A Comprehensive Review of

Image Production
Presented by:
John Fleming, M.Ed., RT(R)(MR)(CT)
St. Petersburg College
Office: (727) 341-3758
E-mail: flemingj@spcollege.edu
 Lesson Objectives:
 ARRT Content Specifications
 Image Production
Image Acquisition & Technical Evaluation
Equipment Operation & Quality Assurance
 Midterm & Final Exam
 https://www.arrt.org/Handbooks

2017
January-December 2017
ARRT Content Specifications:

Content Category Questions

A. Patient Care 33
B. Safety 53
C. Image Production 50
D. Procedures 64
Total 200
D. Digital Imaging Characteristics
1. spatial resolution (equipment related)
a. pixel characteristics (e.g. size, pitch)
b. detector element (DEL) (e.g. size,
pitch, fill factor)
c. matrix size
d. sampling frequency
2. contrast resolution (equipment related)
a. bit depth
b. modulation transfer function
c. Detective quantum efficiency (DQE)
 ARRT Standard Definitions:
Attachment C
Term Definition
Spatial Resolution The sharpness of the structural
edges recorded in the image.
Receptor Exposure The amount of radiation striking
the image receptor.
Dynamic Range The range of exposures that may
be captured by a detector.
 References:
Radiography in the Digital Age by Carroll
Digital Radiography an Introduction by Seeram
Radiographic Imaging & Exposure by Fauber
Brightness & Contrast in Digital Imaging by
Cummings (Corectec)
The Physical Principles of Medical Imaging by
Sprawls
Part I: An Overview of Digital
Radiography
 Digital Radiography:
 Term that includes both computed radiography
(CR) and direct radiography (DR).
 Digital radiography entered the medical field in
the 1970s with the advent of computed
tomography (CT) & digital subtraction
angiography (DSA).
 Computed
Radiography
 Computed Radiography (CR):
 Cassette-based digital radiography.
 Fuji introduced the first CR systems in the US
in 1983.
 Did not take off until the 1990s.
 Computed Radiography (CR):
 CR is a marketing term for photostimulable
phosphor (PSP) detector systems.
An analog signal (data) is created and
interpreted by analog and digital devices.
 As the exit beam strikes these phosphors,
some light is emitted but most of the energy is
trapped in the PSP screen.
PSP screens are sometimes called storage
phosphors or imaging plates.
 CR Imaging Plates:
 They are made of barium fluorohalide
crystals.
85% BaFBr and 15% BaFI.
 CR Imaging Plates:
 CR imaging plates are activated by a small
quantity of europium.
Europium doping creates defects in the
barium fluorohalide crystals.
Following exposure to the exit beam, these
defects provide an efficient means to trap
electrons at a different energy level.
CR Imaging Plate & Cassette:
CR Reader:
CR Reader:
Scanning the Imaging Plate:
 CR Processing:
 Following exposure to the exit beam, a latent
image is formed on the CR plate.
 The cassette is placed in a CR reader and the
plate is removed.
 It is then scanned by a high-intensity laser
beam (red light).
 The laser stimulates the movement of some of
the trapped electrons back to their original
position.
 CR Processing:
 As this occurs, there is an emission of a blue-
green light from the CR plate.
This process is called light-stimulated
phosphorescence.
 The blue-green light is collected by a fiber
optic light guide and sent to a PMT where an
electronic signal is generated.
The red laser light is filtered out and
removed.
 CR Processing:
 Analog-to-digital Converter (ADC)
Converts the electric signal from the PMT
into a digital signal.
 Workstation
Allows for post processing image
manipulation.
Final images are sent to PACS.
 Clearing the CR Plate:
 Exposure to the laser beam will not “reset” all
of the electrons within the CR plate back to
their original position.
 It must be exposed to a bright white light to
remove any residual energy prior to returning
to the cassette.
If this does not occur, a ghost image will
remain on the CR plate.
Ghost Image:
Ghost Image:
 CR Sensitivity to Noise:
 Imaging plates are very sensitive to
background and scatter radiation.
 They should be erased after 48 hours of
nonuse.
CR vs. Background Radiation:

Erased Cassette
CR vs. Background Radiation:

One Week
CR vs. Scatter Radiation:
CR Collimation Considerations:
 If the collimated borders are not recognized,
the image data analysis will include all of the
data outside the collimation.
 The final image may not have the correct level
of brightness and contrast.
 Tightly collimated images should be placed in
the center of the IR.
Exposure Indicators vs. mAs (x):
Symbol ½(x) Perfect (x) 2(x)

Fuji/Konica Minolta/
S# 400 200 100
Siemans/Philips

GE/Agfa lgM 1.9 2.2 2.5

Kodak/Carestream EI 1700 2000 2300

This is our goal…ALARA.

