Midterm Flashcards
What are four appearances of artifacts?
Ring
Band
Streak
Shading
What is the start and end location for a CT routine chest?
Just above lung apices to Kidneys
Name two patient induced artifacts in CT?
Motion & Metal & Out of field
Name the two correction/remedy for ring artifacts in CT?
detector calibration
detector replacement
The only CT procedures that you have learned that is scan in Axial is?
Head
What is the definition of the term “slice” in relationship to CT?
One 360 degree rotation around the patient pieced together
What is the CT number for bone?
400 to 1000
What is the CT number for air?
-1000
What is the CT number for water?
0
What is the CT number for lung?
-200
Name the four step process of a conventional CT scanner?
1- start; tube and detectors are accelerated to const. speed
2- x-ray tube energized data collected for 360 degree
3-stop; tube and detectors slow down & stop
4-table & patient indexed to the next scanning position
What is the display field of view?
the area at which the tube is imaging
What is another name for a conventional CT scanner?
Slice by Slice scanner
Name two requirements for a Spiral/Helical CT unit
-Complete a full 360 degree rotation continually
-Table move through the gantry continuously
What is a pixel?
a 2 dimensional area of an image
What is a matrix?
rows and columns of pixels together
What are two advantages of a multi-slice CT scanner?
-Faster scan time- easier with single breath for patient
-Better spatial resolution
Name the three steps for formation of CT images by a CT scanner?
-Data acquisition
-Image resolution
-Image display
DII ARD FORM
Spiral CT was made possible because of what new technology?
Slipring technology
What are two important features of the gantry?
-Apperature
-Tilting of the gantry
Who was the person who developed the mathematics used to reconstruct the CT images?
Radon/Cormack
Name the generation scanner that used a rectilnear pencil beam?
1st gen
Name the generation scanner that used spiral?
6th gen
Name the generation that used rotate-rotate?
3rd gen
Name the generation that used translate rotate?
2nd gen
What is the purpose of the detectors?
To capture the beam to help create the image
Name the two types of collimators in a CT unit?
-Precollimator
-Predetector
What is the most significant development in radiology in the past 40 years?
CT
When does tomography trace back to?
1920’s
What does a CT scanner do?
Looks at a specific layer or section of the body
Conventional Tomography uses what type of tomography?
Axial
Computed Tomography uses what type of tomography?
Transverse image
How many major design advancements has Ct gone through since 1970’s?
5
What type of beam did the 1st generation CT scanner use?
pencil beam
How much did the 1st generation scanner rotate?
180 degrees
What kind of scan was the 2nd generation?
translate rotate
How much did the 2nd generation CT scanner rotate?
180 degrees
How many detectors did the 2nd generation CT scanner have?
5 to 30 detectors
What was special about the 2nd generation over the 1st generation?
It had a faster scan time
What kind of scan did the 3rd generation use?
Rotate-Rotate
What kind of beam did the 3rd generation use?
A fan beam of 30-60 degrees for full patient coverage
What happens in the 3rd generation if one detector fails?
A ring artifact appears
How much did the 3rd generation scanner rotate?
360 degrees
Why didn’t the 4th generation CT scanner last long?
-Cost of detectors
-Too much scatter given off
How did the tube rotate in 4th generation scanners?
Rotates around a stationary ring of detectors
What type of beam was used in the 4th generation scanner?
Fan beam
How many detectors did the 4th generation use?
8,000 detectors
What is the 5th generation scanner used for?
Heartscan
What was special about the 5th generation scanner?
Allowed for continuous rotation of the tube for spiral
The continuous motion made no interscan delay b/c as the tube moves the table moves
What made Spiral CT possible?
Slipring technology
What is another name for 6th generation scanner?
Spiral CT
What were benefits of Spiral CT?
-Less motion artifacts
-Improved lesion detection because the reconstructed image can be at arbitrary intervals
-Reduced scan time
-Advances in computer processing allows for multi-planar reconstruction and even 3D reconstruction
What are basic CT scanner components?
-Gantry includes the pedestal or table, tube, collimators, detectors, and high voltage generator
-Operators Console
-Computer
What are the three steps of the formation of CT images by a CT scanner?
1- Display Acquisition
2- Image Reconstruction
3-Image Display
DII ARD FORMATION
What is image acquisition?
