Lower kV Imaging and Noise Reduction Techniques - Research ...

120 kV
CTDIvol = 24.5
mGy
Lower kV Imaging and Noise
Reduction Techniques
J. G. Fletcher, MD
Mayo Clinic Rochester
80 kV
CTDIvol = 5.2
mGy
With Imagebased
Denoising

Disclosures
• Grant support - Siemens, Genentech,
Abbott, Centocor
• Lifeng Yu
• Shuai Leng
Acknowledgments
• Cynthia McCollough
• Garrett Spencer
• Amy Hara
• Jeff Fidler
• Jim Huprich
• David Hough

http:// mayoresearch.mayo.edu/ctcic/educational-
resources.csm

Overview
•Dose Reduction
• mAs
• Manual adaptation
• AEC
• kV selection
•Noise reduction methods
• Different approaches
• Observer performance

The Grand Scheme
kV Selection & Noise Reduction
• Will not reduce dose as much as
eliminating…
� unjustified exams
� superfluous acquisitions (e.g.,
unenhanced, delayed)
• Should facilitate (not hinder)
accomplishment of diagnostic task
• Performed with mAs reduction

Differences in Commercial
Implementation of AEC
From Yu et al. Imaging in Medicine 2009

Tube Current Reduction
Original Full Dose
50% Dose Simulation
75% Dose Simulation
25% Dose Simulation

mAs Reduction:
CT Enterography
Routine Image Reconstruction
∆ Qual Ref mAs 240 => 160 mAs
Thicken Slices 2 => 3 mm

mAs Reduction:
CT Enterography
Routine Image Reconstruction
Prior protocols uses 400 & 440 mA => NI 31
Thicken slice 2.5 => 3.7 mm

Low kV
80 kV 120 kV
• Majority of abdominal CT scans: 120 kV
• It is possible to reduce to 80-90 kV
• Why should we use it?
• When should we use it?
• How can I use lower kV to reduce
radiation dose?

(CT Number)
Contrast
300
250
200
150
100
50
0
How does kV affect iodine
enhancement?
Iodine Contrast vs. kVp
60 80 100 120 140 160
kVp
Patient
size
Small
Medium
Large
From Bodily et al. RSNA 2008
• Iodine att’n at 80
kV twice that of
140 kV
• Relative to iodine
att’n at 120 kV
• 70% higher at
80 kV
• 25% higher at
100 kV

linear attenuation coefficient
(1/cm)
100000.0
10000.0
1000.0
100.0
10.0
1.0
0.1
How does kV affect water
enhancement?
80
kV
140
kV
0 50 100 150
x-ray energy (keV)
Water
Cortical Bone
Pure Iodine
Courtesy Dr. Lifeng Yu
Bruesewitz et al. RSNA 2009
• Relative contrast
changes only hold
for high atomic
number
substances
• Iodine, barium
• NOT water,
soft tissue,
calcium

Increased Contrast
2 cc/s, 120 kV 2 cc/s, 80 kV (DS)
2 weeks apart

Relative Contrast Differences due to
Iodine Also Increase at Low kV
120 kV 100 kV

Improved Disease Conspicuity
140 kV 80 kV
Macari M et al. AJR 2010

Relative Contrast Differences due to
Iodine Also Increase at Low kV
80 kV
45 HU diff lesion
lesion-liver liver
120 kV
21 HU diff lesion
lesion-liver liver

Reduced Radiation Dose
120 kV, CTDI vol=5.18 mGy 100 kV, CTDI vol=3.98 mGy
Lower-kV Benefits –
Reduced Radiation Dose

Increased Noise and/or Artifacts
140kV
80kV

Increased Noise & Artifacts
40 cm lateral width 40 cm lateral width
80 kV CTDI vol = 21.4 mGy 120 kV CTDI vol = 21.4 mGy

Benefits
• Increased iodine
signal
• Increased relative
contrast differences
(conspicuity)
• Ability to compensate
for suboptimal IV
contrast
• Radiation dose
reduction
Low kV
Risks
• Increased noise
• Increased potential
for artifacts
• At 80 kV, tube
current limits or pitch
can be a problem
• Minor effect – focal
spot size is slightly
larger
Individual assessment of each patient and diagnostic task

kV Reduction: Clinical Use
• Limited IV access
• Limited contrast dose
• Subtle attenuation differences
===================================
• Young patients
• Small and medium-sized adult patients
(lateral width from CT scout ≤ 41 cm)
Can I do both?
Dosematched
Dosereduced