 mAs vs. Konica Minolta S#:
60 kVp @ 2 mAs 60 kVp @ 4 mAs 60 kVp @ 8 mAs

S# 397 S# 201 S# 98
Which of these images would be most ideal?
Direct Radiography
Unit
 Direct Radiography (DR):
 DR employs a flat panel image receptor (IR)
that is about the size of a CR cassette.
 Two Types of Flat Panel IRs:
Indirect Capture
Direct Capture
Flat Panel IR:
Flat Panel IR:
Indirect Capture Flat Panel IR:
Image Forming Beam
Surface Reflector
Scintillation Detector Array that
contains CsI or GOS

Light Photon Production

Optical Clad Photodiodes that

contains Amorphous Silicon (a-Si)
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
AD Converter
Flat Panel Detector that contains Converts Electronic
a Capacitor & a Thin-Film Signal into a Digital
Transistor Signal Workstation
 Indirect Capture Flat Panel IR:
 Surface Reflector
Directs divergent light back towards
photodiode.
This will result in a decrease in patient dose
and an increase in noise.
 Indirect Capture Flat Panel IR:
 Scintillation Detection Array
Contains columns of fluorescent materials
that convert x-rays into light.
Made of cesium iodide (CsI) or Gadolinium
Oxysulfide (GOS).
 CsI produces slightly higher resolution

images but it is more expensive ($5K)

and requires a higher dose than GOS.
Both result is a less dose than direct capture
because the light intensifies the image.
 Indirect Capture Flat Panel IR:
 Optical Clad Photodiode
Converts light into electrons.
Made of amorphous silicon (a-Si).
 Indirect Capture Flat Panel IR:
 Flat Panel Detector
3000 x 3000 matrix that contains 9 million
individual square detector elements (DEL)
within a glass substrate.
Each DEL contains a capacitor and either a
thin-film transistor (silicon TFT) or a field-
efficient transistor (FET).
The capacitor collects electrons until the read-
out electronics are activated.
The TFT/FET allows for the signal discharged
from the capacitor to reach the ADC.
 Indirect Capture Flat Panel IR:
 Analog-to-digital Converter (ADC)
Converts the electric signal from the flat
panel detector into a digital signal.
 Workstation
Performs basically the same functions as
for CR.
 A DR room can cost $150,000.
 The flat panel detector can cost $50,000 and is
highly proprietary.
Direct Capture Flat Panel IR:
Image Forming Beam

X-ray Photoconductor Layer made of

Amorphous Selenium (a-Se)
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
e- e- e- e- e- e- e- e- e-
AD Converter

Flat Panel Detector that contains Converts Electronic

a Capacitor & a Thin-Film Signal into a Digital Workstation
Transistor Signal
 Direct Capture Flat Panel IR:
 No light emission is involved.
 Results in less quantum noise and improved image
quality but higher patient dose.
 Often used in Mammography.
 X-ray Photoconductor Layer
Made of amorphous selenium (a-Se).
Prior to exposure, a voltage is applied.
X-ray interaction causes ionizations to occur that
are sent to the flat panel detector.
Images are then produced in the same manner as
indirect capture flat panel IRs.
Digital Radiography
Processing Unit
Digital Radiography Processing:
 Digital radiography employs the use of
histogram and look-up-table (LUT)
algorithms to manipulate image brightness
and contrast.
Histograms: Luminance Values
 A visual representation of raw pixel values.

Digital Frequency

0 Digital Value 2048

Raw Data
Raw Image
Histograms: Luminance Values
Bone Area
Direct Exposure Area

Digital Frequency
Bone Area

Soft Tissue
Area

0 Digital Value 2048

Soft Tissue Area Direct Exposure Area

 Histograms: Image Rescaling
Digital Frequency

Raw Data

0 Digital Value 2048

The acquired histogram containing the VOI is compared to a
default histogram & a rescaled image is produced.
 Histograms: Image Rescaling
Default Histogram
Digital Frequency

Raw Data

0 Digital Value 2048

The default histogram is selected on the menu (AP Hip) prior
to exposure. The correct exam must be selected.
 Histograms: Image Rescaling
Digital Frequency
Rescaled Histogram

0 Digital Value 2048

The luminance values of each pixel have now been adjusted to
match the default histogram for an AP Hip.
Histograms: Image Rescaling

Raw Image Rescaled Image

Note that this image still does not possess the
proper brightness and contrast that you would
expect from an AP hip.
 Histograms: Image Rescaling
 During this phase of image formation, an
algorithm is applied that will modify the
luminance values to model a characteristic
histogram for that exam.
 The region of interest (ROI) is identified and
the collimated borders around the ROI are
established.
 Histograms: Image Rescaling
 Next, pixel values located outside the ROI are
removed from the raw data.
 The histogram begins as a bar graph and
consists of only values of interest (VOI).
 The VOI are now compared to a default
histogram for an AP Hip and an adjustment is
made.
 This process will change the brightness and
contrast of the image.
 Look-up-tables:
 Brightness and contrast are further refined by
the use of look-up-table (LUT) algorithms for
digital radiography.
 Look-up-tables:
Rescaled Image Final Image

