through the body. Next, a computer is used to reformat the image into cross sections of the spine. This process is repeated at multiple different intervals.
As a result, the spinal canal can be imaged and assessed for specific conditions. With its excellent bony detail, CT scans are very useful for assessing fractures.
Because x-ray beams are utilized, the image does not clearly show nerve roots. CT scans will image large disc herniations but can miss smaller ones.
CT scans should not be performed for women who may be pregnant.
Computerized Tomography (CT Scan) with Myelogram
When combined with a myelogram, a CT scan provides for excellent nerve detail. The myelogram adds some additional risk and expense to the CT scan but provides substantial information about the nerve roots.
A myelogram consists of injecting a radiographically opaque dye (dye that is picked up by x-ray) into the sac around the nerve roots, which in turn lights up the nerve roots.
The CT scan follows and shows how the bone is affecting the nerve roots. This is a very sensitive test for nerve impingement and can pick up even very subtle lesions and/or injuries.
The main risk with CT scans is that they use x-ray beams and should not be performed on pregnant women.
The main risk with a myelogram is the potential for a spinal headache. The spinal headache usually resolves in one to two days with rest and fluids, and seems to be more common for patients with a history of migraine headaches.
Magnetic Resonance Imaging (MRI Scan)
An MRI scan is a completely different technology from an x-ray and CT scan and represents the single most useful imaging study available for spine surgery.
An MRI scan is particularly useful as an aid in the assessment of certain back conditions by providing detail of the spinal disc (such as for degenerative disc disease, isthmic spondylolisthesis) and nerve roots (such as for lumbar disc herniation, lumbar spinal stenosis). MRI scans are also useful to rule out tumors or spinal infections.
An MRI images the spine by using a magnet that goes around the body to excite hydrogen atoms. After the atoms return to their normal level of excitation, they emit energy that is picked up on an MRI scanner. Since humans are composed primarily of water (which is two parts hydrogen), MRI scans provide highly refined detail of the spine's anatomy.
Unlike an x-ray beam, there is no radiation with the magnet so the MRI scans may be done on pregnant women. However, patients with a pacemaker implanted in their heart should not have an MRI scan because the magnetic field will cause the pacemaker to malfunction. Also, anyone who works around metal should first have an x-ray of their eye sockets to ensure that they do no have any metal filings in their eyes, which the magnetic field may cause to migrate and damage the eye during the MRI scan.
An EMG is sometimes recommended to assess the electrical activity of a nerve root. After three weeks of pressure on a nerve root, the muscle the nerve goes to will begin to spontaneously contract. Compression of a nerve will also slow electrical conduction along that nerve. EMG’s are also sometimes useful to distinguish nerve degeneration (neuropathy) from nerve root compression (radiculopathy).
The test involves placing small needles into the muscles, so there is some discomfort for the patient.
SSEP’s are sometimes ordered to assess the speed of electrical conduction across the spinal cord. If the spinal cord is significantly pinched, the electrical signals will travel slower than usual.
Discogram to Diagnose Low Back Pain
A discogram is a test to determine the anatomical source of low back pain for the patient. This procedure is most frequently used to determine if degenerative disc disease is the cause of a patient’s pain. Discograms are also performed to assist in preoperative planning for candidates for a lumbar spinal fusion.
In this procedure, the discographer inserts a needle in the patient’s back into the center of the disc. Radiographic dye is then injected into the disc, and if injecting the dye recreates the patient’s normal pain (concordant), it is then inferred that the specific disc is the source of pain for the patient. If the pain is unlike their normal pain (discordant) it can be inferred that even though the disc may look degenerated on an MRI scan, it is in fact not the source of the patient’s pain. The test itself is painful, but the patient needs to be awake and aware in order to tell the discographer what kind of pain is generated by the injection.
There are a limited number of risks involved with a discogram. Disc space infection is a serious but rare (<0.1%) potential complication. Because the needle passes close to the nerve, there is also slight risk of nerve root damage with the test.
A bone scan is sometimes performed to rule out an inflammatory process (such as a tumor or infection) or an occult fracture (small fracture not seen on an x-ray).
A bone scan is performed by injecting a small amount of radioactive marker into an intravenous line (IV). Three hours later, the patient is placed through a scanner and the radioactive marker will be concentrated in any region where there is high bone turnover.
A bone scan is a highly sensitive test to pick up tumors, infections, or very small fractures because these conditions all result in high bone turnover. It can also be used to determine if a compression fracture of the vertebral body is old or new, as an old fracture will not light up and a new one will.
Bone scans, however, cannot distinguish what a lesion represents, and therefore cannot differentiate between a tumor, an infection or a fracture. Therefore, this type of imaging study usually needs to be followed by a CT scan and/or MRI scan to better characterize the lesion.