Low kV
Patient Selection
• Issue is noise (patient size)
• Organ of interest
• Measurements of size
• 116 pts undergoing 80 kV CT
• 2 – 3 mm slices
• IQ, artifact, confidence
• Multiple pt size measures

Low kV
Patient Selection
Patient Size and Acceptability
• Lateral width the best predictor of acceptable
image quality
< 36 cm => 80 kV imaging acceptable
< 41 cm => 100 kV imaging acceptable
• Larger patients may not be able to undergo low
kV imaging
• Patient size selection only insures good quality

Dose-matched Low kV
To Preserve Image Quality
Restaging unresectable Islet Cell tumor
Chest CT at 80 seconds (to avoid compromise of abdominal timing)
100 kV Chest

Dose-matched Low kV
To Preserve Image Quality
Unresectable pancreatic cancer with foot swelling
3 minute delayed 80 kV images show CFV clot
Portal phase image

Dose-matched Low kV
To Preserve Image Quality
Triple-phase 100 kV
enterography with 80 cc
Omnipaque 300 due to solitary
kidney
Reduced IV Contrast
80 kV CT enterography
CR = 1.4, 80 cc Omnipaque 300 w/ NS flush

Dose-matched Low kV
To Preserve Image Quality
Reduced Contrast Injection Rate
80 kV enterography 2° to compromised venous pedal access (2 cc / s)
SCAN AT 85 seconds

Dose-matched Low kV
To Preserve Image Quality
• Locate a dose-matched kV table for your
scanner (two are located at the end of this presentation)
• Perform 120 kV topo & insure width at
liver < 41 cm
• Prescribe scan volume & record CTDI vol
• Change kV to 100 kV
• Plug in dose-matched mA from table
• If 2 cc/s, delay scanning to 85 sec for
portal phase

Low kV to Lower Radiation Dose
120 kV
17.3 mGy
100 kV
7.71 mGy
• kV and dose-matched mAs to get the lower dose
• Iodine CNR allows you to give up dose & tolerate noise

Low kV Imaging While Reducing Dose
• Need to consider both patient size and
diagnostic task into kV selection process
• Greater the iodine contrast differences,
the greater ability to reduce dose for
smaller pts
• kV selection combined with lowering mAs
(from dose-matched mAs)
• Creates a new technique chart for each
diagnostic task
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.

General Strategy for kV selection
• Iodine CNR is a not a sufficient image quality
index
• Must also constrain image noise
• We already know what noise levels we can
tolerate
CNR ≥
CNRref
, and σ ≤ α •
ref
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.
σ

Lower kV for Dose Reduction
• 80 kV prescribed using vendor kV selection tool
• mA chosen to stay within noise limits
• 25% dose reduction

General Strategy for kV selection
Consider 80 kV imaging
Contrast by 70%
Here’s the idea
Improved contrast permits the noise level to increase
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.

General Strategy for kV selection
Consider 80 kV imaging
Contrast by 70%
Noise by 70%
Here’s the idea
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.

General Strategy for kV selection
Consider 80 kV imaging
Contrast by 70%
Noise by 70%
Here’s the idea
≥ Contrast 120
Noise 120
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.

General Strategy for kV selection
Consider 80 kV imaging
Contrast by 70%
Noise by 70%
Here’s the idea
≥ Contrast 120
Noise 120
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.

General Strategy for kV selection
Consider 80 kV imaging
Contrast by 70%
Noise by 70%
Here’s the idea
≥ Contrast 120
Noise 120
Increased noise permits the dose reduction
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.

General Strategy for kV selection
Consider 80 kV imaging
Contrast by 70%
Noise by 60%
Here’s the idea
≥ Contrast 120
Noise 120
As patients get larger (or task requires less noise), the
acceptable increase noise (σ) becomes smaller
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.

General Strategy for kV selection
Consider 80 kV imaging
Contrast by 70%
Noise by 50%
Here’s the idea
≥ Contrast 120
Noise 120
As patients get larger (or task requires less noise), the
acceptable increase noise (σ) becomes smaller
L. Yu, H. Li, J. Fletcher, C. McCollough, Medical Physics, 37(1), 2010.

