Non-invasive Multislice CT Coronary Angiography

Transcription

1 Non-invasive Multislice CT Coronary Angiography Erasmus Medical Center, Rotterdam, The Netherlands Departments of Radiology en Cardiology Nico R Mollet, MD Filippo Cademartiri, MD Pim J de Feyter, MD

2 Multislice CT Basics

3 Data Acquisition

4 Data Acquisition

5 Data Acquisition

6 Data Acquisition X ray Attenuation Profile Image Reconstruction Detectors

7 Data Acquisition Sequential CT Step-and-Shoot Spiral CT Axial slices obtained Axial slices reconstructed

8 Image Reconstruction -180 GANTRY POSITION +180 PLANE POSITION Z-AXIS

9 Evolution in CT Conventional (Sequential) CT: Axial slices Spiral CT: Volume scanning: Reconstruction of axial slices Multislice or Multidetector Spiral CT: Larger volume in less scan-time

10 Analog-Digital Conversion Acquisition Analog-digital Conversion Digital Reconstruction Storage Archiving Post-processing Quantification Digital-analog Conversion Display

11 Digitization

12 CT Density Values: Hounsfield Units G H Air bubbles Fat Pericardium, thrombus, muscles, plaques Vessel Calc/Clip/Stent Lung Fat Soft tissue CM Bone/Calc T R Air Oil Water Calcium/Metal Density - HU

13 Pitch Pitch 2 Pitch 1 Pitch 0.5 Pitch: (in Multislice CT) Table feed per rotation Total width of collimated beam (n detectors x collimation)

14 Pitch Pitch 2 Pitch 1 Pitch 0.5 Pitch >1: Data gaps (interpolation needed) Pitch =1: Contiguous data Pitch <1: Oversampling of a single object (e.g pitch 0.2: 5x oversampling)

15 Collimation X-ray beam X-ray tube Collimator (fan-shaper) X-ray tube Collimated fan beam Table Feed Detectors Collimator (select detectors) Detectors Longitudinal view Short axis view

16 Collimation DAS DAS DAS DAS

17 Collimation DAS DAS DAS DAS

18 Matrix & Field of View CT matrix: 512 x 512 pixels Field of View Pixel size Matrix size CT slice: 512 x 512 voxels

19 Voxel Size Voxel = 3-dimensional Pixel Isotropic spatial resolution: voxel size equal in x,y,z-axis

20 Spatial Resolution & Partial Voluming Averaging of >1 tissue types within 1 voxel resulting in a weighted density value

21 Synchronization With Cardiac Cycle

22 Synchronization With Cardiac Cycle

23 Synchronization With Cardiac Cycle

24 Synchronization With Cardiac Cycle

25 Synchronization With Cardiac Cycle Prospective ECG Triggering (Sequential) ECG signal triggers the acquisition Cardiac phase is pre-defined

26 Synchronization With Cardiac Cycle

27 Synchronization With Cardiac Cycle Retrospective ECG Gating ECG signal is recorded while the whole volume is acquired Cardiac phase is arbitrary

28 Synchronization With Cardiac Cycle Prospective Triggering Retrospective Gating Sequential Scanning Data acquired at a single, predefined phase of the cardiac cycle Trigger time is based on estimation of the R-R intervals from previous heart beats Sensitive to irregular heart rhythm Min. Temporal Resolution - 250ms Spiral Scanning Data acquired for the entire cardiac cycle - parallel ECG recording True match of the phase reconstruction to the ECG retrospectively Less sensitive to irregular heart rhythm Min. Temporal Resolution - 125ms

29 Synchronization With Cardiac Cycle Same patient: Irregular Heart Rate EBT Sequential Trigger 4-MSCT Spiral Gating Courtesy of University Clinic of Grosshadern, Munich, Germany

30 Multislice CT Coronary Angiography Anatomy

31 Tomographic (Axial) Images

32 Tomographic (Axial) Images

33 Left Coronary Artery

34 Right Coronary Artery

35 Venous Anatomy

36 Myocardium & Valves

37 Anatomical Myocardial Bridging

38 Multislice CT Coronary Angiography Technique

39 The Aim

40 MSCT Coronary Angiography Prerequisites 1. HIGH SPATIAL RESOLUTION Depiction of vessel wall and small coronary branches 2. HIGH TEMPORAL RESOLUTION Reduce motion artifacts 3. FAST COVERAGE Short breath-hold time 4. SYNCHRONIZATION WITH CARDIAC CYCLE ECG-gating for end-diastolic and end-systolic imaging