Look-up-table Algorithm
 Look-up-tables:
2048

Processed Image Pixel Value

1024

0
0 1024 2048
Pixel Values from the Rescaled Image
 Look-up-tables:
Rescaled No Change from
Image Original Image

AP Hip
Look-up-Table
Algorithm

No Adjustment to Original Pixel

Value from the Histogram
 Look-up-tables:
2048

Processed Image Pixel Value

1024
850

0
0 1024 2048
Pixel Values from the Rescaled Image
 Look-up-tables:

Processed Pixels
Original Pixels

45 11
AP Hip
600 Look-up-Table 725
Algorithm
1420 2011

AP Hip
Look-up-Table
Algorithm

Rescaled Image Final Image

 Histogram & LUT Summary:
Raw Image Rescaled Image Final Image

Histogram LUT
Image Quality vs. CR Image Processing:

kVp: 55 65 75
mAs: 5 2.3 1.2
S#: 111 109 106
Contrast 2.68 2.68 2.68
Note how image quality remained fairly constant.
 Digital Optimum kVp Values:
Chest (Grid) 110 to 130
Chest (Non Grid) 80 to 90
* Be sure to follow
Abdomen 80 to 85
hospital protocol.
Abdomen (Iodine) 76 to 80 *
Extremities (Non Grid) 65 to 75 **
Extremities (Grid) 85 to 95 ** If possible, avoid
AP Spines 85 to 95 using less than 1
Lateral Spines 85 to 100 mAs during any
Ribs 80 to 90 exposure.
Skull 80 to 90
Barium Studies 110 to 120
Modified from Barry Burns
 ALARA: Dose Creep
 Konica S# Range: 100 to 400
kVp mAs S# Tube Output
80 75 107 321 mR
80 38 211 164 mR
80 20 406 87 mR
*92 10 409 60 mR
Total Reduction in Tube Output: 535%
Total Reduction in Patient Dose???
*Using the 15% Rule will decrease tube output by
approximately one third.
 Konica S# Range 100 to 400

kVp 80 80 80 92
mAs 75 38 20 10
S# 107 211 406 409
mR 321 164 87 60
Note how image quality remained fairly constant.
 Spatial Resolution:
 Controlled by the following:
Size of the Matrix
Pixel Size
Field of View (FOV)
Detector Element Size for DR
Sampling Frequency for CR
 Spatial Resolution:
 Matrix
Made of columns and rows of cells (pixels).
 Spatial Resolution:
 Pixel (Picture Element)
They are generally square.
 Voxel (Volume Element)

Pixel Voxel
 Spatial Resolution:
 Pixel Pitch
Refers to the distance between each pixel.
 Pixel Size vs. Matrix Size:
Large Medium Small

If the FOV remains constant and the size of the

matrix is increased, the pixel size & pitch will
decrease thereby increasing the spatial resolution.
Pixel Size vs. Matrix Size:
Large Medium Small
 Spatial Resolution vs. FOV:

24 x 30

35 x 43
Note how the pixel pitch has changed.
Which FOV has the highest spatial resolution?
 Spatial Resolution vs. FOV:
 Some manufactures will decrease the pixel
pitch as the FOV is reduced.
 The same number of columns and rows are
packed into a smaller FOV.
 The original matrix is maintained within the
smaller FOV and results in an increase in
spatial resolution.
 Spatial Resolution vs. FOV:

24 x 30

35 x 43
Since the pixel pitch remains the same, the spatial
resolution is unchanged.
 Spatial Resolution vs. FOV:
 Other manufactures maintain the same pixel
pitch as the FOV is reduced.
 The net result is a decrease in the size of the
matrix while the pixel size remains the same.
 Bottom line: there is no change is spatial
resolution.
CR Spatial Resolution:
A thinner diameter laser
will create a higher
sampling frequency.

A higher sampling
frequency will decrease
pixel pitch and result in
higher spatial resolution.
CR Spatial Resolution:
 CR Spatial Resolution:

The high resolution mode will increase the

sampling frequency.
 CR Spatial Resolution:
 PSP imaging system spatial resolution is
determined by the sampling frequency.
 Sampling is performed by the laser and ADC.
 The diameter of the laser controls the
sampling frequency.
 A higher sampling frequency will result in less
pixel pitch and therefore smaller, more
densely packed pixels (larger matrix).
 CR Spatial Resolution:
 The spatial resolution for CR is approximately
2.5 LP/mm.
 High resolution CR can produce images with
up to 5.0 LP/mm.
 DR Spatial Resolution:
 The smaller the detector element (DEL) size,
the higher the spatial resolution.