General Strategy for kV selection
Consider 80 kV imaging
Contrast by 70%
Noise by 40%
Here’s the idea
The dose reduction will also decline
≥ Contrast 120
Noise 120
As patients get larger (or task requires less noise), the
acceptable increase noise (σ) becomes smaller

• Math is involved
Low kV
Reduce Radiation Dose
• Two pathways
• Technique charts that prescribe both
kV and mA for a given task
• Commercial kV selection tools
• Over a large number of patients, dose is
reduced by about 20 - 30%

CTDIvol (mGy) per 100 effective mAs
14
12
10
8
6
4
2
0
GE VCT CTDIvol/100mAs on scanner
GE VCT CTDIvol/100 mAs from square conversion (use 120kV
as reference)
Siemens Flash CTDIvol/100mAs on scanner
Siemens Flash CTDIvol/100mAs from square conversion (use
120kV as reference)
kV2 kV2 kV2 kV2 kV2 kV2 kV2 kV2 80 100 120 140
Tube Potential (kV)
The widely used relation “Radiation output CTDIvol is proportional to kVp 2 for the same
mAs” is not accurate.
As shown above, the actual CTDIvol at 80 kVp is about ~50% lower on both GE and
Siemens scanners for the lower kV’s

Low kV
Reduce Radiation
Dose
Dose reduction percentage
Practice
Implementation
40.0
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
28 33 38 43 48
Later width (cm)
16 – 30% dose savings
Depending on Pt size
kV 80
kV 100
Right to Left
Patient Width kV Relative Dose Factor
25 80 0.65
26 80 0.66
27 80 0.68
28 80 0.69
29 80 0.71
30 80 0.73
31 80 0.73
32 100 0.74
33 100 0.74
34 100 0.75
35 100 0.75
36 100 0.78
37 100 0.81
38 100 0.83
39 100 0.86
40 100 0.89
41 100 0.92
42 100 0.94
43 100 0.97
44 120 1
45 120 1
46 120 1
47 120 1
48 120 1
49 120 1
50 120 1
51 120 1
52 120 1
53 120 1
54 140 0.96
55 140 0.87

Auto kV Look-up Table
CT Enterography, 80 kV
CTDIvol 5.5 mGy
Patient lateral width: 25 cm (liver)
30 cm (pelvis)
Dose reduction 31%

Commercial kV Selection
• Based on iCNR and task-specific noise
levels
• Takes complex relationship of pitch, kV,
generator size (kW), and tube current
(mA) limits into account

Radiation dose reduction
Commercial kV Selection
50%
40%
30%
20%
10%
0%
-10%
-20%
80 kV 100 kV 120 kV 140 kV
Routine Abdominal CTA
• kV changed in 73% cases
•Overall 30% dose reduction, but depends on
patient size
• iCNR and EQC identical in subset with
comparisons @ 120 kV despite dose savings
Courtesy Dr. Lifeng Yu
50
45
40
35
30
25
Patient lateral width (cm)
Radiation dose reduction
Routine Abdominal CT
•Overall 20% dose reduction, but depends on
patient size
•iCNR and EQC identical in subset with
comparisons @ 120 kV despite dose savings
60%
50%
40%
30%
20%
10%
0%
43
scans
75
scans
44
scans
162
scans
80 kV 100 kV 120 kV Overall

100 kV, 23% dose reduction c/w 120 kV
100 kV, 26% dose reduction c/w 120 kV

120 kV
(CTDIvol 18.89 mGy)
100 kV
(CTDIvol 7.13 mGy)
Routine Reconstruction
More dramatic dose reductions can be achieved if
we permit noise levels to increase further

mAs Reduction:
CT Enterography
Sensation 64
Siemens Scanners
∆ Qual Ref mAs 240 => 160 mAs
Thicken Slices 2 => 3 mm
Table replaced with CarekV
(vendor kV selection tool) where
available

mAs Reduction:
CT Enterography
GE Scanners
Prior protocols uses 400 & 440 mA
Thicken slice 2.5 => 3.7 mm

