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Unit 3 - RAD 121

Imaging 3 Objectives

Define spatial resolution. Ability of imaging system to produce separate images of closely spaced small objects. How well system images adjacent small structures such as edges or borders of structures that appear in hairline fx. Geometric variable - SHARPNESS.
Define recorded detail. The degree or amount of geometric sharpness of an object recorded as an image. radiographic detail - definition, sharpness
Define visibility of detail. ability of observer to see recorded detail (obscured by motion or noise)
Describe the method for objectively measuring resolution. Use a resolution test phantom - it has ll/mm (line pairs per millimeter) More visible line pairs, more spatial resolution OR FSS x OID / SOD
Describe the typical visual acuity of the human eye. The human eye is able to discern ~10 lp/mm
Describe the visible result of motion on an x-ray. Blurred image - appears as a blurred series of densities where no fine detail can be visualized.
What are the types of motion? A) voluntary B) involuntary C) equipment
How does a tech minimize the effects of motion? immobilization; suspended breathing; short exposure time (but increases mA); good communication with patient
What is the formula to calculate geometric unsharpness? P = FSS x OID / SOD
What are the digital image receptor factors that affect spatial resolution? DR is dependent on MATRIX SIZE/PIXEL SIZE; Matrix size - rows and columns forming square series of boxes give form to image; PIXEL size - individual box in matrix; PIXEL density - more pixels, smaller pixels, better spatial resolution
What are the units of measurement for spatial resolution? Spatial Frequency - measured in lp/mm - requires a minimum of 2 pixels; MTF - modulated transfer function - measures accuracy/quality of imaging system to reconstruct actual object on radiographic image System noise - loss of data within imaging system
What is a pixel? the basic unit of the display, each pixel represents one recorded detail, picture element
What is pixel size? how much info the pixel can store; the larger the pixel, the less information is recorded
What is matrix? array of cells, arranged in rows/columns stored in computer memory
What is matrix size? the total number of pixels within the recording device (flat panel detector or CR); increasing matrix size, decreases pixel size and improves spatial resolution
What is bit depth? the number of shades of gray that one pixel can record
What is MTF? Modulated Transfer Function-converting contrast values of different-sized objects (object contrast) into contrast intensity levels in image (image contrast). Capacity of IR to transfer modulation of input signal at given spatial frequency to its output.
What is system noise? irregularities within the imaging system that result in inaccurate/missing details in final image
When is deliberate motion used during exams? Motion blurring is used to remove superimposition and allow clearer imaging of a specific part through anatomy. Breathing technique is used to blur out ribs for T-spine and transthoracic humerus.
How does quantum mottle affect image clarity? Quantum mottle displays as tiny white spots on an image – it demonstrates too few photons reaching the IR. Because of this lack of information, there is less detail in final image (possibly concealing important pathology).
In what instances would a tech expect to see quantum noise? When insufficient mAs is being used (in conjunction with kVp) to image part correctly (enough photons); see in fluoro and if tech doesn't set correct technique for part/patient.
How do you remove quantum mottle/noise? by increasing mAs (remember to change kV)
Describe ACTUAL FOCAL SPOT. The actual area on the focal track that is impacted. It is detemined by the length of the filament and width of focusing cup depression.
Describe EFFECTIVE FOCAL SPOT. The area of the focal spot projected out of the tube in a downward path and toward the object being imaged. It is smaller than the ACTUAL focal spot.
What is the relationship of the actual focal spot to the effective focal spot? The effective focal spot is ALWAYS smaller than the actual focal spot due to the angle of the anode.
What is the Line Focus Principle? It states that by angling the anode target, a large focal spot can be maintained while a smaller effective focal spot is created to balance thermal heat and projected focal spot. Smaller focal spot sizes produce sharper images.
Define SID, OID and SOD. Explain the relationships between them. SID - source to image distance OID - object to image distance SOD - source to object distance OID+SOD=SID SID = OID + SOD
Define detail. The smallest separation of two lines or edges that can be recognized as separate structures on the image.
Define sharpness the accuracy of recorded detail
Created by: Larobbins