Image Receptor DEL Size Resolution

Direct Capture DR 100 µm 5 LP/mm
Indirect Capture DR 140 µm 3.7 LP/mm
Indirect Capture DR 200 µm 2.5 LP/mm

If the size of the DEL is doubled, the spatial

resolution is reduced by half.
SpatialSize
Matrix Resolution Comparison:
& Typical Bit Depth:
Image Receptor DEL Size Resolution
Film/Screen NA 10+ LP/mm
Direct Capture DR 100 µm 5.0 LP/mm
High Resolution CR NA 5.0 LP/mm
Indirect Capture DR 140 µm 3.7 LP/mm
Indirect Capture DR 200 µm 2.5 LP/mm
General Use CR NA 2.5 LP/mm
 Modulation Transfer Function (MTF):
 Each component of the imaging system
contributes to the overall system performance.
 MTF is a ratio of how accurately the object is
produced on the image as a function of spatial
frequency.
A perfect imaging system would have an
MTF equal to 1 or 100% and is not
achievable.
Modulation Transfer Function (MTF):
High MTF Low MTF

Note how the image quality is reduced as the

MTF is decreased.
 Quantization:
 Refers to the numerical value assigned to each
pixel to represents patient anatomy.
 This value is dependent upon pixel bit depth.
Pixel bit depth is the number of shades of
gray that each pixel can produce.
 The pixel bit depth is determined by the ADC
employed by each manufacturer.
 This is the foundation for grayscale.
 Pixel Bit Depth: n
 Based on the binary numbering system (2 ):
Bits Shades of Gray
22 4
28 256
210 1,024
212 4,096
214 16,384
216 65,536
The human eye can discern 100 shades of gray.
 Pixel Size
Matrix Bit Depth by Modality:
& Typical Bit Depth:
Modality Matrix Size Bit Size
MRI 256 x 256 16
CT 512 x 512 16
DR 3000 x 3000 16
CR 3520 x 4280 12
Digital Mammography 4096 x 4096 12
Note how as the size of the matrix is increased,
the bit size is decreased.
 Receptor Contrast:
 Refers to the fixed ability of the IR to record
exposure data.
 Contrast resolution is the smallest exposure
change or signal difference that can be
detected by the IR.
This is directly related to dynamic range
which is the range of exposures that can be
captured by a detector.
 Dynamic range and quantization are a
product of the bit depth of each pixel.
 Receptor Contrast:
 Exposure latitude is the range of exposures
which produce quality images at appropriate
patient dose.
Most IRs have essentially a linear response
to exposure.
 Exposure Latitude:
CR Latitude

F/S Latitude
Saturation

Density
Brightness

Quantum Noise

Exposure in mR
 Quantum Noise:

Desired Image Quality Quantum Noise

 Saturation:

Saturation takes 8-10 times the normal exposure and

produces flat, black areas on the image.
 Exposure Latitude:
 Bottom Line:
mAs and kVp are used to reduce quantum
noise, avoid saturation, and ensure adequate
penetration.
Signal-to-Noise Ratio (SNR):
Matrix/Pixel Size
Large Medium Small

Low Medium High

Image Noise
 Signal-to-Noise Ratio (SNR):
 Signal refers to useful image information.
 Noise refers to the accumulation of quantum
noise (dose) and electronic interference.
 A high SNR is desirable.
 As pixel size decreases, the amount of signal
capture decreases and thus the SNR decreases.
 Manufactures must balance pixel size and
SNR in order to provide optimal spatial
resolution.
Detective Quantum Efficiency or DQE:
 This refers to how well an imaging system
converts the exit beam into an output image.
 DQE is affected by receptor contrast (contrast
resolution, dynamic range, bit depth) and the
signal-to-noise ratio.
 A high DQE will provide the ability to image
small, low contrast anatomy.
Detective Quantum Efficiency or DQE:
 DQE ranked from highest to lowest:
Direct Capture DR
Indirect Capture DR
CR
 Preprocessing Image Manipulation:
 Flat-fielding is used to automatically remove
artifacts (noise) that form fixed patterns.

An example would be corrections to remove

the anode heel effect.
 Preprocessing Image Manipulation:
 Dead pixel correction refers to making
corrections for non responsive pixels.
Pixel interpolation is used to estimate the
value of the defective pixel.
 Preprocessing Image Manipulation:
 Dead pixel correction refers to making
corrections for non responsive pixels.
Pixel interpolation is used to estimate the
value of the defective pixel.
 Post-processing Image Manipulation:
 Generally, you want to keep these to a
minimum before your images are sent to PACS.
 Shuttering, Masking or Cropping
Process of replacing excess light caused by
collimation around an image with a black
background to eliminate veil glare.
 Post-processing Image Manipulation:
 Edge Enhancement (hard changes)
This algorithm increases the contrast around
the edge of an object.
The increase in contrast makes the object
appear to be more defined.
This should be used sparingly because it can
increase noise and cause a halo artifact.
Post-processing Image Manipulation:

An edge enhancement algorithm has be applied to

the lower potion of this image. Note the appearance
of a halo around the edges.
 Post-processing Image Manipulation:
 Smoothing (soft changes)
Uses an algorithm to make small reductions
in image noise.
This algorithm cannot compensate for
images that possess large amounts of noise.
When too much noise is present, there is not
enough data available to improve the image.
If this is the case, the image should be
repeated.
 Post-processing Image Manipulation:
 Windowing is the process of changing the pixel
brightness and contrast
Window level changes pixel brightness.
Window width changes the overall image
contrast.
Effects of Window Level:
Effects of Window Width:
 Inversion:
2048

1024

0
0 1024 2048
 Inversion:
2048

1024

0
0 1024 2048
Inversion:
Inversion:
 Equalization:
 This is also referred to as Dynamic Range
Compression (DRC).
 An algorithm is employed to reduce file size by
subtracting the extreme light and dark areas of
the image.
 The remaining dynamic range will be modified
to improve the overall contrast of the image.
 Equalization:

Dynamic Range

Compression (cropping)

The contrast is slightly modified to improve the

overall image quality.
 Equalization:
No DRC With DRC

The final image has been compressed to reduce file

size and has an improved level of contrast.
 Odds and Ends:
 Picture Archiving and Communications
Systems (PACS)
Consists of a network system that links
imaging devices, digital archives and
display workstations
 Digital Imaging and Communications in
Medicine (DICOM) Images
Standard image configurations employed by
digital imaging venders for PACS
 Part II: An Overview of Image
Production & Technical Evaluation
 Radiographic Quality:

Visibility Properties Geometric Properties

Brightness Contrast Distortion Spatial Resolution

Shape Size

Foreshortening Elongation Magnification

The Brightness Unit
 Brightness:
 Measurement of the luminance displayed on a
monitor for a radiographic image.
Calibrated in units of candela (cd) per square
meter.
 Receptor exposure (RE) and computer
algorithms work together to produce the
brightness level required to display the image.
 This unit will focus on factors that affect the RE.
 Milliamperage or mA:
 What function does the mA setting perform?
 In general, how accurate are the mA settings?
 It is the primary controlling factor for controlling
RE.
 mA has a direct and proportional relationship on
RE.
mA RE
100 15 mR
200 30 mR
400 60 mR
 Exposure Time (ms) or (s):
 What function does the time setting perform?
 How accurate is the timer?
 Why is time not the primary controlling factor for
RE?
 Exposure time has a direct and proportional
relationship on RE.
Time RE
50 ms (0.05 s) 15 mR
100 ms (0.1 s) 30 mR
200 ms (0.2 s) 60 mR
 mAs:
 Has a direct and proportional relationship on RE.
 Reciprocity Law
mA Time mAs RE
100 200 ms (0.2 s) 20 60 mR
200 100 ms (0.1 s) 20 60 mR
400 50 ms (0.05 s) 20 60 mR
Which of the above techniques would be optimal
for a small child?
The reciprocity law requires calibrated
equipment.
 Kilovoltage Peak or kVp:
 This is primarily a measurement of beam quality
but it does affect beam quantity (intensity) to a
lesser extent.
 What is the primary controlling factor for beam
quantity?
 If you increase the kVp, will more electrons be
produced at the filament?
 Will more x-rays be produced at the anode?
 Kilovoltage Peak or kVp:
 Optimum kVp
 Be mindful that no amount of mAs can
compensate for a lack of adequate kVp.
 Optimum kVp:

Abdomen
* **
* IR **
10 mAs at 50 kVp 20 mAs at 50 kVp
 15% Rule:
 To maintain the RE, increase the kVp by 15% and
reduce the mAs by 50%.
Using the 15% Rule in this manner will reduce
tube output by approximately one third.
 How will reducing the kVp by 15% and doubling
the mAs affect the RE?
How about the patient dose?
 15% Rule:
 The 15% Rule vs. RE and tube output:
kVp mAs Tube Output RE
115 5 40 mR 30 mR
100 10 60 mR 30 mR
85 20 80 mR 30 mR
 What might be another clinical application for this
rule?
 15% Rule:
 How would you change the following technique if
you wanted to use kVp to help reduce motion but
maintain the original RE?
80 kVp 100 mA 200 ms (0.2 s)
80 kVp x 1.15 = 92 kVp
200 ms x 0.5 = 100 ms
New Technique: 92 kVp 100 mA 100 ms (0.1 s)
 The Anode Heel Effect:
 X-rays are emitted isotropically from the anode.
 The intensity of the beam decreases as you travel
closer to the anode side of the tube.
The Anode Heel Effect:

Cathode
Stator
(-)
Target
Anode (+)
Filament
Focusing Cup
 The Anode Heel Effect:
Stator Anode
(+) Focusing Cup

Anode “Heel” e-e-

e-e-
e-
e-e- (-)
e-e-

Engage the Rotor:

