Module 8, Year 1 - Radiology Flashcards
What is the anode heel effect?
Greater x-ray absorption occurs at the anode (+) side, thin part toward anode and and atlas at anode
What primarily controls density on a x-ray?
mAs - increasing mAs increases quantity of photons reaching film, increasing density
What makes a x-ray appear darker?
Increasing mAs
If a x-ray film is too light or too dark, what is the rule to change it?
Change mAs by a factor of 2
Inverse square law
The intensity of the x-ray beam is inversely proportional to the square of the distance of the object from the source. In other words, there is a rapid decrease in intensity as the beam spreads out over an increasingly larger area
T or F: KVP fine-tunes the density of the x-ray film.
False, KVP does NOT change the density of the x-ray film.
How does KVP affect the x-ray film?
Increases the contrast, short scaling, or creating more black and white (less detail)
OR
Decreases contrast, long scaling, or creating more grey (more detail)
What is the 15% rule?
If you want to double density, 2x mAs and increase kvp by 15%. If you want to half density, 1/2 mAs and decrease kvp by 15%.
How would you adapt a film for children or the elderly?
Decrease exposure by 30%
Why collimate?
Decreases radiation dose, scatter and density; while increasing the contrast
What does ALARA mean?
Keep radiation “as low as reasonably possible”
Do x-rays accumulate in the body?
No, x-rays do not make you radioactive, but the effects of exposure can accumulate.
What is OID?
The object to image receptor distance (OID) is the distance between the object to the detector.
OID is directly proportional to size distortion.
What is SID?
The source image receptor distance (SID), is the distance of the tube from the image receptor, affecting magnification. The greater the SID, the less magnification the image will suffer.
The SID is inversely proportional to size distortion.
What is the best way to avoid shape distortion?
Proper equipment alignment and patient positioning
What is dynamic range?
The ability of the detector to respond to change in exposure.
What is basilar invagination? What are some ways to determine if someone has this?
Upward displacement of the vertebral elements into the normal foramen magnum with normal bone - upward migration of the upper cervical spine.
McRae's Line McGregor's Line Chamberlain's Line Digastric Line Bimastoid Line
What are common causes of invagination?
Deformity (whether genetic or acquired) or softening of the bone at either the occipital bone or upper neck, esp. the dens.
Describe Chamberlain’s Line
Line joining the back of the hard palate with the opisthion
If dens is more than 3mm above this line, basilar invagination is suspect
Describe McRae’s Line
Line joining opisthion and basion
If dens is less than 5mm away from this line, basilar invagination is suspect
Describe McGregor’s Line
Line between hard palate and the most caudal point of outer table of occiput - only used when the opisthion is not available
If the tip of dens lies more than 4.5mm above this line, basilar invagination is suspect
Describe digastric line
Line drawn between right and left digastric grooves.
Tip of dens and atlanto-occipital joint normally project 11mm and 12mm below this line.
Basilar invagination is suspect when the dens is at or above this line.
Describe bimastoid line
Line between tips of the mastoid processes
Basilar invagination is suspect if the tip of dens projects above 10mm
What is Platybasia/Flat Skull Base/Martin’s Anomaly?
Developmental anomaly (or acquired deformity) of the skull in which the base of the posterior cranial fossa bulges upward; seen as flattening angle between clivus and body of sphenoid.
Determined by basilar angle, measuring greater than 143 degrees.
Describe the basilar angle
Angle from lines connecting nasion to mid-sella, and mid-sella to basion
Normal: 125-143 degrees
Platybasia: >143 degrees
Basilar kyphosis: <125 degrees
Modified MRI technique for the basilar angle extends line across the anterior cranial fossa to the tip to the dorsum sella and line along posterior of clivus
Adult normal: 116-118
Children normal: 113-115
What congenital conditions predispose someone to platybasia?
Achondroplasia Down Syndrome Chiari malformations Craniocleidodysostosis Craniofacial anomalies Osteogenesis imperfecta
What conditions may lead to acquiring platybasia?
Paget Disease Osteomalacia Rickets Trauma Fribrous Dysplasia Hypoparathyroidism
Describe a normal sella turcica
No more than 12mm craniocaudal and 16mm anterior-posterior
ADI normals
<3mm adults
<5mm children
A practice member’s x-ray shows a “V-shaped” atlantodental interval space. She states she was in a car accident a few months ago and had a concussion. What may be suspect?
Transverse ligament instability
Describe the cervical gravity line
Line drawn vertically from tip of dens should intersect C7 vertebral body
Describe horizontal and angular instability
Difference in the angles formed by the intersection of lines extended from the endplates of two contiguous vertebrae
Each segment should NOT be greater than 11 degrees
The accumulated measurement between C3-C4 and C4-C5 parallel endplate lines is 29 degrees. What does this suggest?
Horizontal and angular instability
Describe Clinical Instability
Pathological state of motion at an intervertebral level in the cervical spine that results in clinically intolerable symptoms (like root and cord damage) requiring prolonged bracing or surgery
What better shows instability Flex/Ext x-rays or CT/MRI?