Noise Reduction
to Reduce Image Noise
(and make lower dose more pleasant)
120 kV
18.89 mGy
100 kV
7.13 mGy
100 kV + IRIS
7.13 mGy
Routine dose and noise
Excessive noise
Lower dose and similar
noise
Image-based noise reduction (IRIS, Siemens Medical Solutions)

Noise Reduction
to Reduce Image Noise
(and make lower dose more pleasant)
Half-Dose Denoised B43 Full Dose

Reduce Dose and Make Diagnosis
Adapt for Patient and Diagnostic Task
mA, kV, Noise Reduction
Full dose – 120 kV & 240 Qual Ref mAs Half dose – 120 kV & 120 Qual Ref mAs
+ Noise Reduction

Noise Reduction
Increases Fidelity to a Higher Dose Image
Routine Dose + FBP
Daniel 69305159
Low Dose + ASIR
15 mSv 6 mSV
Iterative Noise Reduction Method (ASIR, GE Healthcare)
Courtesy Dr. Amy Hara

Noise Reduction Methods
Iterative Noise Reduction Methods (ASIR)
• Singh, Kalra, Hsieh et al. Radiology 2010; 257:
373 - 383
• 22 pts
• 4 additional scans @ 50 – 200 mAs,
reconstructed with FBP & 30 – 70 % ASIR
• No lesions missed on FBP or ASIR images
• Significant improvement in noise, IQ,
conspicuity at lowest dose level
• No loss of contrast or sharpness

Image Noise Reduction
Common Themes
• Noise reduction can improve image quality &
confidence*
• There are always trade-offs
• Noise and dose reduction
• Performance can be preserved for a variety
of tasks at very low doses**
• Unclear if CT noise reduction improves
observer performance
* Singh Radiology 2010, Sagara AJR 2010, Prakash Inves Radiol 2010
** Allen AJR 2009, Kambadakone AJR 2009, Siddiki Inflamm Bowel Dz 2009

Finding the Low-dose Sweet Spot
• Finding the low dose “sweet spot” the radiologist’s responsibility
• Reducing the noise without artifacts or minimizing conspicuity of
subtle structures and lesions is the manufacturer responsibility
Courtesy Dr. Cynthia McCollough

Finding the Low-dose Sweet Spot
?
Courtesy Dr. Cynthia McCollough

The Challenge
Original Dose ½ Dose + Half Noise Dose Reduction
Are we missing anything?
Is Noise Reduction Improving Diagnosis?

Denoising and Dose Reduction
Observer Performance
Lee, Park, et al. AJR 2011 (in press)
• 92 pts
• FD, ½ dose, ½ dose with
noise reduction
• ½ dose = 3.5 mGy CTDIvol
• Evaluated imaging findings
of inflammation at TI
• 1/2 dose with and without
noise reduction found
agreement with full dose in >
85% of cases

There are other reasons to
consider or adopt noise
reduction
Image quality,
Confidence & Fatigue

Noise Reduction
Trade-offs
Noise
0.6
0.5
0.4
0.3
0.2
0.1
Full Dose CT + FBP
0
0
-0.1
1 2 3 4 5 6 7 8 9 10
Spatial Frequency (lp / cm)
Courtesy Dr. Amy Hara

Noise
Noise Reduction
Trade-offs
0.6
0.5
0.4
0.3
0.2
0.1
0
Half Dose CT + FBP
Full Dose CT + FBP
0 1 2 3 4 5 6 7 8 9 10
-0.1
Spatial Frequency (lp / cm)
Courtesy Dr. Amy Hara

Noise
Noise Reduction
Trade-offs
0.6
0.5
0.4
0.3
0.2
0.1
0
-0.1
Half Dose CT + FBP
Half Dose CT + 40% ASIR
Full Dose CT + FBP
0 1 2 3 4 5 6 7 8 9 10
Spatial Frequency (lp / cm)
Courtesy Dr. Amy Hara

Effect of % ASIR
No ASIR = FBP 40-50% ASIR 100% ASIR
NOISE
Same dataset, CTDI=9
ASIR
Courtesy Dr. Amy Hara

Noise Reduction
Trade-offs
• Noise texture – blotchiness or pixelated
• Can be minimized by
• Strength or blending settings
• Selection of dose
• Depends on method, but often minor and
reader effect idiosyncratic
Singh et al. Radiology 2010
Prakash Invest Radiol 2010
Lee et al. AJR 2011 (in press)

