Digital Imaging Review RT 255 1 Display Workstations

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Digital Imaging Review RT 255 1

Digital Imaging Review RT 255 1

Display Workstations • Conventional film/screen radiography uses large multiviewer lightboxes. • With early PACS,

Display Workstations • Conventional film/screen radiography uses large multiviewer lightboxes. • With early PACS, radiologists thought that they needed 4 -6 monitors. • Now, the number of monitors has dropped to an average of 2. • Development of viewing software and better hardware. 2

 • The CRT is the most popular monitor on the market. • It

• The CRT is the most popular monitor on the market. • It consists of a cathode and anode within a vacuum tube. • Cathode boils off a cloud of electrons, and then a potential difference is placed on the tube. • A stream of electrons is sent across to the anode, which in the case of the monitor is a sheet of glass coated with a phosphor layer. CRT 3

MONITORS: Display Workstations • Early PACS reading rooms required supplemental air-conditioning to offset the

MONITORS: Display Workstations • Early PACS reading rooms required supplemental air-conditioning to offset the heat from multiple CRTs. • Resolution and orientation of the monitor is also a factor in determining which type of monitor is to be used. • Most cross-sectional imaging is read on a 1 K square monitor. • Most computed radiography (CR) and digital radiography (DR) images are read on at least a 2 K portrait monitor 4

LCD • 1. 3 megapixels • to 5 megapixels. • mammography imaging = •

LCD • 1. 3 megapixels • to 5 megapixels. • mammography imaging = • at least 5 megapixel resolution is required. 5

 • Rads VIEWER • 4 K or higher 6

• Rads VIEWER • 4 K or higher 6

Physician Review Stations Monitors • Step-down model of the radiologist’s reading station (lower res)

Physician Review Stations Monitors • Step-down model of the radiologist’s reading station (lower res) • Some functions reduced • One of the most important features • is ability to view current and previous reports with images. • Many vendors are integrating • the RIS functions • with PACS software. 7

Technologist QC Stations • review images after acquisition but before sending them to the

Technologist QC Stations • review images after acquisition but before sending them to the radiologist • May be used to improve or adjust image-quality characteristics • May be used to verify patient demographic information • Placed between the CR and DR acquisition modalities as a passthrough to ensure that the images have met the departmental quality standard 8

Technologist QC Station • Generally has a 1 K monitor • Does not have

Technologist QC Station • Generally has a 1 K monitor • Does not have the resolution capabilities of the radiologist’s reading station • Care required of technologist when manipulating images not to change the appearance too much from original acquired image 9

Technologist workstation monitors are used in brightly lighted areas. So monitor luminance, the brightness

Technologist workstation monitors are used in brightly lighted areas. So monitor luminance, the brightness of a monitor display, is an important consideration. Also, the monitor must allow a technologist to visualize enough detail to discern motion and that the recorded lines are sharp and visible. 10

The File Room Workstation • • • Workstation may be used to look up

The File Room Workstation • • • Workstation may be used to look up exams for a physician or to print copies of images for the patient to take to an outside physician. Many hospitals are moving away from printing films because of the cost. • Hospitals are moving toward burning compact disks (CDs) with the patient’s images. 11

Name the 3 types of monitors • Two major types of monitors with a

Name the 3 types of monitors • Two major types of monitors with a third type gaining acceptance: • CRT • LCD • Plasma screen 12

ARRT DEFINITIONS Image Display= MONITORS • viewing conditions – (i. e. , luminance, ambient

ARRT DEFINITIONS Image Display= MONITORS • viewing conditions – (i. e. , luminance, ambient lighting) • • spatial resolution contrast resolution/dynamic range DICOM gray scale function window level and width function 13

viewing conditions luminance, ambient lighting • How does this affect viewing images? • Surrounding

viewing conditions luminance, ambient lighting • How does this affect viewing images? • Surrounding light impacted what was seen on image – now : With different monitors: • LCD gives more light. • LCD can be used in areas with a high amount of ambient light. “dark rooms” not necessary 14

WINDOW LEVEL / WIDTH Which one controls Denisty (brightness) ? Contrast What else control

WINDOW LEVEL / WIDTH Which one controls Denisty (brightness) ? Contrast What else control these in DIGITAL IMAGING? 15

