Advanced Imaging and 3D Printing Flashcards
In conjunction with myelography, CT can be used to?
Assess spinal cord compression
Can you think of any disadvantages of using CT over other imaging modalities?
Heavy sedation/GA
Poor spinal cord differentiation
Poor Infratentorial detail
What does a CT struggle to differentiate with the spinal cord?
Grey vs white matter
Contrast CT studies
What medium?
A water-soluble intravenous contrast medium
Contrast CT studies:
How much is used?
2ml/kg body weight
What is the max amount of contrast to be used for contrast CT?
60mls
Contrast CT - ionised or non ionised?
Either can be used
What will injection of contrast show with contrast CT?
areas of damage to or changes in the integrity of vascular endothelium or blood-brain-barrier.
How can damage be seen with contrast CT?
Leakage of contrast
Contrast can be used for assessment of compressive spinal cord lesions by performing a CT-myelogram. The same volume as for a myelogram with radiographs should be used (A?) but the contrast should be diluted to B)
A) 0.2-0.3ml/kg body weight
B) 1 in 10 parts
In cases of ? (2) plain CT may provide the necessary information for diagnosis
mineralised disc extrusions
haemorrhage
MRI is superior to CT for the evaluation of (5)
muscle,
tendons,
intervertebral discs,
spinal cord
cerebral parenchyma.
High-field-strength MRI units provide better A) (2) resolution and allow more accurate interpretations than low-field-strength units.
A) spatial and contrast
Can you think of any disadvantages to using MRI? (5)
- Financial
- Interpretation
- GA needed
- Time consuming
- No metal in vicinity
CARE interpreting MRI - why?
Highly sensitive and non-significant lesions can be found
Ultrasound can also be performed postoperatively (e.g., after hemilaminectomy) to check for possible remaining?
Disc material
In cases of suspected ? abdominal ultrasound can be used to evaluate the presence of a liver shunt (portosystemic shunt)
Hepatic encephalopathy
U/S can be used for confirmation of A) (scanning via persistent fontanelles,) or B) e.g., within the brachial plexus or for intraoperative identification of intramedullary lesions.
A) Hydrocephaluc
B) Soft tissue masses
Scintigraphy is an imaging modality only available at specialised centres. It is useful in cases of? (2)
Non-localised pain or multifocal diseases
How does scintigraphy work? What is highlighted?
A radiopharmaceutical agent is injected to highlight areas where the blood-brain-barrier has broken down or fails to exclude the injected radionucleotide. Lesions show up as ‘hot spots’.
Vertebral screws and bone cement are used for the management of several conditions such as (4)
atlanto-axial instability (C1-C2 subluxation)
caudal cervical spondylomyelopathy (wobbler syndrome)
lumbo-sacral instability
vertebral fracture/luxation.
Pitfall of vertebral screw and bone cement
risk of violation of the vertebral canal with screw placement, compromising the intervertebral foramen and / or risking damage to the vertebral artery
With the broader availability of 3D printing and what software it is now possible to develop patient-specific drill guides for spinal pedicle screw placement
CAD (Computer Assisted Design)
What prep is needed for printed drill guides?
A CT scan of the affected vertebrae needs to be performed first. Using the DICOM images exported in the CAD software optimal screw size and orientation can be determined. Each of the vertebrae can be manipulated in all planes for accurate planning of bicortical pedicle screw placement and it also allows the screw size for each patient to be maximised.
Printed drill guides: The material used can vary depending on the printer and is usually made of?
biocompatible resin (methacrylate photopolymer resin).
With printed drill guides; once made what needs to happen before surgery?
Sterilise!
Advantage of printed drill guides? (6)
planning of the optimal screw trajectory prior to the surgery being performed.
Better fixation
Increased osteosynthesis strength
Reduce surgical time
Reduced morbidity
Another field of application of 3D printing in spinal surgery is the development of patient specific 3D printed implants printed on implantable polymers or titanium.
Where can these be used?
These implants can conform to or reproduce the part of the vertebral column that needs to be reinforced or replaced.