41 Spatial Resolution RCA 3.9± ±0.5 LM 4.5±0.5 LAD (prox) 3.7±0.4 CX 3.4± ±0.6 LAD (dist) 1.9±0.4 Female : - 9% LV hypertrophy : + 17% Dilated CMP : + 12% Dodge JT Jr., Circulation, 1992

42 Spatial Resolution Courtesy of University Clinic of Grosshadern, Munich, Germany

43 Spatial Resolution Flat Panel Technology Flohr, Herz 03

44 Fast Coverage High resolution MSCT-CA CA 4-MSCTA 64-MSCTA Coll=1.0 mm Rot.=500 ms Coll=0.6 mm Rot.=330 ms s 12 s

45 Fast Coverage 16-slices or more!!!

46 Fast Coverage Nieman, Heart 02

47 Coronary Motion LAD 22.4 mm/s ± 4.0 RCA 69.5 mm/s ± 22.5 CX 48.4 mm/s ± 15 Achenbach, Radiology 02

48 Synchronization with cardiac cycle

49 Synchronization with cardiac cycle 30% 165 ms 65% 165 ms

50 Synchronization with cardiac cycle R Absolute Forward Absolute Reverse ms ms P T S 165 ms

51 Temporal Resolution = ½ Rotation Time ms ms 1

52 Temporal Resolution HR 49 HR 67 HR 82 Nieman, Heart 02 Flohr, Herz 03

53 Temporal Resolution Single segment vs. Multi-segment Image Reconstruction

54 Single segment Data from 1 cardiac cycle ms Temporal resolution = 250 ms

55 Multi segment Data from 2 cardiac cycles Temporal resolution = 125 ms

56 Multi segment Data from 2 cardiac cycles 1 2 >125 Multi-segment is adaptive

57 Multi segment Data from 2 cardiac cycles Flohr, Acad Rad 03

58 Multi segment Temporal Resolution Flohr, Acad Rad 03

59 Temporal Resolution Single-segment vs Bi-segment (high HR) Single Segment Reconstruction 250ms Bi-segment Reconstruction 125msec

60 Temporal Resolution Single segment vs Bi-segment (low HR) Single Segment Reconstruction 250ms Bisegment Reconstruction 125ms

61 Single vs. Multi- Segment Reconstruction Limitations Multi-segment requires a lower pitch Longer scan and higher dose Multi-segment only feasible in consecutive heart beats with equal R-R interval Does not work if small change in R-R

62 Single vs. Multi- Segment Reconstruction Limitations z z - - Position Continuous spiral scan & feed Continuous spiral scan & feed Recon Recon Image data Image data Delay Recon Volume Gaps Pitch must be reduced when using >2-segment reconstruction

63 MSCT Coronary Angiography Prerequisites What do we have?

64 64-slice CT coronary angiography

65 MSCT Coronary Angiography Prerequisites 1. HIGH SPATIAL RESOLUTION (isotropic 0.4 mm 3 ) Smaller coronary branches evaluable More reliable visualization of in-stent lumen 2. HIGH TEMPORAL RESOLUTION Evaluation of entire coronary tree possible in HR<70 bpm 3. FAST COVERAGE Manageable breath-hold hold for nearly all pts Injection of less contrast, higher injection rate ( ml/s) 4. SYNCHRONIZATION WITH CARDIAC CYCLE ECG-editing possible in minor heart rhythm irregularities

66 Patient Preparation Scan Procedure

67 Patient Preparation Phone contact Check for indication Check for contraindication Check for current medication Check for current heart rate

68 Patient Preparation HR>65bpm Contra-indications Asthma AV block Overt Heart Failure 45-60min. 100mg b-blockerb blocker HR<65bpm HR check IV access

69 Patient Preparation Instructions ECG-leads Breath hold / HR check

70 Patient Preparation IV/Injector connect Prepare injector

71 Scan Procedure 1 hour 4 sec Beta-blocker (>70 min -1 ) IV access & ECG leads Overview scan range Contrast injection (CareBolus ) 100 ml Iomeron 5 ml/s API: Breath hold 12s +100 HU

72 Scan Procedure: Bolus Tracking HU Contrast injection 100 ml Iomeron 5 ml/s Transition sec

73 Scan Protocol - slices/rotation: 2 x 32 (S16: 16) - individual detector width: 0.6 mm (S16: 0.75) - rotation time: 330 (S16: 375 ms) - table feed: 3.8 mm/rotation (S16: 3.0) - X-tube voltage: 120 kv - X-tube current: max. 900 mas (S16: max. 700)