 • • The ability to window is a valuable feature of all digital

• • The ability to window is a valuable feature of all digital images. Windowing is the process of selecting some segment of the total pixel value range (the wide dynamic range of the receptors) and then displaying the pixel values within that segment over the full brightness (shades of gray) range from white to black. Important point. . . Contrast will be visible only for the pixel values that are within the selected window. All pixel values that are either below or above the window will be all white or all black and display no contrast. The person controlling the display can adjust both the center and the width of the window. The combination of these two parameters determine the range of pixel values that will be displayed with contrast in the image. 16

Enhanced Visualization Image Processing • • Takes image diagnostic quality to a new level

Enhanced Visualization Image Processing • • Takes image diagnostic quality to a new level Increases latitude while preserving contrast Process decreases windowing and leveling Virtually eliminates detail loss in dense tissues 17

Nyquist frequency Review • The highest spatial frequency that can be recorded by a

Nyquist frequency Review • The highest spatial frequency that can be recorded by a digital detector. • is determined by the ________ • The Nyquist frequency is half the number of pixels/mm. 18

10 PIXEL DENSITY WHAT IS THE NYQUIST FREQUENCY= ? 19

10 PIXEL DENSITY WHAT IS THE NYQUIST FREQUENCY= ? 19

A digital system with a pixel density of 10 pixels/mm would have a Nyquist

A digital system with a pixel density of 10 pixels/mm would have a Nyquist frequency of 5 line pair/mm. 10 PIXEL DENSITY WHAT IS THE NYQUIST FREQUENCY= ? 20

Sampling Frequency ? Define …… 21

Sampling Frequency ? Define …… 21

Sampling Frequency • The sampling frequency is the rate at • which the laser

Sampling Frequency • The sampling frequency is the rate at • which the laser extracts the image data • from the plate. • What other term does this relate to? 22

Nyquist Frequency • The Nyquist Frequency will be ½ of the sampling frequency. •

Nyquist Frequency • The Nyquist Frequency will be ½ of the sampling frequency. • A plate that is scanned using a sampling frequency of 10 pixels per millimeter would not be able to demonstrate more than 5 line pairs per millimeter based upon the Nyquist Frequency. • The Nyquist Frequency allows the • determination of the spatial resolution for • a given sampling frequency. 23

LUT • In the typical digital radiographic system, a variety of LUTs are installed.

LUT • In the typical digital radiographic system, a variety of LUTs are installed. • The appropriate LUT is then automatically selected to give the desired contrast characteristics to match the type of procedure (chest, extremity, etc) that is designated by the operator. a histogram of the luminance values derived during image acquisition used as a reference to evaluate the raw information and correct the luminance values. a mapping function in which all pixels are changed to a new gray value. 24

LOOK UP TABLE (LUT) Linear LUT Black Saturation White Saturation Black Shirt Facial Tones

LOOK UP TABLE (LUT) Linear LUT Black Saturation White Saturation Black Shirt Facial Tones * No Detail in Black Areas * High Contrast * Only Detail in White Areas can be seen * No Detail in White Areas * Low Contrast * Only Detail in Black Areas can be seen 25

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ARRT definitions Image Receptors digital image characteristics – spatial resolution – sampling frequency –

ARRT definitions Image Receptors digital image characteristics – spatial resolution – sampling frequency – DEL (detector element size) – receptor size and matrix size – image signal (exposure related) – quantum mottle – SNR (signal to noise ratio) or – CNR (contrast to noise ratio) 27

image signal (exposure related) Exposure Indicators • The amount of light given off by

image signal (exposure related) Exposure Indicators • The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received. • The light is converted into a signal that is used to calculate the exposure indicator number, which is a different number from one vendor to another. 28

Digital artifacts • Grid Lines: Appear as grid cutoff. • Moire (Aliasing) – wavy

Digital artifacts • Grid Lines: Appear as grid cutoff. • Moire (Aliasing) – wavy artifact occurs because the grid lines and the scanning laser are parallel. – When the spatial frequency is greater than the Nyquist frequency • Maintenance (e. g. , detector fog): When errors occur in equipment performance, corrective action must occur. These corrections will generally be done by service personnel employed by the vendor. • non-uniformity, erasure - blub problems 29

