Radiation Exposure in Pregnancy. John R. Mayo UNIVERSITY OF BRITISH COLUMBIA

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1 Radiation Exposure in Pregnancy John R. Mayo UNIVERSITY OF BRITISH COLUMBIA

2 Illustrative Clinical Scenario 32 year old female 34 weeks pregnant with recent onset shortness of breath and central chest pain Query pulmonary embolism Very concerned about radiation exposure to her unborn child Other diagnostic possibilities include: pneumothorax,, cardiac failure, malignancy, normal, etc.

3 Issues PE is a major cause of maternal death Accurate diagnosis important as treatment has specific risks in pregnancy Radiation is a known cause of; fetal malformation, stillbirth, infant malignancy Goal: Accurate diagnosis while minimizing radiation exposure

4 Risk of radiation to fetus Generally agreed that fetal doses greater than 100 mgy or 100 msv require counseling as associated with higher risks These doses essentially never occur in diagnostic imaging practice However, any level of radiation exposure in pregnancy causes anxiety for everyone (mother, family, doctors)

5 Diagnostic Tools for PE D dimer blood test Doppler Ultrasound of the lower limbs Nuclear Medicine Ventilation Perfusion Scintigraphy Contrast enhanced CT pulmonary angiography (CTPA) Pulmonary angiography

6 D Dimer D dimer levels rise through pregnancy By weeks median value is 500 units. However even at 30 weeks, 20% are less than 500, the cut off for PE in our institution Since the is essentially no risk and minimal cost, we routinely obtain it looking for the cases where it excludes PE (<500)

7 Doppler Ultrasound Legs No radiation exposure If leg vein DVT found, anticoagulation will be instituted Simple, easy, fast, accurate No reason not to do it Radiologist intervention may aid timeliness! We require this prior to any exam using radiation in pregnant patients

8 Nuclear Medicine VP Scintigraphy Less sensitive for PE than CTPA Has limited ability to provide alternate diagnosis (e.g. pneumonia, mediastinal mass, cardiac failure, etc) Higher radiation dose to fetus (370 micro G) than CTPA (131 micro G), both tiny doses Far lower dose to maternal breast tissue Radiation decision is; who takes the hit!

9 CTPA Highly accurate for PE and other chest pathologies Delivers a high dose to maternal breast tissue (10-70 mgy) ) compared to 2 view mammogram (3mGy) Minimal dose to fetus since the beam is highly collimated Iodinated contrast media used that requires thyroid testing of baby at delivery

10 Suggested Algorithm D dimer Doppler ultrasound Radiology consult Chest radiograph Abnormal CXR perform CTPA Normal CXR, perform CTPA or VP scintigraphy according to local preference

11 Clinical Case: Results D dimer positive (>500) Doppler ultrasound of the legs, negative CXR:

12 CT Pulmonary Angiogram

13 Diagnosis: Thymoma & PE

14 Thank you

15 Intra - luminal filling defect: central PA

16 Intra - luminal filling defects: target sign

17 Intra - luminal filling defect: tram track sign

18 Vascular cut off sign

19 Wedge shaped peripheral density Ground glass Consolidation

20 Disclosure of Support Funding received from BC Lung Association Canadian Institutes of Health Research (CIHR) Terry Fox Research Institute

21 Overview CTPA technique Diagnostic findings in acute and chronic PE Artefacts in CTPA Evidence supporting CTPA CTV Radiation dose Further questions

22 CT Vascular Anatomy 3 vascular compartments: Central and segmental PA s Single slice CT (1 track) Sub-segmental PA s Multi- slice CT (4, 8, 16, 64 track) Distal vessels, capillary bed not resolved using CT

23 CT volume averaging effect 1 x 1 x 1 mm

24 Technical Goals of CTPA Thin slices 3 x 1 x 1 mm 1 track 1 x 0.6 x 0.6 mm 16 track 1 x 0.5 x 0.5 mm 64 track Scan large regions of the lungs Dense contrast enhancement of blood Inject intravenous contrast 320 mg/ml at 3-43 ml/sec for a total volume of ml

25 Thin slices improve detection of small subsegmental clots 2.5 mm 1.25 mm Ghaye et al, Radiology 2001;219:

26 Interpretation technique Interpret images using a scrolling technique on a workstation Initially use mediastinal settings (W 450 L 35) Widen window and adjust level to see small peripheral vessels (W 600 L 100) Review parenchyma at lung settings (W 1500 L -750)

27 Acute Pulmonary Embolism: Direct signs Diagnostic Findings Intra-luminal filling defect Vessel cut-off CT equivalent of pulmonary angiographic signs of acute PE

28 Saddle embolus

29 Intra - luminal filling defect: central PA

30 Intra - luminal filling defects: target sign

31 Intra - luminal filling defect: tram track sign

32 Vascular cut off sign

33 Suggestive Findings Indirect signs, suggestive of acute PE 1,2 dilated central pulmonary arteries wedge shaped consolidation dilated right ventricle 1. Coche et al, Radiology 1998;207: Shah et al, Radiology 1999;211:

34 Dilated central arteries

35 Wedge shaped peripheral density Ground glass Consolidation

36 Non enhancing wedge shaped consolidation

37 Dilated right ventricle

38 Chronic PE findings Focal wall thickening Webs and bands Small vessels Hypertrophied bronchial arteries Mosaic perfusion

