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Rad Technique
Chapter 17 and 18 Bushong viewing the digital image
| Question | Answer |
|---|---|
| WHAT IS SPATIAL RESOLUTION | In medical imaging, spatial resolution is a quantity of “spatial frequency” |
| WHAT LIMITS SPATIAL RESOLUTION | LIMITED TO PIXEL SIZE |
| HOW IS SPATIAL RESOLUTION MEASURED | LINE PAIR OF A GIVEN LENGTH (CM OR MM) |
| 3 ATTRIBUTES THAT DESCRIBE MODULATION TRANSFER FUNCTION (MTF) | Ability to render different sizes onto and image Objects with high spatial frequency, harder to image Objects considered HIGH contrast regardless of size |
| (MTF) WHAT IS A DRAW BACK OF HIGHER SPATIAL RESOLUTION? | LINE PAIRS BECOME MORE BLURRED |
| (MTF) A FUNCTION OF SPATIAL FREQUENCY | RATIO OF IMAGE TO OBJECT |
| WHAT IS THE PERCENTAGE OF AN IMAGING SYSTEMS SPATIAL RESOLUTION | SPATIAL FREQUENCY AT 10% MTF |
| WHAT OCCURS AT LOW SPATIAL FREQUENCIES | CONTRAST OF OBJECT IS PRESERVED |
| WHAT OCCURS AT HIGH SPATIAL FREQUENCIES | CONTRAST OF OBJECT IS LOST. |
| WHY DOES DIGITAL RADIOGRAPHY HAVE A HIGHER MTF AT LOW SPATIAL FREQUENCIES | BECAUSE OF WIDE DYNAMIC RANGE AND HIGH DQE |
| CONTRAST RESOLUTION IN DIGITAL RADIOGRAPHY RELATES TOO | SHADES OF GRAY AND DYNAMIC RANGE |
| DESCRIBE DYNAMIC RANGE | In digital, is identified by bit capacity of each pixel CT and MRI use 12 bit (4096) DR up to 14 bit (16,384 Mammography 16 bit (65,536) |
| WHAT IS ONE PRINCIPAL ADVANTAGE OF DIGITAL IMAGING | POST-PROCESSING |
| WHAT DOES WINDOW AND LEVEL DO? | ALLOWS US TO VIEW DYNAMIC RANGE ON POST-PROCESSING |
| WHAT IS SNR | SIGNAL TO NOSE RATIO Signal is portion of image forming x-rays that represent anatomy. Represents those x-rays transmitted and those absorbed photoelectrically |
| IN SNR NOISE DOES WHAT | LIMITS CONTRAST RESOLUTION |
| WHAT IS IDEAL SNR | HIGH SNR WHILE MAINTAING ALARA |
| HOW DO YOU INCREASE SNR | INCREASE mAs, WHICH ALSO INCREASE PATIENT DOSE |
| WHAT IS CONTRAST-DETAIL CURVE | Method used to evaluate spatial and contrast resolution |
| IN CONTRAST DETAIL CURVE IS CONTRAST IS HIGH THEN | SMALL OBJECT BE IMAGED |
| IN CONTRAST DETAIL CURVE IS CONTRAST IS LOW THEN | LARGE OBJECTS CAN BE IMAGED |
| IN CONTRAST DETAIL CURVE INCREASE IN mAs does what | SPATIAL RESOLUTION REMAINS THE SAME, BUT CONTRAST RESOLUTION IS IMPROVED AT HIGHER mAs. |
| IN CONTRAST DETAIL CURVE HIGHER mAs results in | LOWER CURVE, IT REPRESENTS BETTER CONTRAST BECAUSE TISSUE WITH LOWER CONTRAST CAN BE IMAGES. |
| WHAT IS SNR USED FOR | It is an instructive method of understanding how technique factors and imaging system factors influence spatial resolution and contrast resolution |
| WHAT IS THE OBJECT OF THE CONTRAST DETAIL CURVE | is to better understand that which influences spatial resolution—MTF—and that which influences contrast resolution |
| DOES IMAGE CONTRAST CHANGE WITH PATIENT DOSE | NO |
| CAN YOU OVEREXPOSE OR UNDEREXPOSE A DIGITAL IMAGE RECEPTOR | NEITHER |
| WHAT IS THE POTENTIAL LEVEL OF DECREASE OF PATIENT DOSE WITH DIGITAL IMAGING | Digital imaging should reduce patient dose by 20-50% depending on exam |
| WHAT IS PHOTOMETRY | Photometry is the science of the response of the human eye to light. |
| DESCRIBE PHOTOMETRIC QUANTITIES | IS A DESCRIPTION OF THE HUMAN VISUAL RESPONSE, AND WAS FIRST ATTEMPTED IN 1924 IT INCLUDED DEFINITION OF LIGHT INTENSITY, THE CANDLE, FOOT CANDLE AND CANDLE POWER |
| WHAT SHAPES ARE USED FOR PHOTOPIC'S OF BRIGHT LIGHT VISION | CONES |
| WHAT SHAPES ARE USED FOR SCOTOPIC DIM LIGHT VISION | RODS |
| WHAT IS THE BASIC PHOTOMETIC UNIT | LUMEN |
| WHAT DOES LUMINOUS FLUX DESCRIBE | the total intensity of light from a source |
| WHAT IS ILLUMINANCE | describes the intensity of light incident on a surface. |
| WHAT IS Luminance intensity | is a property of the source of light, such as a viewbox or a digital display device |
| WHAT IS Luminance | is a quantity that is similar to luminance intensity. |
| IN THE COSINE LAW, WHAT OCCURS WHEN A MONITOR IS VIEWED FROM AN ANGLE? | the contrast and the luminous intensity, as seen here, are reduced |
| WHAT IS AN ACTIVE MATRIX LIQUID CRYSTAL DISPLAY | A liquid crystal is a material state between that of a liquid and a solid. Active matrix liquid crystal displays are superior to cathode ray tube displays |