Refers to the collection of x-ray transmission measurements from the patient
How many layers of laser are on the gantry?
3 layers
What is the tilt range for the gantry?
+/- 12 to +/- 30 degrees
Table weight limits vary from ____ to ____ lbs.
300 ; 600
What is Slice by slice data acquistion?
Conventional CT, the tube rotates around the patient to collect data from a single slice of tissue, followed by table moving so that the next contiguous slice can be scanned
What are the four steps of Interscan delay?
1- Tube must be accelerated to constant speed of rotations
2- Tube produces x-rays that are transmitted through the patient to fall on the detectors
3- patient resumes breathing while the tube slows down and comes to a stop
4- Unwind the cable so another 360 degree slice can be scanned
Is interscan delay in Spiral CT?
No, the scan stops and the patient moves
What are limitations of interscan delay?
-Longer exam times
-Omission of certain portions of anatomy b/c patient respiration phase may not be consistent
-Inaccurate generation of 3D images and multiplanar reformatted images, also from inconsistent levels of inspiration
How does Spiral-Helical CT work?
The tube rotates continuously around the patient
Why is Spiral Ct called Spiral CT?
The geometry describes a spiral or winding
The geometry of Spiral-Helical CT also is called? Why?
Spiral-helical Volume CT; It defines a volume of tissue
What are requirements for Spiral-Helical CT?
-Continuously rotating scanner based on slip ring technology
-Continuous table movement
-Increase load ability of the x-ray tube
-Spiral-Helical Algorithm
-Mass memory buffer to store the vast amount of data collected
-Increased cooling capacity of the x-ray tube
-Slip rings replaced the high tension cables and allowed for the continuous rotation of the tube
-Volume scanning, Spiral Helical Scanning are the same
What are advantages of Spiral CT?
-Multiplanar reconstruction
-Shorter scan times
-Artifacts reduced
When was multislice CT scanners announced?
1998
What were multislice CT scanners capable of?
Imaging four slices simultaneously per x-ray tube rotation
At the present time, multislice scanner are available to image how many slices per x-ray tube rotation?
320
What are the advantages of multislice scanners?
-Shorter acquisition time
-Decreased amount of contrast medium
-Improved spatial resolution
-Improved image quality
What is Raw Data?
The signal data from all of the detector responses and contain the most information for image production
What is another name for Raw Data?
Scan Data
What is Image Data?
Reconstructed data; The result of raw data undergoing computer computations and filtered back projection to produce the image
What is a matrix?
Grid formed from rows and columns of pixels
What is a pixel?
Two dimensional square picture element utilized toe display a digital image
What is a voxel?
A 3D cube of anatomy
What is a CT number/ Hounsfield number?
The number assigned that is related to the linear attenuation coefficient of the tissue within each voxel of the image
What is the CT number for fat?
-80 to -120
What is SFOV?
Area within the gantry from which the raw data are acquired
What is DFOV?
Determines how much of the raw data are used to create and image
What is ROI?
A display function available on all scanners defining and area on the image
What is algorithm?
set of mathematical calculations and processes applied in image reconstruction
What is the linear attenuation coefficient?
Numeric expression of the decrease in radiation intensity that follows transmission through matter
What is slice?
Section of the object that is being scanned
What are slip rings?
Devices that transmit electrical energy and allow continuous rotation of the x-ray tube for volumetric acquisition
What is volume scanning?
Refers to the acquisition of a volume of CT data, the patient moves through the gantry with uninterrupted rotation and output of the x-ray tube
What are indications for Head CT without contrast?
-Intracranial hemorrhage
-Early infarction
-Dementia
-Hydrocephalus
-Cerebral trauma
-Headaches
-Seizure
What are indications for Head CT with contrast?
-Mass
-Lesion
-AVM
-Aneurysm
-Metastasis
What ae indications for Chest CT with contrast?
-Infection
-Mass
-Emphysema
-Evaluation of abnormalities discovered on chest radiographs
-Evaluation of know or suspected congenital thoracic anomalies
-Evaluation of trauma
What are indications for Abdomen and Pelvis CT with contrast?
-Suspected abdominal mass
-Tumor staging
-Abscess
-Infection
-Pelvic mass
-Hematuria
-Renal Mass
What are indications of Renal stone study without contrast?
Suspected renal or ureteral calculi
What are indications for Cervical Spine CT?