CT/MRI
Describe the cervical lordosis depth method
Line from tip of odontoid to posterior surface of C7
Average: 12mm
Negative value: kyphosis
Larger value: hyperlordosis
Smaller value: hypolordosis
Describe cervical lordosis angle (Cobb)
Angle between lines centered through anterior and posterior tubercles of C1 ad across the inferior endplate of C7
Normal: 40 degrees
Describe Harrison posterior tangent method
Angle measurement between intersection of C2 posterior body line and C7 posterior body line
Smaller standard of error measurement than Cobb angle
Normal range: 31-40 degrees
Describe healthy prevertebral soft tissue thickness on x-ray
Adults only: 6mm at C2 and 22mm and C6
Kids: 7mm at C2 and 14mm at C7
Adults: 7mm at C2 and 21mm at C7
Generally, the prevertebral soft tissue increases with flexion and decreases with extension.
Normal spinal canal measurements on x-ray
C2: 16mm C3: 14mm C4: 13mm C5: 12mm C6: 12mm C7: 12mm
What is a significant finding on George’s Line?
Anything greater than 3mm, 3.5mm or more is permanent damage
Describe Grabb-Oakes Line
Tip of basion to posterior inferior C2 vertebra
Normal: 9mm or less
Anything higher than 9mm suggests ventral brainstem compression
Describe the clivoaxial angle
Clivus to basion and another line drawn long the posterior margin of the dens
Normal: 150-180
< 135 degrees is “potentially pathological”
What measurement assesses the degree of basilar invagination?
Clivoaxial angle
Describe Harris Measurement
Measurement from the tip of the clivus to either the tip of the dens or 90 intersect with posterior axial line
12mm or greater indicates occipitoatlantal disassociation
Describe Power Ratio
Calculated by dividing the distance between the tip of the basion to the spinolaminar line by the distance from the tip of the opisthion to the midpoint of the posterior aspect of the anterior arch of C1
> 1 = vertical distraction
<0.55 = posterior disassociation
Describe condyle-C1 interval
Interval between Condyle and C1 at 4-equidistant points on the joint surface in sagittal and coronal reconstructions of computed tomography
*Been shown to provide the highest diagnostic accuracy for pediatric patients
Describe Lee x-line
The first line connects the basion to the midpoint on the C2 spinolaminar line (the anterior aspect of the posterior ring of C2) - should tangentially intersect across the superior posterior aspect of dens
The second line connects the opisthion to the posteroinferior edge of the body of C2 - should tangentially intersect just anterior the posterior ring of C1 (the highest edge of the C1 spinolaminar line)
What would indicate a significant finding when evaluating the APOM lateral masses?
2mm or greater overhang of atlas over axis superior articular facet.
This could indicate Jefferson fracture, odontoid fracture, alar ligament instability, rotatory atlantoaxial subluxation (and possibly spondyloschisis)
Generally, <2mm is okay
Describe a child’s psuedo-jefferson fracture
Children up to 4 years old may have an overhang of the atlas over the axis superior articular facet and it be a normal variant due to accelerated growth of atlas (pseudo-spread)
Describe Swischuck line and child’s psuedo-anterolisthesis
Anterior aspect of posterior arch of C1 –to- anterior aspect of posterior arch of C3
The anterior aspect of posterior arch of C2 should be within 1-2mm of this line. <2mm is a pseudosubluxation, but this does not rule out a hangman fracture
> 2mm indicates a true subluxation
When is it appropriate to take an image?
When the data gained from the test will influence patient care. (All or nothing approach is NOT advisable)
A practice member has has acute rheumatoid arthritis. Adjust?
No dynamic thrust
A practice member was in a car wreck. The x-ray makes you suspect of instability. Adjust?
No dynamic thrust
A practice member has sacral ankylosing spondylitis. He states he has been adjusted manually before. Adjust?
No dynamic thrust
There is excessive movement on the flexion/extension film. The practice member states he had a fracture in his neck years ago, but it has healed. Adjust?
No dynamic thrust
A tilted APOM shows movement of the os odontoideum. The practice member states she has never had any heavy trauma to the head. Adjust?
No dynamic thrust
Metastasis is see on the x-ray. Adjust?
No dynamic thrust
A practice member has suspected Paget’s disease. Adjust?
No dynamic thrust on the suspected segment.
Practice member states she has had tingling bilaterally in her arms and legs. Adjust?
No dynamic thrust in either the cervical or lumbar regions.
A practice member is suspect of vertebrobasilar insufficiency syndrome. Adjust?
No dynamic thrust.
Practice member has an MRI showing pooling of the jugular vein bulb. Adjust?
No dynamic thrust to the atlas bone.
What are some relative contraindications of adjusting with a dynamic thrust?
Articular hypermobility (when stability of joint is uncertein)
Severe demineralized bone
Benign bone tumors
Bleeding disorders and anticoagulant therapy
Radiculopathy with progressive neurological signs
A practice member was in a car wreck. The x-ray makes you suspect of instability. Adjust?
No dynamic thrust
Name any of the spine trauma and x-ray criteria
Back pain
Midline tenderness on palpation
Distracting injury or other high risk mechanism
Neurological deficits
Altered consciousness: head trauma, ethanol/intoxication, drugs