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RAD 203 CT
Terms in this set (90)
The image produced is transaxial or tranverse. It makes computer reconstructed sagittal and coronal images possible
AKA conventional tomography. The plane image is parallel to the long axis of the body resulting in sagittal and coronal images.
The part of CT scanner that houses the x-ray tube, cooling system, detector assembly, and the data acquisition system. Referred to as "doughnut"
Hounsfield Unit/CT number/X-ray attenuation coefficient
a) -1000 is air
b) -100 is fat
c) 0 is water
d) +40 is grey matter
e) +1,000 to +3,000 is dense bone
the level of brightness of each pixel displayed on monitor
occurs when transverse images are staked to form 3-D data set.
when source-detector assembly makes one sweep across the patient/internal structure
Math formula used to carry out complex calculations required for image reconstruction. Also used for enhancing soft tissue, bone, and edge resolution
An arrangement of cells in rows and columns.
A 512 x 512 matrix has 264,144 individual cells of information
Pixel( Picture Element)
Individual cells in an image matrix.
2-D representation of a corresponding 3-D tissue volume.
Determined by multiplying the pixel size by the thickness of the CT image slice.
FOV(Field of View)
Area of anatomy displayed by the CRT(Cathode Ray Tube)
As matrix size increases for FOV,
pixel size decreases
As the FOV of a pixel matrix size is increased,
pixel size increases proportionately
represents the transverse or horizontal plane.
It transects the body from side to side.
Divides the body into superior to inferior portions
Longitudinal plane dividing the into anterior and posterior portions
CT Image Appearance
Bones and other dense materials, white.
Air and lower-density material, black.
fat, muscle, and organs, various shade of gray.
has 8 bones
Referred to as "anchor bone of the cranium"
has two sets of wings: greater and lesser
projects inferiorly from the body of the sphenoid and forms the posterior walls of the nasal cavity.
has 14 bones
found in the medial wall of the orbit b/n maxilla and labyrinth of the ethmoid bones
forms the inferiolateral walls of the orbits
Inferior Nasal Conchae
Scroll-shaped bones found in the nasal cavity
forms inferior portion of the bony nasal septum
originates at C6 and bifurcates into right and left main bronchi at T4-T5
known as the last cartilage ridge of the trachea
divided into superior and inferior lobes by an oblique fissure
originates at C6 as posterior continuation of the pharynx
Rotator Cuff consists of
- teres minor
extends from the greater curvature of stomach and transverse colon to blanket the anterior surface of abdominal organs
lies inferior to the left hemidiaphragm and posterior to the fundus of the stomach. Belongs to the lymphatic system.
approximately 8 feet long occupaying the left upper abdomen
lies transversely across the abdomen at level of L-2
passes through the diaphragm at the level of T-11. At L-11 the abdominal aorta bifurcates to form right and left common iliac arteries
first CT system was commercially marketed for clinical use
components necessary to construct a CT imaging system were already available to medial physicists.
Hounsfield and Cormack are given credit for development of CT
Godfrey Hounsfield first demonstred the CT technique, while employed by EMI, Ltd.
Alan Cormack shared the Nobel Prize in physics with Hounsfield
required 180 translations in 1 degree increments
one image took "5 minutes" to complete
fan-shaped beam. Used 10 degree increments with 18 translations. Designed for imaging times of "20 seconds" or longer for each translation
views the entire patient at all times and can produce an image in less than "one second"
caused by a single detector, or multiple detector malfunction resulting in a ring on the reconstructed image.
uses fixed circular array of detectors containing as many as 4,000 individual elements.
Imaging time less than "one second"
Free of ring artifacts
a CT imaging system can have 2-3 consoles
as many as 250,000 equations are solved simultaneously.
Two main components of computer
- microprocessor(CPU): processes information
- primary memory(RAM): a form of active storage
Optical disks or
laser disks are removable disks
Scintillation crystal-photomultiplier tube assembly
made up the early scintillation detector arrays. Require a power supply for each PMT
Scintillation crystal-photodiode assembly
converts light into electrical signal, is smaller and cheaper, and does not require its own power supply.
