Spinal Imaging

Introduction

The established view of the pre-eminence of MRI in spinal imaging is now being challenged by the growing appreciation of the value of MDCT. This is obvious in the assessment of spinal trauma but experience is showing its value in many acute and subacute spinal presentations. Because MDCT can examine large spinal volumes rapidly, it is of great value in the assessment of possible spinal cord compression. Experience has shown that benign, malignant, and infective compression can be shown well with MDCT. This is important because many patients with spinal compression have their imaging delayed waiting for MR, and then up to 20% are excluded on safety grounds or find MR impossible to tolerate because of pain and the need to lie supine for a long time. MDCT can examine patients in any position they find acceptable in a matter of seconds. Accurate surgical localization is possible and the bone detail provides definitive information on spinal stability.

Degenerative disease of the cervical spine is simplest if examined with MR but MDCT will show soft disc and osteophytes well and any associated root compression. Primary or relapsed postoperative lumbar disc disease is also well shown in a CT examination tolerated despite severe pain or obesity. MDCT is often very useful in the acute situation when pain and lumbar spasm necessitates a quick accurate examination.

The entire lumbar spine can be imaged to exclude or confirm a clinical diagnosis of spinal claudication, giving excellent bone, disc, and ligamentous definition where MPR can straighten out any rotational scoliosis common in the elderly degenerate spine. The standard three planes of MR greatly limit this full assessment. Mass lesions at the craniocervical junction are optimally examined with MDCT as has been illustrated in Chapter 12.

In acute trauma, multiple noncontiguous fractures are common so it is essential to include all suspected levels of injury, or a complete spinal region, with a thin section helix to provide a complete assessment. MDCTA is easily incorporated with the bone assessment if vessel injury is likely or suspected (see Chapter 8). Low-dose techniques can be effective in the cervical region.

For suspected spinal compression the basic technique is for very thin slice acquisition following rapidly after 100 ml of IV contrast given by hand or at 2 ml/sec. This increases the definition of the spinal cord, enhances the venous plexus to contrast with disc prolapse or osteophyte compression, and enhances infective/inflammatory/tumour tissue, differentiating it from the neural structures.

Spinal dural fistula and other vascular lesions can be accurately defined by MDCTA which is now able to replace diagnostic spinal angiography if surgical treatment is planned for a fistula, or guide and shorten a diagnostic or therapeutic spinal catheter angiogram.

For ease of understanding, the variety of different CT techniques applied to the spine, which are determined by the clinical site and possible pathology present, will be considered first. The pathologically based illustrations will follow to include all spinal areas.

Technique

CT for lumbar disc disease

Table 13.1 presents optimal patient preparation, and the protocol is presented in Table 13.2. A surview is shown in 13.1.

Multiplanar reformations

The dataset is used to create 8 axial multiplanar reformats parallel to each disc space using a slice width of 2.5 mm and a slice interspace of 2.5 mm; if the patient is very large a thicker slice (3-5 mm) will improve image quality.

Cervical/thoracic disc

For cervical or thoracic disc assessment the technique for spinal cord compression (see later) is best, but limited to the area of clinical interest. The contrast given enhances the epidural veins to aid the identification of small lesions.

Table 13.1 Patient preparation for CT lumbar spine in disc disease

The patient should be positioned supine with knees flexed in order to minimize lumbosacral curve
If the patient has had surgery to the affected area more than 6 weeks or less than 10 years ago an injection of contrast media is required to distinguish between residual disc and fibrous tissue
100 ml of contrast should be injected either by hand or pump (2 ml/sec). No special timing is needed – the patient is scanned when the injection is finished

Spinal stenosis

When clinical history is suggestive of spinal stenosis (neurogenic claudication), the same parameters can be used to scan a larger area from the top border of L1 to the lower border of S1 (13.2). A series of MPRs parallel to the discs is made, with one axial slice at the level of the pedicles and one through the disc of each level from L1 to S1 as illustrated (13.2A, B). Additional reconstructions can be made if an additional disc prolapse or other bone pathology is found.

