CT Flashcards
CT
-multiple 2D, slice-like images (each millimeters in size) formatted in multiple imaging planes to display 3D images in various formats
hounsfield units
-A CT image is composed of a matrix of thousands of tiny pixels
-each is computer-assigned a CT number from –1000 to +1000 measured in Hounsfield units (HU) , after Sir Godfrey Hounsfield
-Density of tissue determines amount of Hounsfield units (denser structures absorb more energy)
-Air = -1000, Fat = -40 to -100 HU, Water = 0, Soft tissue = 20 to 100 HU, -Bone = 400 to 600 HU -> bone absorbs contrast
timing
4th/5th generation CT scanner:
2s-10s per slice -> every time donut comes around
-2-5ml SA: iodinated contrast
-continuous rotation
-abdomen: takes 30s
multiplanar reformation
Technique of overlapping images + reformat to see structures in different planes
-single acquisition
-For Maximum Intensity Projection:
-CT Angiography
-Cardiac Imaging
-more specialized = more contrast
-allergies to iodine, renal function (filtered by kidneys)
MPR is a technique that uses overlapping images from a single acquisition to reformat them, allowing for better visualization of structures in different planes. This is particularly useful for applications like CT Angiography and Cardiac Imaging, where maximum intensity projection (MIP) can highlight vascular structures with higher contrast, taking into consideration patient factors such as allergies to iodine and renal function.
abnormalities on CXR -> CT indication
Evaluate abnormalities on CXR
- Confusing shadows on plain x-ray
- Pts with pneumonia not responding to therapy
- Empyema verses abscess, evaluation of pleural Effusions
- Pulmonary nodules – new or follow up
- Interstitial lung disease
- Lung/Hilar/mediastinal masses
Negative CXR with clinical suspicious pathology
Staging and follow up malignancies
Evaluation vascular abnormalities ( PE, AA)
-Trauma
-Performance CT guided interventional procedures
multislice CT scanners permit very fasting imaging
-(head to toe in less than 10 seconds)
-development of new applications for CT (7th generation)
-virtual colonoscopy
-virtual bronchoscopy
-cardiac calcium scoring
-CT coronary angiography
-these are controlled elective setting
CT hazards and disadvantage
-Radiation to patient
-Requires computer processing power (expensive scanner)
-Portable CT Scanners
-Need space dedicated to its installation, and sophisticated
CONTRAINDICATIONS: NONE***
patient considerations
Claustrophobia
Cooperation
Size & weight restrictions
- upper weight limit ~450lbs
Allergy to iodinated contrast agents -> you can still do it but need to make sure its done in controlled (non acute) setting
terms for anatomic definition
-Chest CT scans are usually “windowed” and displayed in at least 2 FORMATS*
-ex. if looking for pleural effusion -> look for lung window -> changes gray scale so you can see it better
-bone window- fracture
-Windowing AKA “grey-level mapping”: contrast enhancement.
-process in which the CT image greyscale component of an image is manipulated to highlight particular structures.
Post-processing
-“Post-processing” allows for additional manipulation of the raw data
Benefits:
-demonstrate pathology
-without repeating a study
-Without radiation re-exposure to the patient
Post-processing refers to the additional manipulation of the raw CT data after the initial images are generated. This can include generating 3D reconstructions, applying filters to enhance certain features, or using advanced techniques like multiplanar reformation (MPR) to view the anatomy in different planes.
what type of window
Bone
what type of window
Mediastinal
what type of window
lung
What are all the windows
BLM BSA:
Bone
lung
mediastinum
brain
soft tissue
abdomen
Windowing = grey-level mapping contrast enhancement
- adjusts the display settings of the CT images to emphasize specific types of tissue, making it easier to diagnose various conditions
Orientation:
- patient is scanned in the SUPINE position.
- The patient’s right is on the viewer’s left, and the patient’s left is on the viewer’s right, which is a standard convention in medical imaging to maintain consistency.
- top of each image is the anterior (front)
- bottom is the posterior (back) part.
label
label