How else can Morie OCCUR? 30

How else can Morie OCCUR? 30

ARRT definitions quantum mottle failure of an imaging system to record densities usually caused

ARRT definitions quantum mottle failure of an imaging system to record densities usually caused by a lack of xray photons. “PHOTON STARVED” KVP & MAS HOW IS THIS AFFECTED IN DR / CR? 31

PREPROCESSING ARTIFACTS - dead detector elements dead columns or rows nonuniform response heel effect

PREPROCESSING ARTIFACTS - dead detector elements dead columns or rows nonuniform response heel effect (fixed systems) light guide variations ghosting 32

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ARRT definitions Image Receptors digital image characteristics – spatial resolution – sampling frequency –

ARRT definitions Image Receptors digital image characteristics – spatial resolution – sampling frequency – DEL (detector element size) – receptor size and matrix size – image signal (exposure related) – quantum mottle – SNR (signal to noise ratio) or – CNR (contrast to noise ratio) 35

Image Acquisition and Readout • PSP (photo-stimulable phosphor) • flat panel detectors – (direct

Image Acquisition and Readout • PSP (photo-stimulable phosphor) • flat panel detectors – (direct and indirect) 36

CR Imaging Plate • Construction • Image recorded on a thin sheet of plastic

CR Imaging Plate • Construction • Image recorded on a thin sheet of plastic known as the imaging plate - PSP • Consists of several layers: • Phosphor? 37

Imaging Plate • Phosphor? • BARIUM FLUORO • HALIDE WITH • A EUROPIUM BASE

Imaging Plate • Phosphor? • BARIUM FLUORO • HALIDE WITH • A EUROPIUM BASE 38

Digital Radiography • Two types of digital radiography • Indirect capture DR • Machine

Digital Radiography • Two types of digital radiography • Indirect capture DR • Machine absorbs x-rays and converts them to light. • CCD or thin-film transistor (TFT) converts light to electric signals. • Computer processes electric signals. • Images are viewed on computer monitor. 39

Digital Radiography • Direct capture DR • Photoconductor absorbs x-rays. • TFT collects signal.

Digital Radiography • Direct capture DR • Photoconductor absorbs x-rays. • TFT collects signal. • Electrical signal is sent to computer for processing. • Image is viewed on computer screen. 40

Image Acquisition and Readout flat panel detectors Phosphors? – direct = Am SELENIUM –

Image Acquisition and Readout flat panel detectors Phosphors? – direct = Am SELENIUM – indirect = Am SILICON 41

 • CR PSL light guide PMT/PD • Indirect Cs. I/GOS contact layer PD/TFT

• CR PSL light guide PMT/PD • Indirect Cs. I/GOS contact layer PD/TFT array • Direct a-Se none TFT array • CCD/CMOS Cs/GOS lens/fiber CCD/CMOS 42

CMOS ? 43

CMOS ? 43

CMOS ? • Complimentary metal-oxide semiconductor (CMOS) – A photographic detector. 44

CMOS ? • Complimentary metal-oxide semiconductor (CMOS) – A photographic detector. 44

 • CCD and CMOS systems – both use a scintillator. These systems are

• CCD and CMOS systems – both use a scintillator. These systems are cameralike, • they both use lenses to focus the light onto a detector. 45

 • • Digital Systems electronic collimation grayscale rendition or look-up table (LUT) edge

• • Digital Systems electronic collimation grayscale rendition or look-up table (LUT) edge enhancement/ – noise suppression • contrast enhancement • system malfunctions (e. g. , ghost image, banding, erasure, dead pixels, readout problems, printer distortion) 46

Image Data Recognition and Preprocessing shutter • Agfa uses the term collimation, Kodak uses

Image Data Recognition and Preprocessing shutter • Agfa uses the term collimation, Kodak uses the term segmentation, and Fuji uses the phrase “exposure data recognition. ” • All systems use a region of interest to define the area where the part to be examined is recognized and the exposure outside the region of interest is subtracted. 47

 • So in essence, rescaling provided an acceptable image, despite an excess level

• So in essence, rescaling provided an acceptable image, despite an excess level of exposure to the receptor. What about the dose to the patient? • Excessive exposure to receptor without rescaling. • Excessive exposure to receptor with rescaling. 48

Rescaling • image pixel values to appear appropriate, display properly, can lead to overexposing

Rescaling • image pixel values to appear appropriate, display properly, can lead to overexposing a patient. • The visual cue to the technologist that overexposure has occurred isn’t present. • With an analog system, a technologist would have seen the image on the left as it came out of the processor and used the excessive density of the image as a visual cue to repeat the image. • Rescaling forces a technologist to look elsewhere for signs that a proper exposure was used to produce an image. 49

Dose creep • refers to the potential to gradually increase patient exposure over time.