Fracture or Dislocation
What are indications for Lumbar Spine CT?
Fracture or Dislocation
What are the scouts for Head CT?
AP & Lateral
What is the scan type for Head CT?
Axial
Where is the start and end location for Head CT?
Just below skull base (C1-C2)
Just above vertex
What are the window settings for Head CT?
-Soft Tissue
-Bone
What reconstructions are made for Head CT?
Sagittal & Coronal
How does the patient go in for Head CT?
Head first
What scouts are done for Chest CT?
AP & Lateral
What is the scan type for Chest CT?
Helical
Where is the start and end location for Chest CT?
Just above lung apices
To top of kidneys
What are the window settings for Chest CT?
Soft Tissue & Lung
What reconstructions are made for Chest CT?
Sagittal & Coronal
How does the patient go for Chest CT?
Goes in feet first with arms over head
What scouts are done for Abdomen & Pelvis CT?
AP & Lateral
What is the scan type for abdomen & pelvis CT/
Helical
Where is the start and end location for abdomen and pelvis CT?
Just above Diaphragm
Just below Symphysis pubis
What Contrast is used for abdomen and pelvis CT?
Iv and Oral
What are the window settings for abdomen and pelvis CT?
Soft Tissue
Lung
Liver
What reconstructions are made for abdomen and pelvis CT?
Sagittal & Coronal
How does the patient go in for abdomen and pelvis CT?
Goes in feet first with arms over head
What scouts are done for renal stone studies?
Ap & Lateral
What scan type is renal stone studies?
Helical
Where is the start and end location for renal studies?
Just above diaphragm
Just below Symphysis Pubis
Why don’t you use contrast for renal stone studies?
Both stones and contrast appear white; making it difficult to see a stone
What are the window settings for renal stone studies?
Soft Tissue
What reconstructions are made for renal stone studies?
Sagittal & Coronal
How does the patient go for renal stone studies?
feet first with arms over head
What scouts are done for Cervical Spine CT?
Ap & Lateral
What is the scan type for Cervical Spine CT?
Helical
Where is the start and end location for Cervical Spine CT?
Just below Skull base (C1-C2)
Middle of T2
What are the window settings for cervical spine ct?
Soft Tissue
Bone
What reconstructions are made for Cervical Spine CT?
Sagittal & Coronal
How does the patient go for Cervical Spine CT?
Head first
What scouts are done for Lumbar Spine CT?
AP & Lateral
What scan type is Lumbar Spine CT?
Helical
Where is the start and end location for Lumbar Spine CT?
T12
S1
What are the window settings for Lumbar Spine CT?
Soft Tissue
Bone
What reconstructions are made for Lumbar Spine CT?
Sagittal & Coronal
How does the patient go for Lumbar Spine CT?
Feet first
What is an artifact?
Any discrepancy between the CT numbers represented in the image and the expected CT number based on the linear attenuation coefficient
What are the 4 appearances of artifacts?
-Streaks
-Band
-Shading
-Rings
What are sources of artifacts?
-Patient
-Imaging Process and Equipment
What are patient induced artifacts?
-Motion
-Metal Artifacts
-Out of field artifacts
Motion artifacts are caused by?
Voluntary and Involuntary Motion
What is the remedy for voluntary motion? involuntary motion?
voluntary: explanation of procedure and good communication
involuntary: short scan time
How does metal artifacts manifest itself?
Start Streaking
What is the remedy for metal artifacts?
-Removal of external metallic objects
-Mar Software
-Gantry angulation
What is out of field artifact?
Patient is not entirely enclosed in the scanning field of view
What is the remedy for out of field artifacts?
-Selection of larger SFOV
-Taping patient tissue
-Raising patients arms above their head on the scan of chest and abdomen
What are equipment imaging process artifacts?
-Ring
-Line in Topogram
-Staircase
What is ring?
Malfunction of a detector in a third generation scanner
What are the remedies for ring?
-Detector calibration
-Detector replacement
What is Line in Topogram?
Bad detector causes continuous line on the topogram
What is the remedy for Line in Topogram?
Detector Replacement
What is staircase?
Improper selection of slice thickness and slice incrementation when generation MPR and 3D images
What is the remedy for staircase?
-Thin Slice use
-50% overlap on recon slice incrementation
