How do the Parameters affect Image Quality and Dose for Abdominal CT? Image Review

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1 How do the Parameters affect Image Quality and Dose for Abdominal CT? Image Review Mannudeep K. Kalra, MD, DNB Massachusetts General Hospital Harvard Medical School

2 Financial Disclosure This presentation was made possible with support from RSNA R & E Foundation s Education Scholar Grant GE Healthcare: Faculty for Master Course on Radiation

3 Learning Points Understand effects of scan parameters on abdominal CT images Apply knowledge of image and lesion appearance to make indication specific CT protocols.

4 Lungs: Lack of Effect at Lower Dose 270 mas 20 mgy 135 mas 10 mgy 70 mas : 5 mgy 35 mas : 2.7 mgy 18 ma s : 1.3 mgy

5 Lungs = High Contrast = CT Colonography Low Dose

6 CT Colonography: High Contrast = Lower Dose mas: kv Flat polyp (8 mm) 2-4 mgy

7 What else is high contrast in Abdomen? High contrast = Kidney stones Calcium Vs Soft tissues Lower Dose

8 Kidney stone CT: Seen at Lower Dose FBP 300 mas 140 kv 30 mgy 350 mas 120 kv 24 mgy 200 mas 120 kv 13 mgy 65 kg BMI mas 120 kv 7 mgy 50 mas 120 kv 3.4 mgy

URINARY STONE CT Tube Potential Tube current (prefer AEC) Image thickness (mm) CTDI vol 120 KV commonly (100 kv< 60 kg) About 30-50% lower than routine abdomen 2.

9 URINARY STONE CT Tube Potential Tube current (prefer AEC) Image thickness (mm) CTDI vol 120 KV commonly (100 kv< 60 kg) About 30-50% lower than routine abdomen 2.5-5mm 2-6 mgy (size based) A B Fixed ma Use AEC (NI 20) (A) CT images of 60-year-old man acquired with fixed current and (B) AEC at NI 20 show a tiny calculus (arrow) in left renal pelvis. AEC (A) enabled 50% dose reduction compared to fixed current technique.

10 Calcium : Seen at Lower Dose Radiodense stones (GB) can also be seen at low dose FBP 300 mas 140 kv 30 mgy 350 mas 120 kv 24 mgy 200 mas 120 kv 13 mgy 100 mas 120 kv 7 mgy 50 mas 120 kv 3.4 mgy

11 Bones- chest or abdomen: Well Seen at Lower Dose 200 mas 12 mgy FBP 150 mas 9 mgy FBP 100 mas 6 mgy FBP 50 mas 3 mgy FBP

12 What else is high contrast in Abdomen? Contrast enhancing Structures (vessels= CTA) Lesions (hypervascular lesions) Lower KV= lower Dose

140 kv 29 mgy Abdominal @ Different KV 120 kv 24 mgy 80 kv 8 mgy Mean HU 120.

13 140 kv 29 mgy Different KV 120 kv 24 mgy 80 kv 8 mgy Mean HU SD: kv 16 mgy Mean HU SD: 13.8 Mean HU SD: 42.9 Mean HU SD: 30.6

Inc. Published by Lippincott Williams & Wilkins, Inc.

14 CTA of Aorta High Contrast CTA allows use of lower KV (non-obese) 100 kv (60 cc) 160 mas 7 mgy 80 kv (60 cc) 260 mas 5 mgy 2009 Lippincott Williams & Wilkins, Inc. Published by Lippincott Williams & Wilkins, Inc. 80 kv (45 cc) 260 mas 5 mgy Schindera, Sebastian et al. Investigative Radiology. 44(10): , October 2009.

15 Multiphase Liver CT: Lower KV + IR algorithm Contrast enhancing lesions: HCC & metastasis 140 kv 300 mas 5 mm FBP 17 msv 80 KV 540 mas 5 mm FBP 5 msv 80 kv 540 mas 5mm Hybrid IR 5 msv IR helps

kv 200-530 mas 5 mm FBP 20 mgy 80 KV 360 630 mas

16 Multiphase Liver: Lower KV + IR Contrast enhancing lesions: HCC & metastasis IR helps 120 kv mas 5 mm FBP 20 mgy 80 KV mas 5 mm FBP 11 mgy 80 kv mas 5mm Hybrid IR 11 mgy

17 Multiphase Exam: Dose Reduction: Liver Arterial phase: Lower kv (100) Liver only coverage AEC PV phase: Usual or Lower kv Longer coverage AEC

18 CT Enterography (CTE): Lower Dose Rel. higher contrast Oral contrast Vs bowel wall FBP 200 mas 7 mgy FBP 100 mas 3.5 mgy IRIS 10 mas 3.5 mgy = Lower Dose 50% of routine CT

19 Routine abdomen CT Higher dose than kidney stones and CTC Lower contrast between soft tissue lesions and soft tissue organs

20 Routine Abdomen: Patient factors and Dose o o o Size: Obese vs average or slim o Use AEC always for ma optimization o Lower kv in smaller patients with contrast CT helps cut dose Arms by the side of the patient o Keep out or Keep above the abdomen with pad not besides Patient motion (voluntary or involuntary) o Pitch > 1; Rotation time < 0.8 second

21 Routine Abdomen: Use AEC Obese 339 mas 23 mgy Average/slim 65 kg 115 kg 200 mas 14 mgy 50 mas 3.4 mgy 200 mas 14 mgy 50 mas 100 mas 3.4 mgy 6.7 mgy

22 633 ma 90 ma 24 mgy 360 ma 3.4 mgy 45 ma 180 ma 14 mgy 1.7 mgy 7 mgy

23 135 mas 10 mgy 270 mas CTDI vol: 20 mgy 18 mas 1.3 mgy Varying mas 120 kv 5 mm, Pitch: 0.9:1 FBP: B30 67 mas 5.0 mgy 36 mas 2.7 mgy

CT For Hematuria: Decreasing Scan Phases Wider x-ray beam 1.25 >> 0.

ml saline drip infusion Wait 15 minutes (Prone) 100 ml IV contrast bolus @ 3 ml/sec. Scan at 100-sec.

24 CT For Hematuria: Decreasing Scan Phases Wider x-ray beam 1.25 >> Pitch ~ or > 1:1 Tube Potential (kv) Tube current Use AEC Unenhanced CT 50 ml IV contrast bolus 250 ml saline drip infusion Wait 15 minutes (Prone) 100 ml IV contrast 3 ml/sec. Scan at 100-sec. delay 46-year-old woman with hematuria. Optimal enhancement of kidneys and adequate opacification and distension of ureters seen. Maher MM, Kalra MK, et al. BJR 2004

25 Non-contrast limit coverage: kidneys to SP Lower dose ( - 50%) AEC Multiphase Exam: Hematuria Post Contrast: Wider coverage AEC

26 CT Appendicitis: Lower Dose Standard Dose: mas AEC 120 kv 122 mgy.cm Lower Dose mas AEC 544 mgy.cm CE CT: 3ml/sec

27 Benign Disease: Young Patients Ex: Appendicitis Limited coverage: L3 to SP AEC for size adapted dose

28 Lower noise: Higher dose Rule out Abdo CT Low contrast lesions Use AEC to optimize Lesion Detection high confidence Higher noise = Lower dose CT colonography CT angiography Kidney stones Hypervascular lesions Use AEC &/ low kv

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