| IN THE AMLCD DESCRIBE THE PIXEL | Each pixel contains light-polarizing filters and films to control the intensity and color of light transmitted through the pixel. |
| WHY IS THE AMLCD AN INEFFICIENT DEVICE | Only approximately 10% of the backlight is transmitted through a monochrome monitor, and half of that through a color monitor. This inefficiency is due in part to light absorption in the filters and polarizers. |
| WHAT IS THE APERTURE RATIO OF AMLCD | Aperture ratios of 50% to 80% are characteristic of medical AMLCDs. |
| WHAT ARE THE ADVANTAGEOUS OF AMLCD | BETTER GRAY SCALE, NOT LIMITED BY VEILING GLARE, BETTER CONTRAST RESOLUTION, LESS NOISE |
| WHAT IS THE PRINCIPAL DISADVANTAGE OF AMLCD | is the angular dependence of viewing. |
| DESCRIBE PRE-PROCESSING | implements electronic calibration to reduce pixel-to-pixel, row-to-row, and column-to-column response differences |
| WHAT ARE OFFSET IMAGES AND GAIN IMAGES | are automatic calibration images designed to make the response of the image receptor uniform. Gain images are generated every few months, and offset images are generated many times each day. |
| WHAT IS FLAT FIELDING | corrects this defect and makes the image receptor response uniform. |
| HOW ARE PIXEL DEFECTS CORRECTED | signal interpolation |
| WHAT IS SIGNAL INTERPOLATION | IT IS USED TO CORRECT DEFECTIVE PIXELS The response of pixels surrounding the defective pixel is averaged, and that value is assigned to the defective pixel. |
| WHAT IS THE SOLUTION TO IMAGE LAG | OFFSET VOLTAGE BEFORE THE NEXT IMAGE IS REQUIRED |
| WHAT IS LINE NOISE | VOLTAGE VARIATIONS SEEN ALONG THE BUSES THAT DRIVE EACH PIXEL. |
| HOW DO YOU CORRECT LINE NOISE | apply a voltage correction from a row or a column of pixels in a dark, unirradiated area of the image receptor. |
| IN POST PROCESSING WHAT DOES SUBTRACT DO (DSA) | IMPROVES IMAGE CONTRAST |
| IN POST PROCESSING WHAT DOES PIXEL SHIFT DO | Reregister an image to correct for patient motion |
| WHAT IS SPATIAL FREQUENCY | A method of expressing object size. Measured in line pair per millimeter (lp/mm). |
| WHAT IS DETECTIVE QUANTUM EFFICIENCY | The ability of an image receptor to capture an x-ray. DQE is a function of the spatial frequency of the object. |
| WHAT IS CONTRAST RESOLUTION | The ability of an imaging system to render soft tissues on the image |
| WHAT IS MODULATION TRANSFER FUNCTION | The ratio of image contrast to object contrast as a function of the spatial frequency of the object. |
| WHAT IS K-SHELL BINDING ENERGY | The energy that holds a K-shell electron in its orbit around the nucleus. |
| WHAT ARE BAR PATTERN TEST TOOL | A test tool consisting of lead bars and equal inter-spaces of different sizes. Used to evaluate imaging system spatial resolution. |
| WHAT IS THE CONTRAST DETAIL CURVE | A graphical method of displaying the spatial resolution and contrast resolution of an imaging system. Used to compare various imaging systems and changes in their display |
| WHAT IS DYNAMIC RANGE | The gray scale. The number of shades of gray that can be rendered by an imaging system. |
| WHAT IS DMIST | Digital Mammography Imaging Screening Trial. |
| What tissues would be considered low spatial frequency structures? | Abdominal tissues, brain tissue |
| What tissues would be considered high spatial frequency structures? | Bone lung interface, skull brain interface, breast microcalcifications |
| What medical imaging system has the best spatial resolution? Why? | Screen film mammography. Small focal spot size. |
| What medical imaging system has the best contrast resolution? Why? | Magnetic resonance imaging. Proton density, T1 relaxation time, and T2 relaxation time values of tissue have far greater range than the x-ray attenuation coefficient. |
| What units are found along the vertical and horizontal axes of an MTF curve? | Vertical = modulation transfer function. Horizontal = spatial frequency. |
| What units are found along the vertical and horizontal axes of a contrast-detail curve? | Vertical = percent contrast. Horizontal = size. |
| How is image blur related to object spatial frequency? | Image blur increases as object spatial frequency increases. |
| What value of MTF is generally considered the limiting spatial resolution of an imaging system? | MTF = 0.1 or 10% MTF. |