Types of scintillation crystals included Sodium iodide
used in earliest imaging system, but replaced by Bismuth germinate and cesium iodide
the current crystal of choice in Detector Array
Two types of Collimator in CT
- PREPATIENT collimator
- PREDETECTOR collimator
approximately 50kW power is necessary for a multi-slice unit
Support Couch or Table weight limits
varies from 300 to 600 lbs
electromechanical devices that conduct electricity and electrical signals through rings and brushes.
Slip rings makes Spiral CT possible because
it allows the gantry to rotate continuously without interruption
Shaded Surface Display(SSD)
Image is called "volume rendered"
determined by 5 principle characteristics:
1- spatial resolution
2- contrast resolution
5- spatial uniformity
the ability to distinguish one soft tissue from another without regard for size or shape
- the smaller the pixel, the better the spatial resolution
- the thinner the slice, the better the SR
if all pixel values were equal, noise would be zero.
noise should be evaluated_____ through imaging a 20-cm-diameter water bath
Noise depends on
kVp and filtration pixel size, slice thickness, detector efficiency, patient dose(# of x-ray used by the detector to produce the image, ultimately controls noise)
180 degree(one half revolution) separation of values is desired to prevent blurring
the relationship between patent couch movement and the x-ray beam width. Expressed as a ration, usually in mm
results in overlapping images and higher patient dose
results in extended imaging and reduced patient dose
ONE Advantage of multi-slice CT
increasing pitch above 1:1 increases the volume of tissue imaged at a given time
Multi-slice Detector Array
use several parallel detector arrays, commonly 4, containing thousands of individual detectors. Capable of 320 image slices simultaneously and can combine two adjacent arrays for wider slice imaging
20 cm water bath should be imaged daily
Should be within +/- 10 Hounsfield Unit of zero
average value for water
should be within +/- 10 HU from center periphery
- tested semi-annually
- assessed using AAPM five-pin insert test
- coefficient of correlation at least0.96% or 2 standard deviations
most important of the QC program because it ensures proper performance of the detector array
- tested semi-annually to manufactures's specifications
- most medical physicists use bar pattern or hole pattern
- tested semi-annually
- system should be able to resolve 5mm objects a 0.5% contrast
- tested semi-annually
- within 1 mm of intended slice thickness for 5 mm or greater
- within 0.5 mm for less than 5 mm
- the automatic maneuvering of the patient though the CT gantry should be tested MONTHLY
- measurement should be within +/- 2 mm of intended couch movement
- tested semi-annually
- done same time as couch incrementation
- No recommended limits are specified
- tested semi-annually or after x-ray tube replacement
- with fixed technique, should be within +/- 10% from one assessment to the next
- specified as CT Dose Index(CTDI)
CT accounts for 70% of total patient effective dose
U.S. Public Health Service data
suggests that 10% of all x-ray exams are CT
Entrance Skin Exposure(ESE)
referred to as patient dose, and is higher in CT than other x-ray procedures
- CT uses a fine, collimated beam of x-ray
- scatter radiation is reduced significantly
- contrast resolution is improved significantly
-approximately 50% ESE for body CT
Multi-slice vs Conventional CT
- at higher pitch, dose in multi-slice reduced
- at lower pitch, dose in multi-slice is higher
- patient dose in CT is proportional to the x-ray beam intensity and to the average beam energy
- head imaging is 3,000-5,000 mrad (30-50 mGy)
- body imaging is 2,000-4,000 mrad (20-40 mGy)
increases patient dose and width has the same effect as noise
Body imaging is
2,000-4,000 mrad (20-40 mGy)
Recommended textbook explanations
Introduction to the Theory of Computation
Computer Organization and Design MIPS Edition: The Hardware/Software Interface
David A. Patterson, John L. Hennessy
Introduction to Algorithms
Charles E. Leiserson, Clifford Stein, Ronald L. Rivest, Thomas H. Cormen
Operating System Concepts
Abraham Silberschatz, Greg Gagne, Peter B. Galvin
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