Dose creep • refers to the potential to gradually increase patient exposure over time. • However, a technologist lacks visual feedback that additional radiation is being used to produce the images 50

DAP • The dose area product (DAP) meter is a device that may be

DAP • The dose area product (DAP) meter is a device that may be interlinked with the x-ray unit to determine the actual patient entrance skin exposure dose with accurately calibrated equipment. Currently, no standards are established for using a dose area product meter These two radiographs show the difference in entrance skin exposure measured by the DAP meter. The area with a smaller exposure field size carries a lower exposure without reducing image quality 51

Exposure Latitude • The analog receptor exposure latitude ranges from approximately • 30% underexposed

Exposure Latitude • The analog receptor exposure latitude ranges from approximately • 30% underexposed • to 50% overexposed relative to • the “ideal” exposure level. 52

Exposure Latitude The digital image receptor • exposure latitude ranges from • approximately •

Exposure Latitude The digital image receptor • exposure latitude ranges from • approximately • 50% underexposed • to 100% over exposure • relative to the “ideal” exposure level. 53

Note It is important to note that just because a • digital imaging system

Note It is important to note that just because a • digital imaging system has the capacity to • produce an image from gross underexposure • or gross overexposure it does not equate to • greater exposure latitude. • The reason the system is capable of producing an image when significant exposure errors occur is through a process called automatic rescaling. 54

 • In a digital system, underexposure of • 50% or greater will result

• In a digital system, underexposure of • 50% or greater will result in a mottled • image. • �� In a digital system, overexposure • greater than 200% of the ideal will result • in loss of image contrast. 55

Image Evaluation: Brightness and Contrast in Images • • Exposure Field Recognition Error Gross

Image Evaluation: Brightness and Contrast in Images • • Exposure Field Recognition Error Gross Overexposure Excessive Scatter Striking the Receptor Excessive Fog on the Receptor Grid Cutoff Intra-Field or Off-Focus Radiation Wrong Menu Selection 56

EDR • Exposure Data Recognition • When laser scans it is looking for area

EDR • Exposure Data Recognition • When laser scans it is looking for area of plate that has exposure • Some read from center out and look for two sides of collimation • Works best when image centered 57

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S# 8, 357 S# 12, 361 lat CXR 60

S# 8, 357 S# 12, 361 lat CXR 60

Exposure Numbers • The exposure numbers can only be used if all other parameters

Exposure Numbers • The exposure numbers can only be used if all other parameters are correct – Centering to plate – Collimation • Position over AEC, look at m. As readout to determine if poor positioning caused light or dark image 61

Same technique, different centering and collimation S# 592 S# 664 62

Same technique, different centering and collimation S# 592 S# 664 62

ARRT SPECS - DIGITAL • PACS • HIS (hospital information system) - work list

ARRT SPECS - DIGITAL • PACS • HIS (hospital information system) - work list • RIS (radiology information system) • DICOM • Workflow (inappropriate documentation, lost images, mismatched images, corrupt data) 63

PACS • Image is stored on a computer: retrieval and viewing system for digital

PACS • Image is stored on a computer: retrieval and viewing system for digital imaging examinations. • The PACS software provides “tools” that enable a PACS operator to manipulate images. • The basic image manipulations possible are: magnification and minification of an image; altering image brightness and contrast; and annotating the image using text, symbols, lines and arrows. 64

Picture Archival and Communication Systems • Networked group of computers, servers, and archives to

Picture Archival and Communication Systems • Networked group of computers, servers, and archives to store digital images • Can accept any image that is in DICOM format • Serves as the file room, reading room, duplicator, and courier • Provides image access to multiple users at the same time, ondemand images, electronic annotations of images, and specialty image processing 65