Thermionic Emission
 The Anode Heel Effect:
Stator Anode
(+) Focusing Cup
* e-e-
* e- e-
e-
* * e- e- e- e-
Anode “Heel”
* * e- e- e- e- e-e-e-
* e- e-
e-
e- e-e-e- e-
e-
e- e- e-e-e- e-e- (-)
* e- e- e- e- e-
e-e- e- e-e- e- e- e-e-
e- e- e- e- e- e-
e- e- e- e- e-
e- e- e- e- e-
Close the Circuit
The Anode Heel Effect:
 Added Filtration:
• Any filtration beyond that which is inherent.
• Thin sheets of aluminum (Al) are added to the
port of the x-ray tube.
• The primary function is to decrease patient skin
dose.
Added Filtration:
Added Filtration: Konica CR
2.5 mm 3.5 mm 4.5 mm 5.5 mm

S = 374 S = 393 S = 584 S = 634

As the Al filtration was increased, the S value also
increased. This indicates a decrease in RE.
X-ray Tube Port:
The X-ray Emission Spectrum:
With No Filtration
At 90 kVp
Quantity or
Intensity of
X-ray
Photons

69.5
69 90
X-ray Photon Energy (keV)
The X-ray Emission Spectrum:
With 2.5 mm of
Filtration At 90 kVp
Quantity or
Intensity of
X-ray
Photons

30 69.5
69 90
X-ray Photon Energy (keV)
Added Filtration vs. the X-ray Emission Spectrum:
What happened
What happened to the beam intensity?
to the
average energy of the
How about
primary beam? the RE?

Quantity or
Intensity of 2.5 mm
X-ray
Photons
3.5 mm

30 69.5
69 90
X-ray Photon Energy (keV)
Collimation vs. RE:

Patient

IR
Image

Tight Collimation
Collimation vs. RE:

Patient

IR
Radiographic Image

* No Collimation *
Collimation vs. RE:

Patient

IR
Radiographic Image

* No Collimation *
Collimation vs. RE: Magnified
IR

Radiographic Image

* *
No Collimation
Collimation vs. RE: Magnified
IR

Radiographic Image

*
Bottom Line:
*
Lack of collimation adds
unwanted scatter (noise) to the IR.
Collimation vs. RE: Konica CR
24 x 30 cm Collimation No Collimation

S = 142 S = 103

The lower S value is the direct result of an increase

in RE caused by a lack of collimation.
 The Inverse Square Law:
 The intensity (mR) of the beam is inversely
proportional to the square of the distance between
the source and the image receptor.
 This formula is employed to determine changes in
beam intensity at a new distance.
I1 D22
I2 D12
I1 = old mR D1 = old distance
I2 = new mR D2 = new distance
 The Inverse Square Law:
 The following version of this formula may be
employed to determine changes in beam intensity.

new mR = old mR old SID 2

new SID
 The Direct Square Law:
 This formula is employed to maintain beam
intensity at a new distance

I1 D12
I2 D22

I1 = old mR D1 = old distance

I2 = new mR D2 = new distance
 The Direct Square Law:
 The following versions of this formula can be
employed to maintain beam intensity at a new
distance

new mAs = old mAs new SID 2

old SID
 Example #1:
 If your original beam intensity was 5.0 mR at a 30” SID,
what would be your new beam intensity if the SID was
changed to 60”?
•
new mR = old mR old SID 2

new SID

new mR = 5.0 30” 2

60”

new mR = 1.25 mR
 Example #2:
 Your original SID was 40” and 75 mAs produced an
acceptable RE. What new mAs would you use at 60” if
you wanted to maintain the original RE?
•
new mAs = old mAs new SID 2

old SID

new mAs = 75 60” 2

40”

new mAs = 168.75

 Radiographic Grids:
 First invented by Gustav Bucky in 1913.
 It was later refined by Hollis Potter in 1920 by
adding a side-to-side motion to blur the grid lines.
 It become known loosely as a Potter-Bucky Grid.
 Grid Construction:
 Grids consist of alternating lead strips and
interspace material.
 The greater the angle of the incident scatter, the
more likely that the scatter radiation will be
absorbed.
Angle of Incident Scatter:

Patient
* *
*
Grid
*
IR
 Grid Construction:
 Grid Frequency
 Grid Ratio (GR)
The height of the lead strips is divided by the
distance between them.
GR = h/D
With all other grid construction factors
constant, the higher the GR, the greater the
scatter clean-up.
Higher GRs also require more accuracy in their
use and result in a higher patient dose.
Grid Ratio Calculation:
H
H == 24
4.0mm
mm
GRGR= =h/D
H/D
GRGR= =4.0/0.5
24/4
GRGR= =8:1
6:1
DD==0.5
4 mm
mm 6060Lines/Inch
Lines/Inch
H
H ==24
4.0mm
mm
GR
GR == 4.0/0.25
24/1
GR
GR == 16:1
12:1
120
120 Lines/Inch
Lines/Inch
DD = 2 mm
= 0.25 mm
 Grid Construction:
 Grid Radius or Focal Range
Parallel vs. Focused Grids
 Parallel Linear Grid:

72”
SID

IR
 Focused Linear Grid:

72”
SID

IR
 Grid Cap:

Front Back
Grid Cap: Magnified

Front
 Grid Cap: Magnified

Ratio: 8:1
Focus: 40 to 72
LPI: 132
The LPI range for digital IRs is between103 and 200
with 140 being the average.
Grid Cut-Off:
 Patient Factors to Consider:
 Additive Diseases
Require a 50% increase in mAs or a 7.5%
increase in kVp to maintain RE
Additive Disease: Ascites

 Normal  Ascites
 Patient Factors to Consider:
 Destructive Diseases
Require a 30% decrease in mAs or a 5%
decrease in kVp to maintain RE
Destructive Disease: Osteoporosis

 Normal  Osteoporosis
Patient Factors to Consider: Casts
 Fiberglass: increase mAs by 30% or increase
kVp by 5%
Patient Factors to Consider: Casts

 Original Technique: 60 kVp @ 1.2 mAs

Patient Factors to Consider: Casts

 New Technique for Fiberglass:

 63 kVp @ 1.2 mAs
Patient Factors to Consider: Tissue Opacity
 Determined by the atomic number of the cells that
comprise the anatomy of interest
Patient Factors to Consider: Tissue Opacity

 Hollow vs. Solid Organs

Patient Factors to Consider: Tissue Opacity

 Contrast Agents
 Patient Factors to Consider:
 Body Habitus
Hypersthenic
Sthenic
Hyposthenic
Asthenic
The Contrast Unit
 Subject Contrast:
 The magnitude of the signal difference in the
remnant beam as a result of the different
absorption characteristics of the tissues and
structures making up that part.
 The difference in the thickness and atomic
numbers of the structures that comprise the body
part of interest.
 kVp is the primary controlling factor for subject
contrast.
This is the basis for optimum kVp.
Image (Radiographic) Contrast:
 The visible difference between any two selected
brightness levels within a displayed image.
 It is determined by algorithms that are applied to
raw data collected during image capture.
Image (Radiographic) Contrast:
 Grayscale
The number of brightness levels or shades of
gray visible on an image.
Linked to the bit depth of the system which a
reference to the total number of shades of gray
available.
How would noise affect grayscale?
Image (Radiographic) Contrast:
 Short Scale or High Contrast
Major differences between shades of gray.
 Long Scale or Low Contrast
Slight differences between shades of gray.
 kVp dictates the starting point for image contrast.
All other factors that impact image contrast
will cause it to increase or decrease from here.
Image (Radiographic) Contrast:

High Contrast = Short Scale = Few Shades of Gray

Low kVp

Low Contrast = Long Scale = Many Shades of Gray

High kVp
Image Contrast: Film/Screen

Note the
relationship
between kVp
and subject
contrast.

50 kVp 100 kVp

Image Contrast: Konica CR
CR algorithms
work to maintain
a similar scale of
contrast even at
different levels
of kVp. A
difference in
contrast, albeit
not as dramatic,
does still exist.
50 kVp 100 kVp
Collimation vs. Contrast:

Patient

IR
Image

Tight Collimation
Collimation vs. Contrast:

Patient

IR
Radiographic Image

* No Collimation *
Collimation vs. Contrast:

Patient

IR
Radiographic Image

* No Collimation *
Collimation vs. Contrast:
IR

Radiographic Image

* *
No Collimation
Collimation vs. Contrast:
IR

Radiographic Image

*
Bottom Line:
*
Lack of collimation adds
No Collimation
unwanted scatter (noise) to the IR.
Collimation vs. Contrast: Konica CR
24 x 30 cm Collimation No Collimation

S = 142 S = 103

The lower S value is the direct result of an increase

in RE caused by a lack of collimation. Note the
change in image contrast.
Added Filtration vs. the X-ray Emission Spectrum:
What
What happened
happened to the to the average
energy
average ofofthe
energy the primary beam?
primary beam?
What will happen to contrast?
Quantity or
Intensity of 2.5 mm
X-ray
Photons
3.5 mm

30 69.5
69 90
X-ray Photon Energy (keV)
Filtration vs. Contrast: Konica CR
2.5 mm 3.5 mm 4.5 mm 5.5 mm
 Filtration vs. Contrast: Konica CR
2.5 mm 5.5 mm

The scale of contrast slowly decreases as Al filtration is

increased. CR algorithms minimize the effect.
 OID vs. Contrast:

Patient
What happens *
to contrast?

Patient 4” OID
*
1” OID

10 mAs at 75 kVp
IR 20 mAs at 75 kVp
OID vs. Contrast: Konica CR
4” OID 10” OID

Note how the 10” OID image is slightly brighter

indicating a shorter scale of image contrast.
 Grids vs. Contrast:
What would
Patient happen to
contrast if you
changed to a
* * larger grid?