| Why does a digital imaging system have a cutoff spatial frequency? | Digital imaging systems are limited by the size of the pixel. No imaging system can image an object smaller than 1 pixel. The cutoff spatial frequency is equal to the pixel size |
| Compare the dynamic range of the human visual system with those of screen-film radiography and digital imaging. | Humans can visualize approximately 30 shades of gray. Screen film is very wide, but we can’t visualize its range on a view box. Digital can be as high as 12 bits or 4096 shades of gray |
| A 12-bit dynamic range has how many shades of gray? | 4096 shades of gray |
| What were the principal findings of the DMIST, and what are their implications for medical imaging? | That digital mammography is equal to screen film mammography for all patients and is superior to screen film mammography for larger, denser breasts. |
| How does image integration in DSA improve signal-to-noise in the image? | Integrating signal is additive. Integrating noise is the square root of the number of integrations |
| Describe the quality control test tool designed to produce a contrast-detail curve | A pattern of various hole sizes with various hole depths. |
| Which—spatial resolution or contrast resolution—is more influenced by image noise? | Contrast resolution is worse as image noise increases. |
| Discuss “dose creep” and “technique creep.” | not adjusting exposures as frequently as with screen-film, by not changing factors between a lateral view and an AP view when these are taken consecutively. Technique creep should replace dose creep to effect reduced patient dose. |
| PACS | Picture Archiving and Communication System. |
| Lumen | The basic unit of photometry. Used to measure light intensity |
| Photometry | Photometry is the study of the response of the human eye to light |
| Scotopic | Dim light vision |
| Pixel shift | A postprocessing procedure to correct misregistration of images. |
| Interpolation | A mathematical method to estimate an unknown value lying between two known values |
| What is image registration, and how is it used? | When multiple images are used as in digital subtraction angiography, each must be able to faithfully overlie the other. |
| Describe the effect of off-axis viewing of a digital display system. | Reduced illumination and reduced image contrast. |
| What equipment is required to implement teleradiology? | Digital imaging systems and PACS. |
| What portion of medical imaging is now digital? | Perhaps as high as 70% and rising. |
| What photometric quantity best describes image brightness? | Candela. |
| How much digital capacity is required to store a 2000 × 2500 digital mammogram with a 16-bit grayscale? | 10 MB. |
| How is interpolation used to preprocess a digital image? | Electronic calibration to correct pixel to pixel, row to row, and column to column response differences. The processes of pixel to pixel interpolation, lag correction and noise correction are automatically applied with most systems. |
| What is the difference between bright vision and dim vision? | Bright vision is termed photopic vision and principally uses cones. Dim vision is termed scotopic vision and principally uses rods. |
| What is the approximate illumination of an office, major league night baseball, and a sunny snow scene? | Office = 100 fc, night baseball = 200 fc, snow scene = 10,000 fc. |
| How is DICOM used with medical images? | Digital Imaging and Communications in Medicine (DICOM) is a standardized imaging and interface protocol. |
| Briefly, how does an AMLCD work? | Back light is transmitted through liquid crystals with intensity determined by the voltage on the liquid crystal. |
| What is the difference between monochrome and polychrome? | Monochrome is black-and-white. Polychrome is full-color. |
| What are some advantages of digital display devices over a digital cathode ray tube? | No veiling glare, flat face, square pixel, and uniformity of intensity. |
| What is the aperture ratio of a medical AMLCD? | That portion of a pixel available to transmit light. |
| What ergonomic properties are incorporated into a digital image workstation? | Low ambient light level, comfortable seating/standing, proper monitor level and distance. |
| What are four major photometric quantities? | Luminous flux, illuminance, luminance intensity, and luminance. |
Created by:
MARCOZING
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