Noise Reduction Strategies
• Reconstruction kernel
• Image and projection-space
denoising
• Iterative reconstruction
• Iterative noise reduction
methods

Image Reconstruction
Acquisition
Projection Data
PS Filter
Image
Reconstruction
• Filtered Back
Projection
(reconstruction
kernel)
• Iterative
Reconstruction
Iterative Noise Reduction Methods (ASIR,
SAFIRE)
CT image
Imagespace
Noise
Reduction
Filtered CT
image

Noise Reduction
Reconstruction Kernel in Analytical Reconstruction
Original 3D Edge Preserving
Noise Reduction
61.5 HU
- 41%
36.3 HU
Courtesy of R. Raupach

Noise Reduction
Reconstruction Kernel in Analytical Reconstruction
B43 B40

Noise Reduction
Image-space Denoising
• Linear or non-linear filters directly applied
on the reconstructed images
• Tend to change the appearance of CT
images (noise texture)
• Potentially to sacrifice low-contrast
detectability, if the filter strength is not
well controlled
• Performance requires careful evaluation for
each diagnostic task

Integration of Noise Reduction on a
Departmental Basis
PACS
Noise Reduction
Within Image
Reconstruction System

Integration of Noise Reduction on a
Departmental Basis
Image-based Noise Reduction
PACS

Comparison of 4 image-based noise reduction methods
(1/2 dose CTE)
Original B40
IRIS I40
SharpView A81
IRIS2 B30

Differences in Image-based Noise Filters
SharpView Careful Noise Reduction SharpView Subtraction
Mayo Image-based Noise Filter* Mayo Image-based Noise Filter*

Image-based Denoising
Image Quality Improvement

Projection Space Denoising
Bilateral filtering - smoothes the image,
with weights determined according to
• Proximity & intensity similarity
• Models and predicts noise
• Useful to consider benefit of noise
reduction with lower kV
Manduca et al. Med Phys 2009

Projection Space Denoising
80 kV Non-Denoised CTE
80 kV Projection-space Denoised
CTE
Diagnostic quality achieved by reducing dose by half with kV/mAs reduction
followed by noise reduction
Guimaraes et al. Acad Radiol 2010

Projection Space Denoising
B43 Denoised 80kV
Low kV Low dose + PS DN
B40 Mixed kV
3/3 readers rated conspicuity same/greater for ½ dose low kV with PS DN

Full dose blended Half dose 80 kV
80 kV + PS 80 kV + PS/IS
80 kV + PS/MBF
Paulsen et al ARC 2010

Iterative Reconstruction
• Models CT system geometry (e.g., beam spectrum,
noise, beam hardening effect, scatter and incomplete
data sampling).
• Different degrees of credibility among projection data
are allowed
• Noise models based on photon statistics and other
physical properties of the data acquisition
• May improve spatial resolution and reduce image
artifacts such as beam hardening, windmill, and metal
artifacts
• Can be independent of analytical reconstruction
• High computation load
• Usually used in a misleading fashion for marketing

Iterative reconstruction
Projection
Data
Compare
& update
Simulated
Projection data
Iteration loop:
Optimize an
objective function
Projection
(System model)
Modified
Data
Image
Backprojection
Backprojection
Final
Image

Iterative Reconstruction
Advantages:
Physical effects Noise Models
Beam spectrum
Noise
Beam hardening
Scatter
Incomplete sampling
More accurate
Lower image noise
Improve spatial
resolution
Reduce artifacts

69895464
Ultra low dose with MBIR
MBIR = Model based iterative reconstruction
Example: CT at 10 mAs (routine = 200 mAs)
FBP 50% ASIR
MBIR
64 x 0.625, helical pitch 1, 120kVp
Same pt, same scan
(MBIR, GE Healthcare) Courtesy Dr. Amy Hara

Iterative reconstruction
Potential for Practice
Full Dose 50% Dose 60% Dose 80% Dose
Pilot study
21 pts, proven liver and pancreatic lesions, 3 readers
IQ and lesion conspicuity scores overall better using Prototype IR reconstruction
at 50% dose
Ehman et al. SGR 2010