HIS – RIS INTERFACE 66

HIS – RIS INTERFACE 66

RIS Data Storage • Less ERRORS • A radiology information system, or RIS, is

RIS Data Storage • Less ERRORS • A radiology information system, or RIS, is a data system for patient-related functions in the radiology department. Examples of functionality a RIS provides within a radiology department include (but are not limited to): • scheduling • appointments; • collecting and displaying orders for radiologic examinations; • storing and displaying patient data; • tracking patients • providing patient and order data to a PACS; storing and distributing radiology reports; providing billing services; and providing a database to track and project trends. 67

HIS • A hospital information system, or HIS, is a paper and/or data system

HIS • A hospital information system, or HIS, is a paper and/or data system that manages the administrative, financial and clinical information necessary to operate a hospital or health care system 68

Health Level 7 (HL 7) • HL 7 are the software standards established for

Health Level 7 (HL 7) • HL 7 are the software standards established for exchanging electronic information in health care. PACS is mainly concerned with images and data associated with images, whereas HL 7 sets standards for transmitting text-based information throughout a medical center. 69

Cassette-based systems PSP plates • Turbid phosphors ? • Structured phosphors ? 70

Cassette-based systems PSP plates • Turbid phosphors ? • Structured phosphors ? 70

 • Turbid Phosphor – A phosphor layer with a random distribution of phosphor

• Turbid Phosphor – A phosphor layer with a random distribution of phosphor crystals within the active layer. • Structured (needle) phosphor – A phosphor layer with columnar phosphor crystals within the active layer. Resembles needles lined up on end and packed together. 71

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Exposure index • Cassette based– represents exposure level to plate • a. Vendor specific

Exposure index • Cassette based– represents exposure level to plate • a. Vendor specific values • 1). Sensitivity “S” (Fuji, Philips, Konica) inversely related to exposure- 200 S# =1 m. R to the plate – optimal range 250 -300 for trunk, 75 -125 for extremities • 2). Exposure Index (EI)- (Kodak) – directly related to exposure has a logarithmic component (change of 300 in EI = factor of 2; i. e. 1800 is exposed twice as much as 1500) optimal range 1800 -1900. • 3). Log Mean (Lg. M) - (Agfa) – directly related to exposure has a logarithmic component (change of 0. 3 in Lg. M = factor of 2, ie 2. 3 is exposed twice as much as 2. 0) optimal range 1. 9 -2. 1. 73

 • MTF ? 74

• MTF ? 74

MODULATION TRANSFER FUNCTION - MTF • A measure of the ability of the imaging

MODULATION TRANSFER FUNCTION - MTF • A measure of the ability of the imaging system to preserve signal contrast as a function of the spatial resolution. • Every image can be described in terms of the amount of energy for each of its spatial frequency components. • MTF often is regarded as the ideal expression of the image quality provided by a detector. 75

Exposure myths associated with digital systems 1. m. As – myth: digital is m.

Exposure myths associated with digital systems 1. m. As – myth: digital is m. As driven. Truth: digital is exposure driven. The digital detector is unable to discriminate whether the exposure change was m. As or k. Vp. The only thing that matters is exposure to pixels. 2. k. Vp – myth: digital is k. Vp driven. Truth: see above 3. Collimation – myth: you cannot collimate. Truth: you can and should collimate. Inappropriate collimation will cause a histogram analysis error. 76

Exposure myths associated with digital systems 4. Grid – myth: cannot use grids and

Exposure myths associated with digital systems 4. Grid – myth: cannot use grids and don’t need them. Truth: digital systems are sensitive to scatter just like film; in fact they are more sensitive. Appropriate grid useis even more important. A grid should be used when the remnant beam is more than 50% scatter, chest larger than 24 cm and anything else larger than 12 cm. 5. SID – myth: magnification doesn’t occur with digital so SID is unimportant. Truth: Geometric rules of recorded detail and distortion are unchanged from film to digital. 77

Exposure myths associated with digital systems 7. Fog – myth: digital systems can’t be

Exposure myths associated with digital systems 7. Fog – myth: digital systems can’t be fogged by scatter or background radiation. Truth: digital systems are more sensitive to both. 8. Myth: fluorescent lights fog PSP plates. Truth: that is not true. 78

Next • ODIA - Summer Review • Prep for Registry Exam! 79

Next • ODIA - Summer Review • Prep for Registry Exam! 79