Chapter 71 - Computed Tomography Flashcards
What distinguishes CT from radiographs in terms of imaging capability?
CT has superior contrast resolution
What is the primary limitation of CT use in equine practice?
Need for general anesthesia
What is the approximate diameter range of CT gantry openings?
50 to 85 cm
What technology is expanding the scope of CT imaging in horses?
Cone beam imaging (CBI)
What is an important consideration for CT image quality?
Adequate gamma ray count density
Why is familiarity with specific algorithms important in CT imaging?
To optimize image quality based on the structure being imaged
What feature of helical CT scanning improves its efficiency?
Continuous rotation of the gantry
What is a characteristic of single-slice CT scanners regarding slice thickness?
Altered by opening or closing a collimator
How do multiple-detector array scanners improve upon single-slice CT scanners?
Through faster data acquisition and reduced tube heating
What affects the contrast and spatial resolution in a CT scan?
The choice of slice thickness
Why are thinner slices preferred in certain CT scans?
They improve spatial resolution and reduce partial-volume averaging
What is the purpose of using Hounsfield units in CT imaging?
To crudely determine tissue type and contrast-medium enhancement
Which artifact in CT imaging is caused by changes in the intensity of the x-ray beam?
Beam hardening
What issue can arise from the partial volume effect in CT scans?
Misinterpretation of tissue types within a voxel
How can motion artifacts affect CT images?
By leading to blurring or double images
What specific problem does the equine caudal fossa present in CT imaging?
Beam hardening and partial volume artifacts
The basic components of the CT scanner are
the image gantry **
- x-ray tube
-x-ray detector
- data-acquisition system
and the CT table**
certain helical system it is the gantry that moves and not the table
the image is reconstructed using a technique called
filtered back projection
what is the best algorithm for hard tissue and soft tisse?
For soft tissue imaging, a low-frequency or soft tissue algorithm is more appropriate to maximize contrast.
Figure 71-2. The same CT image of a horse with an intermandibular soft tissue sarcoma, but reconstructed with different algorithms and displayed with different window/level settings. (A) Transverse image reconstructed with a soft tissue algorithm, and displayed with a soft tissue window/level. (B) Transverse image of the same horse, reconstructed with a bone algorithm, and displayed with a soft tissue window/level. Note that the image in (A) has a smoother appearance to the soft tissues with less graininess as the soft tissue algorithm reduces noise. (C) Transverse image reconstructed with a soft tissue algorithm and displayed with a bone window/level. (D) Transverse image reconstructed with a bone algorithm and displayed with a bone window/level. Note that the image in (C) has a more blurred appearance compared with (D), with decreased spatial resolution and detail of bony structures.
helical scanning is much ___________(faster/slower) and is appropriate for scanny any ________ (large/small) area
Helical scanning is much faster and is appropriate for scanning any large area or for angiographic studies.
How can the choice of slice thickness impact CT scan results?
Thicker slices increase signal and inherent contrast, while thinner slices improve spatial resolution
What causes metallic artifacts in CT imaging?
Presence of metallic implants within the imaged anatomy
What is the primary use of contrast media in CT scans?
To assess tissue perfusion
What is recommended before a postcontrast CT scan of the distal limbs?
A time delay of at least 5 minutes
How is CT angiography typically used in equine medicine?
To highlight the vasculature of the equine foot
What is a consideration for CT fistulography in terms of contrast medium?
Dilution with saline or sterile water is advised
What advantage does CT-dacryocystography offer?
It allows evaluation of the nasolacrimal system
the image is composed of pixels each one representing a
volume, or voxel of tissue
How does the window width and level affect CT image viewing?
. It adjusts the grayscale to highlight different structures
Specific tissues have characteristic levels of attenuation and measurement of the Hounsfield, what is it for?
Specific tissues have characteristic levels of attenuation and measurement of the Hounsfield units can therefore be used in part to crudely determine tissue type (fluid versus soft tissue) and to measure levels of contrast-medium enhancement.
What are the CT aritifacts?
Beam Hardening
Partial volume
Motion artifacts
Metallic artifacts
What is the purpose of multiplanar reconstruction (MPR) in CT imaging?
To reconstruct images in multiple two-dimensional planes
what is the dosage of constrat?
A dose of at least 200 mL of 300 mg/mL iodinated contrast medium is recommended and typical dosages of no more than 600 mL are used, primarily owing to the use of 60 mL syringes.
what is the way to adminster?
This large dose can be given as a bolus and should be administered through two jugular catheters to help optimize contrast medium enhancement.
what is a partial volume artifact?
how can you reduce the partial volume artifact?
Acquisition with thin slices that are reformatted as thick slices for viewing can help reduce the problem.
CT studies are viewed using different window widths and levels to highlight different types of structures. The window level refers to the
Hounsfield number around which the other shades of gray are centered.
For soft tissue viewing the Hounsfield number should be about
50
For bone viewing the Hounsfield number should be about
500
How many shades of gray can the human eye see?
30 to 90
How many shades of gray has the CT
typically 4096
what is multiplanar reconstruction (MPR)
referred to as multiplanar reconstruction (MPR), which allows reconstruction of a two-dimensional image in any plane. Sagittal, dorsal, and oblique plane reconstructions aid in defining the location and specifications of a lesion.
The quality of multiplanar reconstruction is dependent on
The quality of the reconstruction depends on the slice thickness used for acquisition and the use of helical or axial modes. Thinner slices always produce a smoother reconstruction with better spatial resolution in the selected planes (Figure 71-9)
Three-Dimensional Volume Rendering what is it?
3D volume rendering can be a very important tool in surgical planning (Figure 71-11). It allows visualization of the anatomy in a life-like perspective, and it can be used to understand lesion orientation
