Ct Flashcards
What is Dynamic CT?
The process of producing a cross-sectional image of the body using a collimated beam of radiation that rotates around the patient.
What is Enhanced CT?
The use of a contrast agent to improve the appearance of vessels or organs that are similar in density to the surrounding tissues.
Define Field of View in CT imaging.
The part of the scanned plane which may be included in the final image.
What does ‘Helical’ refer to in CT terminology?
Spiral.
What is Image Acquisition?
The collection of data in order to produce an image.
Define Image Format.
The process of storing an image on computer disk, magnetic tape, film, or on the World Wide Web.
What is Image Manipulation?
To digitally change the appearance of the acquired image in order to improve it.
Define Image Reconstruction.
The process of generating an image from raw data or a set of unprocessed measurements.
What does Isotropic mean?
Having the same properties in all directions, e.g., density.
What is a Matrix in the context of imaging?
The columns and rows that form a digital image.
What is Mean Window Level?
The average range of pixel values in an image.
Define Noise in imaging.
Anything that distracts from the information required on an image.
What is a Nutating Detector Ring?
When the detectors vibrate in such a way as to keep the detectors nearest the tube out of the way of the X-ray beam.
What does Pitch refer to in CT imaging?
The table movement during one complete rotation of 360° divided by the column width (or slice thickness).
Fill in the blank: A Pixel is a _______.
two dimensional ‘picture cell’ or ‘dot’ that makes up the image on a digital display screen.
What is a Profile in imaging?
Line of data.
Define Slice in the context of CT.
A section through the patient which is recorded when the X-ray tube and detector make one complete rotation.
What is Slice Interval?
The distance between reconstructed slices.
What does Spatial Resolution refer to?
The smallest part of an image that can be seen.
Fill in the blank: A Voxel is a _______.
three dimensional pixel.
What is a Window in imaging?
The range of colour (or grey) scale values displayed on a digital image.
What is Window Width?
The range of pixel values displayed in the digital image.
Define Gantry in CT.
A circular device for holding the detectors.
What is the function of the X-ray Tube?
A method of producing X-rays which are collimated so that they are aligned to a specific number of detectors.
What are Detectors in CT?
Solid state devices containing caesium iodide crystals which collect the amount of radiation transmitted through the patient.
What is the role of Photomultipliers?
A device for increasing the number of electrons produced from photons hitting a cathode.
What is a Photodiode?
A light-controlled variable resistance that allows current flow in direct proportion to the quantity of light it is exposed to.
Describe the Housing in CT machines.
A ‘doughnut’ shaped structure which contains the X-ray tube and the detectors.
What was the original movement mechanism in CT machines?
High tension cables wound round a drum, which were replaced with slip ring and brushes.
What is the purpose of the Table in CT?
For the patient to lie on and can move forward at a predetermined distance or at a constant speed.
What does the Operator Console allow?
Where the operator can determine the settings for the scan.
What is the Tomographic Principle?
The X-ray tube and detector move together and rotate around a set point, keeping that point in focus while blurring structures above and below.
What is a Narrow Window in imaging?
The grey is distributed over a narrow range of units centered around the average HU for the structure of interest.
What is a Wide Window in imaging?
The grey is distributed over a wide range of units centered around the average HU for the structure of interest.
What is high density tissue?
(Bone), absorbs the radiation to a greater degree, and a reduced amount is detected by the scanner on the opposite side of the body
What is low density tissue?
(Lungs) absorbs the radiation to a lesser degree, and there is a greater signal detected by the scanner
Why is contrast often used in CT?
° used to visualise the cardiovascular system (e.g. investigating for suspected aneurysms, dissections)
° used to identity whether a tumour is malignant
What does the density of body tissue determine?
The degree to which the X-rays are attenuated.in turn this affects the brightness and contrast of the imaged tissues.
How do diff. Attenuation coefficients look on a CT
° high #attenuation coefficient tissues ( strong absorption) show up white, and law attenuation coefficients (weak absorption) show up black. This is quantified by hounsfield scale of radiodensity tissues with a high household unit have a high attenuation coefficient so look while.
What are the household values for air, fat, water, blood and bone?
° air = - 1000
° fat = - 70
° water = O
° blood = 70
° bone = 1000
What is volume rendering?
Voxel HU’s are coded with colour and transparency
What is surface rendering?
Creates a one or more iso-surface (s) from voxels of same level.
Benefits of CT regarding medical management.
- determining when surgeries are necessary
- reducing the need for exploratory surgeries
- improving cancer diagnosis and treatment
- reducing the length of hospitalisations
- guiding treatment of common conditions e.g. injury, cardiac disease, stroke.
- Improving patient placement into appropriate areas of care, such as intensive care units
What are the principle advantages of CT?
- Rapid acquisition of images
- a wealth of clear and specific information
- a view of a large portion of the body
What are some of the basic components of a CT scanner?
- Gantry aperture (720mm)
- microphone
- sagittal laser alignment
- patient guide lights
- XR exposure indicator
- Emergency stop buttons
- Gantry control panels
- external laser alignment
- patient couch
- ECG gating monitor