Iterative Noise Reduction Methods
that Utilize Projection Data
• ASIR (Adaptive Statistical Iterative
Reconstruction, GE Healthcare)
• Takes into account photon statistics
and image noise
• Blends ASIR & FBP image to userprescribed
degree
• FDA approved and greatest clinical
experience

Iterative Noise Reduction
Impact on Implementation & Image Quality
• Sagara, Hara, Pavlicek, et al. AJR 2010; 195:
713 – 719
• 53 pts with prior CT exams
• Compared dose & image quality utilizing a
lower-dose acquisition (NI: 22 → 31)
followed by recon using 40% ASIR
• Overall 33% reduction in dose (25 → 17 mGy
CTDIvol)
• Lower-dose ASIR: ↓noise, ↓sharpness, =
diagnostic acceptability

Iterative Noise Reduction
Impact on Implementation & Image Quality
17 mGy CTDIvol
40% ASIR
3.75 mm slices
27 mGy CTDIvol
FBP
From Sagara, Hara, Pavlicek, et al. AJR 2010; 195: 713 – 719

Low Dose CTE with ASIR: 4 mSv
43 yo F BMI = 19
Courtesy Dr. Amy Hara

Iterative Noise Reduction
Impact on Implementation & Image Quality
• Prakash, Kalra, Kambadakone et al. Invest Radiol 2010;
45: 202 – 210
• Retrospective, case-control design
• Used weight-based AEC settings, with NI increased
for the patients on whom 40% ASIR was performed
• 156 ASIR patients, 66 FBP patients
• Overall 26% dose reduction for lower AEC settings
• ↓noise with ASIR
• At this level of dose reduction, ASIR images had ↑
IQ in large pts, = IQ in smaller pts

Iterative Noise Reduction
Impact on Implementation & Image Quality
Flicek et al. AJR 2010
• Phantom & human study
(18 pts)
• 50 mAs supine vs. 25 mAs
prone + ASIR
• Lower dose ASIR
acquisition – no difference in
2D or 3D IQ

Iterative Noise Reduction Methods
that Utilize Projection Data
• SAFIRE (Sinogram-affirmed IR, Siemens
Medical Solutions)
• Iteratively compares an image in
which noise has been detected &
subtracted with model-based forward
projection
• Under FDA review, not approved
currently

Iterative Noise Reduction
Impact on Implementation & Image Quality
• Krueger et al. SGR 2011
• 40 pts, 3 readers
• Comparison of full-dose, ½ dose, ½ dose with
SAFIRE (CTDIvol = 13.8 and 6.8 mGy)
• Assessment: IQ, Organ detection & confidence,
significant findings
• All diagnostically acceptable
• IQ: Full > ½ dose (in pelvis: ↑SAFIRE)
• Reader confidence: idiosyncratic
• Significant Findings: varied by reader, not dose or
reconstruction

Improved Image Quality Does ≠ Improved Observer Performance
Subtle Dz Neo-terminal ileum and Perianal Fistula Can be seen on half –dose ± SAFIRE (2 mm slice
thickness, corresponding to 3.3 mGy), even though IQ markedly improved

CT Dose Reduction:
Implementation into Practice
2 mm slice
Routine wFBP
2 mm slice
SAFIRE
19 yo female
Crohn’s
CTDI vol 3.49 mGy

Comparison of Noise Reduction Methods
IRIS I40 SharpView A81
Original B40
Projection Space 1 SAFIRE
Projection Space 2

Noise Reduction
Future
• Observer performance studies at lower
doses
• Improved methods available
38 yo female
Crohn’s
CTDIvol 6.5 mGy
Standard 13 mGy
PS DN

Conclusions
• Lower dose abdominal CT can be
achieved through a variety of
techniques
• Technique charts, reduced mAs,
AEC, kV selection
• Noisier images can be interpreted
without loss of diagnostic accuracy
• Noise reduction methods improve
image quality of low dose images

Conclusions
• Observer performance studies
needed to define
• benefit of noise reduction at low
doses
• extent of dose reduction possible
Routine B40 kernel
CTDIvol = 3.5 mGy
Iterative Noise Reduction Method

http:// mayoresearch.mayo.edu/ctcic/educational-
resources.csm

Tube Current Reduction
Original Full Dose
50% Dose Simulation
75% Dose Simulation
25% Dose Simulation