# c-spine

Which of the following is the best explanation for why the lateral cervical spine projection needs to be performed with a 72-inch SID?1. It reduces magnification of the cervical spine
2. It prevents size distortion of the cervical vertebrae
3. It results in better spatial resolution of the cervical vertebrae
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Which of the following is the best explanation for why the lateral cervical spine projection needs to be performed with a 72-inch SID?1. It reduces magnification of the cervical spine
2. It prevents size distortion of the cervical vertebrae
3. It results in better spatial resolution of the cervical vertebrae
1, 2, and 3
In the lateral position, the patient's shoulders displace the spine away from the image receptor (IR) resulting in a large object-to-image receptor distance (OID). When there is a large OID, the resulting image will display size distortion in the form of magnification and this will result in reduced spatial resolution. To compensate for the large OID, SID must be increased to minimize size distortion and improve spatial resolution.
This is correct, no correction is needed.
If the teeth and base of the skull are perfectly superimposed the image cannot be improved upon, even if there is superimposition of the odontoid process. If the teeth are demonstrated over the tip of the odontoid, then the chin needs to be lifted to tilt the head up more and superimpose the lower margin of the upper incisors over the base of the skull. If the base of the skull is projected over the odontoid, then the head needs to be lowered more. Opening the mouth more would not fix the problem since only the lower jaw moves to open the mouth, leaving the upper teeth still in the wrong location.
Inferior margin of the thyroid cartilage.
When performing an AP axial projection of the cervical spine, the central ray should be angled 15-20 degrees cephalad. Because the central ray should pass through C4, and because there is a cephalic angulation of the beam, the central ray should enter inferior to the level where it exits. In this case, for the central ray to pass through C4, it will need to enter the anterior neck at the inferior margin of the thyroid cartilage.
45 degree patient rotation demonstrates elevated intervertebral foramina
The intervertebral foramina of the cervical spine open anteriorly at an angle 45 degrees from the midsagittal plane; they are directed inferiorly approximately 15-20 degrees. Posterior oblique cervical spine images (RPO, LPO) are performed with the patient rotated 45 degrees from the AP position. This positioning will demonstrate the elevated intervertebral foramina.
15 degree caudal angle.
The intervertebral foramina of the cervical spine open anteriorly at an angle 45 degrees from the midsagittal plane; they are directed inferiorly approximately 15-20 degrees. In order for the central ray to pass through the intervertebral foramina, the central ray should be directed 15 degrees caudad when performing PA obliques and 15 degrees cephalad when performing AP obliques.
Left anterior oblique
The intervertebral foramina of the cervical spine open anteriorly at an angle 45 degrees from the midsagittal plane; they are directed inferiorly approximately 15-20 degrees. Although not all protocol manuals use this method, to demonstrate the intervertebral foramina with minimal size distortion (magnification) the patient should be adjusted into the left anterior oblique position, putting the side of interest closest to the image receptor.
A 72 inch SID should be used when erect images are obtained
In order to compensate for the increased distance between the spine and the IR when performing oblique and lateral cervical spine images, the central ray should be adjusted to take advantage of the greatest SID. When positioning for a lateral image, the MSP of the head is parallel with the image receptor and the chin is slightly elevated to prevent superimposition of the mandible and the spine; because the patient's entire body is rotated 45 degrees for an oblique image, there will always be superimposition of the spine and mandible. The beam is perpendicular for a lateral image and angled 15-20 degrees for an oblique image.
1 only.
On the lateral projection, the bodies and spinous processes should be in profile with no rotation. The disc spaces will also be well demonstrated between the bodies. The transverse processes are not well visualized on the lateral, and the pedicles and intervertebral foramina are visualized only on oblique projections.
The patient's midsagittal plane (MSP) should be centered to the middle of the (IR).
The MSP divides the body into equal right and left halves; placing this plane in the center of the receptor will ensure that the spine is in the middle of the x-ray field and IR. For an AP projection, the top of the light field or 10x12 inch IR should lay at the top of the ears and the central ray should enter the patient at the inferior thyroid cartilage and exit at the level of C4.