Model Based Iterative Reconstructions represent a paradigm shift - - - PowerPoint PPT Presentation

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Sep 20, 2022 124 likes •542 views

Model Based Iterative Reconstructions represent a paradigm shift - Imaging with almost no noise Jonas Rydberg, M.D. Professor of Radiology Indiana University School of Medicine Indianapolis, Indiana Medical Director Radiology IU Health

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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 jrydberg@iuhealth.org

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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 jrydberg@iuhealth.org

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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 jrydberg@iuhealth.org

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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 jrydberg@iuhealth.org

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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 jrydberg@iuhealth.org

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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 jrydberg@iuhealth.org

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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 jrydberg@iuhealth.org

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FBP / IR MBIR

MBIR – A challenge for radiologists

Hard to accept this look

Jonas Rydberg jrydberg@iuhealth.org

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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 jrydberg@iuhealth.org

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MBIR FBP / IR

Can you handle the truth?

The difference is reduced noise!

Jonas Rydberg jrydberg@iuhealth.org

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Texture?! Is there such a thing as “texture” in CT images?

Jonas Rydberg jrydberg@iuhealth.org

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“Texture”

Jonas Rydberg jrydberg@iuhealth.org

Random page from Radiographics 2013

Please, take a few seconds to review the “texture” of mets and liver parenchyma.

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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 jrydberg@iuhealth.org

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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.

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Does fluid in urinary bladder have “texture”? Which image is closest to the truth?

IR MBIR

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What shall fluid in the stomach look like? Like IR or MBIR? The same question then regarding liver!

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IR MBIR

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What shall kidneys look like?

Maybe MBIR depiction is closest to truth?

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IR MBIR

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How about the air around the patient?

FBP IR MBIR

Jonas Rydberg jrydberg@iuhealth.org

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FBP IR MBIR

How about the air around the patient?

Jonas Rydberg jrydberg@iuhealth.org

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Texture? There is no such thing as “texture” as we have always believed.

It is just noise to varying degrees!

Jonas Rydberg jrydberg@iuhealth.org

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Texture of a renal cancer

CT140015501

IR MBIR

Cancer + noise

There are multiple black and white noise pixels projecting

ver the tumor that we take

for texture of the mass.

Cancer

Jonas Rydberg jrydberg@iuhealth.org

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“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

n 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).

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MBIR improves diagnostic quality. The following examples intend to show how MBIR improves the diagnostic quality over FBP and IR.

Jonas Rydberg jrydberg@iuhealth.org

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8 mm cyst in liver Depiction superior with MBIR

8 mm

IR MBIR

Jonas Rydberg jrydberg@iuhealth.org

Unenhanced scan with slice thickness = 4 mm

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IR - “White noise” degrades depiction of both the center and the border of the cyst

IR MBIR

Jonas Rydberg jrydberg@iuhealth.org

Compare “Avg HU” and “SD”

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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

Jonas Rydberg jrydberg@iuhealth.org

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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.

Jonas Rydberg jrydberg@iuhealth.org

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FBP IR MBIR

Jonas Rydberg jrydberg@iuhealth.org

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IR MBIR FBP

Which technique depicts cysts the truest?

Jonas Rydberg jrydberg@iuhealth.org

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IR MBIR FBP

Jonas Rydberg jrydberg@iuhealth.org

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IR MBIR FBP

Jonas Rydberg jrydberg@iuhealth.org

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Jonas Rydberg jrydberg@iuhealth.org

IR MBIR FBP

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IR MBIR FBP

Jonas Rydberg jrydberg@iuhealth.org

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IR MBIR

Jonas Rydberg jrydberg@iuhealth.org

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IR MBIR

Jonas Rydberg jrydberg@iuhealth.org

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IR MBIR

4 mm 1 mm 4 mm 1 mm

Jonas Rydberg jrydberg@iuhealth.org

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Between yellow arrows clear border delineating higher and lower density tissues.

Jonas Rydberg jrydberg@iuhealth.org

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Jonas Rydberg jrydberg@iuhealth.org

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Jonas Rydberg jrydberg@iuhealth.org

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Jonas Rydberg jrydberg@iuhealth.org