Jonas Rydberg, M.D.
Professor of Radiology
Indiana University School of Medicine
Indianapolis, Indiana
Medical Director
Radiology
IU Health Methodist Hospital
Model Based Iterative Reconstructions
represent a paradigm shift
- Imaging with almost no noise
Jonas Rydberg [email protected]
Disclaimer: IU Health Methodist Hospital collaborates with Philips Healthcare on CT imaging.
iDose Iterative Reconstructions (IR)
IMR Model Based Iterative Reconstructions (MBIR)
The experience shared in this presentation is based on work with iDose (IR) and IMR (MBIR) both Philips Healthcare. But, only the terms “IR” and “MBIR” will be used to name the two techniques.
Jonas Rydberg [email protected]
Iterative reconstructions (IR)
- Radiation dose reduction 50% or more
Model Based Iterative Reconstructions (MBIR)
- More radiation dose reduction
- Improve the diagnostic image quality
Conclusions from body imaging
and CTA:
Jonas Rydberg [email protected]
CTDIvol (mGy)
4.81
CTDIvol (mGy)
5.74
CTDIvol (mGy)
17.5
300 mAs 98 mAs 71 mAs
Iterative reconstructions (IR):
Same patient scanned using IR on different occasions with
different reference mAs. Significant dose reductions possible.
Jonas Rydberg [email protected]
Radiation dose reduction Abdomen-Pelvis with IR
FBP: 120 kVp Ref mAs 300 19.6 mGy IR: 120 kVp Ref mAs 173 11.8 mGy
Radiation dose reduction
= 40 %
(More recently we have moved the Reference mAs to 154 = 50% radiation dose reduction.)
Jonas Rydberg [email protected]
Radiation dose reduction Abd/Pel with MBIR
FBP: 120 kVp Ref mAs 300 19.6 mGy IR: 120 kVp Ref mAs 173 11.8 mGy MBIR: 100 kVp Ref mAs 154 6.7 mGy
Radiation dose reduction
= 66 %
Jonas Rydberg [email protected]
There are no extreme cases of radiation dose reduction presented here. All cases in this presentation were scanned with our standard IR (iDose level 4) kVp = 120 kVp Reference mAs = 173 or higher The purpose was to explore if MBIR could add diagnostic quality instead of just reducing the radiation dose.
Jonas Rydberg [email protected]
FBP / IR MBIR
MBIR – A challenge for radiologists
Hard to accept this look
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Even tougher challenge with non-enhanced scans
MBIR
Bland
Water colors
“Monet effect”
FBP / IR
Radiologist reactions:
Not right
Waxy
Texture missing Jonas Rydberg [email protected]
MBIR FBP / IR
Can you handle the truth?
The difference is reduced noise!
Jonas Rydberg [email protected]
“Texture”
Jonas Rydberg [email protected]
Random page from Radiographics 2013
Please, take a few seconds to
review the “texture” of mets
and liver parenchyma.
Random page from Radiographics 2013
“Texture”
For the past 30 years I have been convinced that I have viewed the texture in both liver parenchyma and metastasis.
“Am I wrong?”
Jonas Rydberg [email protected]
FBP IR MBIR Filtered back projection Iterative reconstructions
Model Based Iterative reconstructions
”Texture” of liver metastasis
Somewhat strangely the ”texture” decreases with MBIR. Likewise strangely the texture of the metastasis and the liver parenchyma seems to be the same on both FBP and IR.
Does fluid in urinary bladder have “texture”? Which image is closest to the truth?
IR MBIR
130167039
What shall fluid in the stomach look like? Like IR or MBIR?
The same question then regarding liver!
130167039
IR MBIR
What shall kidneys look like?
Maybe MBIR depiction is closest to truth?
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IR MBIR
Texture?
There is no such thing as “texture” as we have always believed.
- It is just noise to varying degrees!
Jonas Rydberg [email protected]
Texture of a renal cancer
CT140015501
IR MBIR
Cancer + noise There are multiple black and white noise pixels projecting over the tumor that we take
for texture of the mass.
Cancer
Jonas Rydberg [email protected]
“Black noise” and “White noise” Reducing image noise has been one of the major goals for the CT development during the past 35 years. We are so used of seeing noise that we barely are aware of it. It has gone so far that the noise reduction with MBIR can creates confusion radiologists. Noise destroys the diagnostic quality of the images. To better understand the negative effect of noise in FBP and IR I think in terms of “Black noise” and “White noise”. That will be discussed in the following cases. Please, note that the black and white noise is an expression that I have adopted based on my own observations. You may see it expressed in other terms in the literature. The “noise” is typically quantified and expressed in standard deviations (SD).
MBIR improves diagnostic quality.
The following examples intend to show how MBIR improves the
diagnostic quality over FBP and IR.
Jonas Rydberg [email protected]
8 mm cyst in liver
Depiction superior with MBIR
8 mm
IR MBIR
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Unenhanced scan with slice thickness = 4 mm
IR - “White noise” degrades depiction of both the center and the border of the cyst
IR MBIR
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Compare “Avg HU” and “SD”
If slice thickness is decreased to 1 mm noise hurts the IR technique
IR MBIR
MBIR is noise resilient even
at 1 mm slice thickness
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IR MBIR
4 mm slice thickness depicts cyst better than
1 mm but there is a price to pay with
increased partial volume averaging.
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FBP IR MBIR
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IR MBIR FBP
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IR MBIR FBP
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Jonas Rydberg [email protected]
IR MBIR FBP
IR MBIR FBP
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IR MBIR
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IR MBIR
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Between yellow arrows clear border delineating higher and lower density tissues.
Jonas Rydberg [email protected]
Jonas Rydberg [email protected]
Jonas Rydberg [email protected]
Jonas Rydberg [email protected]