39 Focal wall thickening

40 Webs and bands

41 Hypertrophied bronchial arteries

42 CTPA Interpretative pitfalls Motion artefact Sub-optimal contrast injection Limited signal to noise Hilar lymph nodes

43 Motion artifact

44 Sub-optimal contrast injection and noise

45 Sub-optimal contrast mixing Yoo et al, RSNA 2003

46 Pseudo vascular cut off secondary to nodes

47 Pseudo vascular cut off secondary to nodes Transverse section Coronal section

48 Sub-optimal examinations Most series report 3-6% 3 rate of sub-optimal examinations 1 Comparable to rate of sub-optimal pulmonary angiograms in PIOPED, 35/1099, 3% 1. Stein et al, Circulation 1992;85:

49 Review of the Evidence Many direct comparisons of spiral CT to: pulmonary angiography VP scintigraphy Systematic reviews Clinical utility studies alternate diagnosis Experimental animal trials

50 Recent Systematic Review Investigated the clinical validity of a negative CT scan in suspected PE 1 Systematic review of studies from 1990 to patients in 15 selected studies 12 single slice, 2 multislice,, 1 EBCT 1. Quiroz R et al, JAMA 295;16:

51 Systematic Review Negative predictive value 99.4% (95% CI 98.7%-99.9%) 99.9%) Negative Likelihood ratio of mortality 0.01 (95% CI ) 0.02) Concluded that the clinical validity of negative CT similar to pulmonary angiography

52 Clinical Utility Trials Increased clinical utility of spiral CT over V-P P scintigraphy 1 diagnosed PE in 23 of 25 cases suggested or confirmed alternate diagnosis in 57 of 85 useful information in 80 of 110, 73% 1. Kim et al, Radiology 1999;210:

53 Metastatic Bone Lesion

54 Animal Trials How good are spiral CT and pulmonary angiography when compared to an external gold standard? Requires an animal trial

55 Motivation: Pulmonary Angiography may be a flawed gold standard Poor inter observer agreement (70%) for limited subsegmental embolism Wide variation in the rate of limited subsegmental embolism 6% 1-30% 2 1. Stein et al, Circulation 1992;85: Oser et al, Radiology 1996;199:31-35

56 True Gold Standard Experiment Spiral CT and pulmonary angiography in 16 anesthetized, ventilated juvenile pigs Embolized subsegmental sized coloured methacrylate beads Spiral CT and pulmonary angiography Methacrylate cast of the pulmonary arteries, providing a true gold standard 1 1. Baile et al, Amer J Resp Crit Care Med 2000;161:

57 C B

58 A 1 2 3

59 RESULTS - CAST 84 of 86 emboli recovered (98%) 5 emboli outside imaged volume 79 emboli for analysis 15 large 18 small 46 combined

60 COMPARISON OF GOLD STANDARDS Sensitivity (%) CT 3 CT 1 Angio Angio Cast

61 COMPARISON OF GOLD STANDARDS Positive Predictive Value (%) CT 3 CT 1 Angio Angio Cast

62 Angiography As Gold Standard Missed 8 emboli (false negative) Incorrectly scored as CT false positives Falsely identified 12 emboli (false positives) Incorrectly scored as CT false negatives Conclusion The use of Pulmonary Angiography as a gold standard can be misleading

63 Outcome Trial Results Both trials showed CTPA acceptable first choice examination for query PE Anderson et al raised the question whether all emboli detected with CTPA require treatment

64 Current Data Suggests 85-90% Sensitive 90-95% 95% Specific Single slice CT, segmental PE Multi-slice CT, segmental and subsegmental PE

65 CT Venography Easy to perform Good patient acceptance Initial reports show good sensitivity and specificity (>90%) compared to ultrasound High gonadal radiation exposure Variable billing strategy

66 CTV Technique 120kVp, 250 mas axial scans 150 ml of 300 mg I per ml non ionic contrast media 5 mm thick slices at 50 mm spacings obtained from pelvis to knees 2 to 4 minutes following CTPA Review using display settings of: width 400, level 40 and narrower width

67 Normal CTV

68 Normal CTV

69 Radiographic Findings Diagnostic findings Intra lumenal non enhancing filling defect Localized non opacification of a vein segment Suggestive findings Enlargment of the vein (venous expansion) Enhancement of the vein wall

70 CTV of DVT

71 CTV of DVT

72 CTV Results CTV added to CTPA identifies more clot Increases the anticoagulation rate by 25% However, the rate of positive PE and DVT in query PE scans is less than 10% Therefore a large number of CTV studies are performed to find a few DVT

73 CTV Controversy Given higher sensitivity of new multidetector row scanners, do we need CTV? If we need CTV, which patients should receive it? Further study is necessary

74 Radiation dose Single slice CT PE dose 3-63 msv Radiation dose mildly increased using 4 and 8 detector row scanners 16, 32, 64 row scanners with dose modulation reduce radiation dose, however image noise is increased More patients are being studied

75 Current issues Significance of isolated subsegmental PE Role of perfusion maps

76 Thank you

77 Clinical Utility Studies Compared spiral CT with V-P V scintigraphy as initial investigation 78 patients outcome: confident diagnosis spiral CT 90%, 35 of 39 V-P scintigraphy 54%, 21 of 39 p<0.001 Cross et al, Clinical Radiology 1998;53:

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