74 Image reconstruction Image processing

75 Image Reconstruction - retrospective ECG-gating (editing when necessary) - temporal resolution: 165 ms (single-phase reconstruction) - effective slice thickness: 0.75 mm - increment: 0.4 mm - kernel: medium smooth (b30f) native coronaries sharp (b46f) in-stent lumen or calcified vessels

76 Filtering Axial images and VRT s Measurements, Ca++, Stents MPR, MIP and flexible use B10f-B30f B40f-B60f B30f-B40f

77 Filtering B10f B30f B60f B80f

78 Image Processing MPR MIP VRT Curved MPR MPR: multiplanar reconstructions MIP: maximum intensity projections VRT: volume rendering techniques

79 Limitations & Artefacts

80 Limitations of CT coronary angiography SELECTED PATIENT POPULATION Stable heart rhythm, able to breath hold for 20s, <70 bpm (spontaneous/β-blocker induced) X-RAY DOSE Better images and higher spatial resolution requires higher dose HEAVY CALCIFICATIONS Blooming and partial volume artifacts mask the lumen HIGH AND IRREGULAR HEART RATES Motion artefacts and mis-registration OPERATOR DEPENDENCY Time-consuming and variable diagnostic accuracy

81 Operator dependency Available: Sensitivity: Specificity: PPV: NPV: STD % 96 % 78 % 91 % 3D % 97 % 87 % 99 % Cademartiri, AJC 04

82 Severe calcification

83 Severe calcification

84 High heart rates

85 High heart rates Nieman, Heart 02

86 Respiratory Motion

87 Arrhythmia Premature ventricular contraction after each 4-5 normal cycles

88 Low HR ECG-editing

89 Low HR ECG-editing

90 ECG-editing Extra-systole

91 ECG-editing Missing data

92 ECG-editing

93 ECG-editing: Results Only patients with mild arrhythmia included Available: Sensitivity: Specificity: PPV: NPV: STD % 96% 87% 91% Edit % 96% 87% 97% Cademartiri, AJR (in press)

94 Radiation Exposure

95 Dose Reduction Prospective ECG-tube modulation

96 Dose Reduction Tube Modulation (+) Reduction up to 50% of dose in low heart rates (-) Less reliable in case of mild arrhythmia (-) Unable to reconstruct datasets during early diastolic phase (low-dose area), but often good time interval for evaluation of the RCA

97 Radiation Exposure Estimations / Calculations Flohr, Acad Rad 03

98 Radiation Exposure Estimations / Calculations Exposure Cornerstones: Bi-Plane Chest X-Ray: 0.1 msv EBCT Calcium Scoring: 0.9 msv Diagnostic Coronary Angiography: 2-6 msv Natural Background Radiation: 2-5 msv p.a. 8.6mSv Cardiac MSCT Exposure 0.7mSv 2.6mSv 1.3mSv * 7mSv 3.5mSv * 0.6mSv 2.2mSv 1.1mSv * 4.3mSv * 4-Slice Trigger 2.5mm Score 4-Slice Gating 3mm Score 4-Slice Gating 1.25mm CTA 16-Slice Trigger 3mm Score 16-Slice Gating 3mm Score 16-Slice Gating 0.75mm CTA * ECG-Pulsing Jakobs, Eur. Radiology 02

99 Radiation Exposure Estimations / Calculations male/female (ECG pulsing) Ca Seq. Ca Spiral CT Angio Jakobs (Eur Rad 02): est. 2.0 / MSCT 100 mas 4x2.5mm (1.0 / 1.4) Hunold (Radiol 03): phantom 1-EBCT63 mas 1x3 mm 1.0 / / MSCT 2-400mAs 2 4x1 mm 1.5 / / / Morin (Circ 03): estimations 1-EBCT63 mas 1x3 mm MSCT 150 mas 4x1/1.3 mm Trabold (RoFo 03): phantom 2.9 / / MSCT 300 mas 12x.8mm (1.6) (4.3) Hunold (RSNA 03): phantom 4MSCT 100/default mas 4x1mm 3.0 / / 13.0 Siemens 4MSCT 100/default mas 4x1mm 4.2 / / 15.7 GE 4MSCT 100/default mas 4x1mm 2.4 / / 8.2 Philips 16MSCT 100/default mas 16x.6mm 5.8 / / 18.8 GE