Table 13.2 Protocol for CT lumbar disc disease

Patient position	Supine
Surview	Lateral
First slice	Mid body of L3 (upper border of L1 for stenosis)
Last slice	Lower border of S1
Field of view	˜250 mm
Slice width	1 mm
Slice increment	0.5 mm
Pitch	0.875
Collimation	64 × 0.625 mm
Rotation time	1.5 sec
kV/mAs	120 kV/300 mAs
Resolution	Standard
Filter	Soft tissue
Reconstructive zoom	As appropriate to include vertebral body
Windowing	WC 60
	WW 360
Contrast	See Table 13.1

13.1 Surview and cover for lumbar disc disease (A). (B, C) Axial MPRs through disc spaces L3/L4 and L5/S1 from the base data. This is done for each of the three lower disc spaces examined. Sagittal plane MPRs (c. 12 images) are also done – slice width 3 mm and interspace 3 mm.

13.2 (A) Surview and coverage for spinal stenosis. (B-D) The angled 2.5 mm MPR axial reformats as described for L1 and L2. All levels are appropriately angled. Slice width 2.5 mm and interspace 17-20 mm depending on size of vertebrae.

Extended spinal area examinations

Table 13.3 presents optimal patient preparation and Table 13.4 presents the parameters for CT spine. The parameters and techniques for CT scanning of the spinal column are broadly similar, the only differences being in the use of suitable filters, contrast administration, and timing.

AP and lateral surviews for planning a thoracolumbar study are shown in 13.3. It should be extended if the cervical spine is to be included and/or reduced if only upper motor neurone features are present. If possible, dual projections are useful for spinal planning to ensure correct levels. For complete thoracic cover start the scan at C6.

In many situations the whole spine should be examined from the foramen magnum to the coccyx. If there is any doubt about the level of the possible pathology it is better for the scan to be inclusive and not exclusive.

CT for spinal trauma

The minimum cover is one vertebral level above to one level below the fractured vertebrae; however, multiple level fractures are common and the extent of injury not always clear on in initial clinical assessment and, increasingly, with the efficiency of MDCT, complete spinal areas are examined.

Resolution: high

mAs: 150

Filter: bone

Table 13.3 Patient preparation for spinal CT

For any patient experiencing pain it may be worthwhile to get the ward staff to administer strong pain relief before the examination to enable the patient to cooperate throughout the scan
For CT myelography the patient should be prepared and consented for lumbar/cervical puncture

CT for cord compression

Plan the scan appropriate to the clinical findings and put the scanner to the start position. Give IV contrast: 100 ml by rapid hand injection, or 100 ml at 2 ml/sec by high-pressure pump and scanning immediately after the end of injection. Remember the site of any compressive lesion will be at or above the clinical level, never below it, and so as a general rule scan the whole spine or at least six spinal segments higher than the presumed site of pathology.

Resolution: standard

Filter: soft tissue in first acquisition with post-reconstruction with bone filter

Table 13.4 Basic parameters for spinal CT

Patient position	Supine
Surview	Dual surview if possible,
	AP and lateral
First slice	Top border of vertebra above area of interest
Last slice	Lower border of vertebra below area of interest
Field of view	˜250 mm
Slice width	0.9 mm
Slice increment	0.45 mm
Pitch	0.875
Collimation	64 × 0.625 mm
Rotation time	1.5 sec
kV/mAs	120 kV/350 mAs
	If looking only for bony injury mAs can be kept low, i.e. 150 mAs
Resolution	See notes for examination required
Filter	See notes for examination required
Reconstructive zoom	As appropriate to include vertebral bodies
Windowing	WC 250
	WW 1500 or other bone windows
Contrast	See notes for examination required

13.3 AP (A) and lateral (B) surviews for a thoracolumbar study. (C) Sagittal MPR. CT mylogram of a patient with clinically severe cervical myelopathy; a pacemaker precluded MR.

CT myelography

Contrast: intrathecal contrast via lumbar or cervical puncture, e.g. 5 ml 300 mgI% of contrast licensed for intrathecal use.

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