*
8:1 GR
*
IR
Grids vs. Contrast: Konica CR
6:1 Grid Ratio 15:1 Grid Radio

S = 259 S = 257

Note the improvement in image contrast with the

higher grid ratio.
 Patient Factors to Consider:
 Body Habitus
 Additive vs. Destructive Diseases
 Casts
The Spatial Resolution
Unit
 Spatial Resolution (SR):
 i.e. Sharpness of Detail
 Sharpness of the structural edges recorded in the
image.
The ability to visualize sharp lines on a
radiographic image.
 Measured in mm of unsharpness which indicates
the level of image SR.
 Is a geometrically sharp image possible to
achieve?
 Motion:
 Single most detrimental factor
 Voluntary vs. Involuntary
 Motion vs. SR:

Voluntary Involuntary
 Geometric Factors:
1. Focal Spot (FS)
2. Object-to-Image-receptor Distance (OID)
3. Source-to-Image-receptor Distance (SID)
4. Source-to-Object Distance (SOD)
 Geometric Factors:
 Focal Spot
Primary controlling factor for SR.
Only variable that exclusively affects SR.
Generally, techniques > 200 mA will require a
large focal spot.
Penumbra vs. Umbra
--
Focal Spot Size vs. SR:
0.6 mm FS 2.0 mm FS

Patient

IR
--
FS Size vs. SR: Konica CR
Small FS Large FS
 Geometric Factors:
 OID
Of the geometric factors, this is the most
critical factor to consider.
What is the overall MOST critical factor to
consider regarding SR?
--
OID vs. SR:
2.0 mm FS 2.0 mm FS

Patient 4” OID
1” OID

IR
 OID vs. SR: Konica CR
1” OID 4” OID 8” OID
--

Note how the SR decreases as the OID is increased.

--
SID vs. SR:
72” SID

40” SID

Patient

IR
 SID vs. SR: Konica CR
40” SID 60” SID 72” SID

CR algorithms work to maintain a similar level of SR.

A difference in SR, albeit slight, does exist.
Geometric Unsharpness Formula:
 This formula is employed to determine how much
unsharpness is created for a given set of technical
factors
FS x OID
SOD
 Example #1:
 How much geometric unsharpness is created when
the following factors are employed for a lateral
c-spine?
1. 2.0 mm FS
•
2. 10” OID
3. 72” SID
2 x 10
= 0.32 mm of unsharpness
62
The penumbra spreads across an area of 0.32 mm.
 Example #2:
 How much geometric unsharpness is created when
the following factors are employed for a PA chest?
1. 1.0 mm FS
•
2. 4” OID
3. 72” SID
1x4
= 0.06 mm of unsharpness
68
The penumbra spreads across an area of 0.06 mm.
Which example produced the highest resolution?
 SR vs. Visibility Properties:
 SR has no effect on Brightness and Contrast.
The Distortion Unit
 Distortion:
 Can distortion ever be totally eliminated from the
image?
 Consider the effect of placing a three dimensional
object on a two dimensional image receptor (IR).
•
•
Size Distortion vs. OID: Konica CR
1” OID 4” OID 8” OID

OID is the most critical

factor affecting size distortion.
Size Distortion vs. SID: Konica CR
40” SID 60” SID 72” SID

Size distortion will decrease as the SID in increased.

How would you use SID to offset the magnification
created by OID?
Methods to Calculate Magnification:
1. Magnification Factor or
2. Degree of Magnification Formula
 Magnification Factor (MF):
 Image magnification can be assessed by
calculating the ratio between SID and SOD.
MF = SID/SOD
Image Size = MF x Object Size
 Example #1:
What is the image size if the object size is 20”, the
SID is 40”, and the OID is 4”?
MF = 40/36
MF = 1.11
(The image size will be 11% larger than the
object size.)
Image Size = 1.11 x 20
Image Size = 22.2”
Degree of Magnification Formula:
Image Width SID
=
Object Width SOD
 Example #2:
What is the image size if the object size is 20”, the
SID is 40”, and the OID is 4”?

x 40
=
20 36
36x = 800

x = 22.2” Image Width

Percent of Magnification Formula:
Image Width - Object Width
100
Object Width
 Example #3:
 Using the data gathered from Example #2, the object
width was 20” and the image width was 22.2”.
What is the percent increase in magnification that
•
was produced for this exposure?
100
22.2 - 20
x 100 = 11%100
20100
 Shape Distortion:
 Shape distortion may result in a misrepresentation
of the anatomical areas of interest.
Elongation vs. Foreshortening
 How to prevent shape distortion:
Ensure that the body part is parallel to the IR.
The CR must be perpendicular to the IR.
Assure proper tube angulation.
-Tube angles may be employed to
desuperimpose pertinent anatomy.
Shape Distortion:
Shape Distortion:
Size Distortion vs. Shape of Distortion:
 Size distortion does not increase the level of shape
distortion present in an image.
 However, size distortion will make shape
distortion easier to recognize.
Distortion vs. Visibility Properties:
 Distortion has no effect on either image brightness
or contrast.