Low-dose CT for Pulmonary Embolism

Transcription

1 Low-dose CT for Pulmonary Embolism Gautham Gautham P. P. Reddy, Reddy, MD, MD, MPH MPH University University of of Washington Washington

2 Introduction Introduction CT CT accounts accounts for for > 50% 50% radiation radiation from from diagnostic diagnostic imaging imaging CT CT PA PA can can have have an an ED ED msv msv Dose-reduction Dose-reduction methods methods have have included included manual manual reduction reduction mas mas or or dynamic dynamic adjustment adjustment tube tube current current Reduction Reduction mas mas can can reduce reduce image image

3 Overview Overview Dose Dose reduction reduction strategies strategies Lower Lower mas mas Lower Lower Reduced Reduced Z-axis Z Z-axis coverage coverage ASIR ASIR Prospective Prospective ECG ECG gating? gating?

4 Low Low mas: mas: : Detection Detection ED ED pts pts suspected suspected 180, 180, 90, 90, 45, 45, 22, 22, and and mas mas (eff) (eff) Simulated Simulated Reduced Reduced subjective subjective image image and and diagnostic diagnostic certainty certainty Decreased Decreased sensitivity sensitivity and and PPV PPV MacKenzie, MacKenzie,, AJR AJR 2007; 2007; 189: :1371

5 Simulated Simulated Low Low Dose Dose pts pts Standard Standard mas mas (effective) (effective) Simulated Simulated at at 60, 60, 40, 40, 20, 20, and and mas mas Dose Dose did did not not affect affect frequency frequency of of positives, positives, identified identified vessel vessel size size,, or or inter- interor or intrareader intrareader variability variability Tack Tack et et al, al, Radiology Radiology 2005; 2005; 236: :318

6 Low Low Dose Dose Protocol Protocol pts pts suspected suspected or or Other Other parameters parameters identical identical Higher Higher attenuation attenuation for for Better Better subsegmental subsegmental images images at at No No subjective subjective change change image image and and delineation delineation anatomy anatomy Schueller-Weidekamm Schueller-Weidekamm, Weidekamm,,,, Radiology Radiology 2008; 2008; 241: :899

7 Image Image Quality: Quality: Phantom Phantom Phantoms: Phantoms: thick, thick, intermediate, intermediate, thin thin CT CT phantom phantom at at 80, 80, 100, 100, 120, 120, PA PA attenuation attenuation higher higher lower lower and and thinner thinner phantom phantom No No diff diff CNR CNR for for thin thin / / intermediate intermediate 44% 44% decrease decrease dose dose Increase Increase CNR CNR thick thick Szucs-Farkas Szucs-Farkas, Farkas,, Invest Invest Radiol Radiol 2008;43: ;43:374

8 Image Image Quality: Quality: Patients Patients pts pts (less (less than than kg) kg) Group Group A: A: Group Group B: B: PA PA attentuation attentuation higher higher No No difference difference CNR CNR or or Image Image ED ED lower lower by by 40% 40% Szucs-Farkas Szucs-Farkas, Farkas,, Invest Invest Radiol Radiol 2008;43: ;43:871

9 Protocol Protocol mas mas mm mm collimation collimation sec sec rotation rotation time time pitch pitch / / 16-row 16-row MDCT MDCT Szucs-Farkas Szucs-Farkas, Farkas,, Invest Invest Radiol Radiol 2008;43: ;43:871

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11 Image Image Quality: Quality: Body Body Weight Weight pts pts (less (less than than kg) kg) CNR CNR higher higher pts pts under under kg kg Body Body wt wt did did not not subjectively subjectively affect affect noise, noise, enhancement, enhancement, or or image image Szucs-Farkas Szucs-Farkas, Farkas, Eur Eur Radiol Radiol 2009;19: ;19:938

12 Reduced Reduced Z-axis ZZ-axis Coverage Coverage pts pts Retrospective Retrospective simulation simulation Z-axis Z-axis coverage coverage reduced reduced Aortic Aortic arch arch to to cardiac cardiac apex apex Reduced Reduced by by 37% 37% No No false false negatives negatives less less coverage coverage Kallen, Kallen, Emerg Emerg Radiol Radiol 2010;17: ;17:1070

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14 ASIR ASIR pts: pts: CT CT the the chest chest (not (not CTA) CTA) ASIR ASIR vs vs filtered filtered backprojection backprojection ASIR ASIR reduced reduced effective effective dose dose by by 28% 28% ASIR ASIR resulted resulted less less noise noise Prakash Prakash et et al, al, JCAT JCAT 2010;34: ;34:40

15 Summary Summary Decreased Decreased mas mas can can adversely adversely affect affect image image and and diagnostic diagnostic accuracy accuracy Decreased Decreased can can reduce reduce dose dose and and improve improve attenuation attenuation without without affecting affecting CNR CNR Lowering Lowering Z-axis Z Z-axis coverage coverage can can lower lower dose dose w/o w/o sig. sig. effect effect on on sensitivity sensitivity ASIR ASIR and and prospective prospective gating gating have have potential potential benefits benefits on on radiation radiation dose dose