Recorded Detail Laura Herz BA RTR Radiographic Quality

Recorded Detail Laura Herz, BA, RT(R) Radiographic Quality

Recorded Detail �Definition: degree of geometric sharpness or accuracy of the structural lines actually recorded in the image One of two geometric properties of radiographic image quality Also known as: ▪ ▪ Definition Sharpness Resolution Detail

Recorded Detail �Poor resolution on the radiographic image is seen as a lack of sharp definition Penumbra: geometric unsharpness around the periphery of an image �All radiographic images have less recorded detail than the actual object being imaged Radiographer’s Goal: to control the degree of unsharpness or penumbra so it does not interfere with image diagnosis

Unit of Recorded Detail �Primary unit of resolution: line pairs per millimeter (lp/mm) Human visual acuity: 5 lp/mm

Assessing Recorded Detail �Simple Evaluation: Trabeculae of bone is an excellent guidepost to image resolution Absence of blur/motion �Mathematical Evaluation: Line Spread Function (LSF): complex mathematical measurement of the boundaries of an image Modulation Transfer Function (MTF): mathematical assessment of the performance of an imaging system ▪ MTF = information recorded ÷ information available

Factors Affecting Recorded Detail �Motion �Materials �Geometry

Motion �Motion fails to permit enough time for a well- defined image to form Voluntary ▪ Under direct control of patient Involuntary ▪ Not under direct control of patient; heartbeat, peristalsis, tremors, babies Equipment

Motion �Voluntary motion controlled by: Communication ▪ Instructions should be clear, concise, and understandable Immobilization/comfort devices ▪ Foam pads, angle sponges, blankets, sand bags, tape compression, commercial immobilizers, human immobilizers Reduction in exposure time

Motion �Involuntary motion controlled by: Reduction in exposure time

Reducing Exposure Time • Shortens length of exposure to compensate for involuntary and/or voluntary motion Suggested Order for Reducing Exposure Time CHANGE EFFECT 1. Increase m. A Decrease Time 2. Increase Screen Speed Decrease Time 3. Decrease SID Decrease Time 4. Increase k. Vp Decrease Time

Increase m. A to Reduce Exposure Time �Density can be maintained with an increase in m. A and a proportional decrease in time Each exposure will then use the same m. As = m. A x time ▪ 100 m. As = 100 m. A x 1 sec ▪ 100 m. As = 400 m. A x. 25 sec m. As m. A X time

Increase Screen Speed to Reduce Exposure Time �Each screen speed produces a different density on the radiograph Greater the screen speed, the greater the density Greater screen speed requires a decrease in m. As to maintain density decrease in m. As indirectly causes a decrease in exposure time Old screen speed New screen speed = New m. As Old m. As

Increase Screen Speed to Reduce Exposure Time �You take a radiograph utilizing 40 m. As and a 200 screen speed. In order to produce the same density with a 400 screen speed, what would your m. As need to be?

Decrease SID to Reduce Exposure Time �Inverse Square Law Intensity of radiation is inversely proportional to the square of the distance from the source of radiation Intensity 1 Intensity 2 = Distance 2² Distance 1² There is an inverse relationship between the SID and the radiation intensity at the film

Decrease SID to Reduce Exposure Time �To maintain density, if the SID decreases, the m. As must be decreased decrease in m. As indirectly causes a decrease in exposure time Density Maintenance Formula Old m. As New m. As = Old distance² New distance²

Decrease SID to Reduce Exposure Time �You take a radiograph utilizing 400 m. A at. 05 seconds at a 72” SID. A new radiograph is taken at a 36” SID. What would the new m. As need to be to maintain density? �What would be the new time?

Increase k. Vp to Reduce Exposure Time �Kilovoltage (k. Vp) is the controlling factor for radiographic contrast Determines the quality or penetrating power of the beam �There is a direct relationship between k. Vp and density

Increase k. Vp to Reduce Exposure Time �To maintain density, if the k. Vp decreases, the m. As should increase �To maintain density, if the k. Vp increases, the m. As should decrease in m. As indirectly causes a decrease in exposure time 15% Rule for maintaining density: ▪ If the k. Vp is changed by 15%, the m. As should be changed by a factor of 2 ▪ If k. Vp is decreased by 15%, m. As should be doubled ▪ If k. Vp is increased by 15%, m. As should be cut in half

Increase k. Vp to Reduce Exposure Time �You take a radiograph utilizing 100 m. A at 1 second with 70 k. Vp. You increase your k. Vp to 80. What is your new m. As? �What would be the new time? �You further increase your k. Vp to 92. What is your new m. As? �What would be the new time?

Materials �Film �Intensifying Screens �Poor Film-Screen Contact

Materials �Film Always some loss of detail with the use of film, however, all films employed in radiography are capable of resolving far greater lp/mm than the human eye is capable of visualizing

Materials �Intensifying Screens Phosphor size and phosphor layer have an influence on recorded detail ▪ As phosphor size and layer thickness increase, screen speed increases ▪ As phosphor size and layer thickness increase, recorded detail decreases

Materials � Intensifying Screens Quantum Mottle: grainy or blotchy appearance caused by insufficient photons (insufficient m. As) striking the image receptor; refers to the fact that the image is intensified (converted to light and made brighter) rather than produced only by x-ray photons ▪ Often noticed with increasing screen speeds or increasing k. Vp

Materials �Poor Film-Screen Contact Increased distance between the intensifying screen phosphors and the film ▪ Amplifies existing unsharpness and reduces recorded detail Calculating the effect on recorded detail: Old Unsharpness X Poor Film-Screen Contact²

Geometry �Focal Spot Size �SID �OID

Geometry �Focal Spot Area on the anode of the x-ray tube that is hit with electrons from the filament All x-ray photons in the beam originate from this point

Geometry

Geometry �If the focal spot is smaller, the image will be less spread out and will appear sharper on the radiograph �If the focal spot is smaller, the greater the heat applied to that point on the anode, which results in limitations when selecting the focal spot size Tube Rating Charts Anode Cooling Charts

Geometry �SID Recorded detail is increased/improved when the source to image receptor distance (SID) is increased

Geometry �OID Recorded detail is increased/improved when the object to image receptor distance (OID) is decreased Calculating Geometric Unsharpness: Focal Spot Size x OID SOD