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DUAL SOURCE CARDIAC CT ANGIOGRAPHY Dr Ravi Mathai, MD. Consultant Radiologist, Dar Al Shifa Hospital 1
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Role of CTA risk stratification ; high CAC score + intermediate FRS = reclassified as high risk acute chest pain - presence of stenoses + determine the necessity of further treatment. ruling out stenosis in patients with intermediate pretest likelihood of disease Detect stenotic lesions in symptomatic patients Follow-Up of Percutaneous Coronary Intervention -in-stent restenosis Follow-Up After Bypass Surgery - patency of the bypass graft - in course, anastomotic site and native vessels 2
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Role of CTA exact analysis of anomalous coronary arteries. assess morphology and function eg valvular motion, wall motion, EF, CO. CT angiography (CTA) has high negative predictive value. 3
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Caveats Use of CT angiography in asymptomatic persons as a screening test for atherosclerosis (noncalcific plaque) is not yet recommended Not recommended for acute coronary syndrome 4
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Limitations of CTA overestimate disease severity limited spatial resolution = +-accurate grading of the severity of stenosis Pronounced coronary calcifications motion artefacts trigger artefacts - cardiac cycle phase high image noise can prevent reliable evaluation radiation dose 5
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DSCT advantage High temporal resolution - 0.28 seconds rotation time = temporal resolution of upto 0.75 seconds - at a pitch of 3.2 (FLASH) Mayo Clinic study 2009 showed no differences in quantitative measures of image quality between single-source scans at pitch = 1 and dual-source scans at pitch = 3.2 Regular and low heart rates prerequisite for CCTA by 64 slice MDCT 6
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Flash advantage high pitch (3.2) dual tube quarter rotation data acquisition 0.28s scan time very low dose limitations - obese, high HR >75 8
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Goals of CTA primary goal diagnostic IQ second goal - low dose protocol aims at the above 10
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Components of a cardiac scan: Patient selection Breathold HR Medications Ecg and gating Contrast timing and dose Scan mode selection - prospective, retrospective, pulse off, flash. kV techniques ROI Reconstruction kernels Low dose techniques Image processing 11
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Patient selection CTA rule out in acute chest pain Ruling out stenosis in patients with intermediate pretest likelihood of disease For the assessment of obstructive disease in symptomatic patients For detecting re-stenosis after stent placement Follow-Up After Bypass Surgery -bypass graft - native vessels- Exact analysis of anomalous coronary arteries. 12
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Contraindications to CTA Contrast hypersensitivity (absolute) Renal failure (absolute) Poor breathhold AF 13
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Breathold Breathe in -- breathe out – breathe in – hold your breath (13 seconds) Patient training 14
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Heart rate for S64 - <60 for DSCT <95 look for ectopics, arrythmias 15
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Medications for S64 -Oral ß-Blockers 1 h before scan if heart rate > 60/min e.g., 100 mg Atenolol i.v. metoprolol (up to 6 x 5 mg) if heart rate in CT scanner is still > 60/min for DSCT - no BB required for HR upto 85. 85-105 no BB if dose increased (retropective scan). >105, BB 16
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ECG ECG -must be noise free Gating - prospective and restrospective Scan protocols 17
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Noisy 18
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Standard Scan Protocol - DSCT Collimation 0.6 mm Rotation: 330 ms kV: 120 kV mAs: 400 mAs Pitch: Enter expected heart rate manually ECG Pulsing: 70-70% for heart rates < 65/min 40-70% for heart rates > 65/min Delay: Contrast time + 2 seconds 19
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Contrast Injection 5 ml/s for the duration of the scan At least 50 ml + Follow by 50 ml saline (or 20% contrast) at 5 ml/s 20
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Contrast injection and Bolus Type of CM: Concentration min. 350mg/ ml, better 370mg/ ml Flow rate: average size patients (~70kg / 150lb) 5cc/ sec; larger patients 7cc/ sec i.v. line: min 18g, better 16g Test Bolus: 10cc contrast/ 50cc saline (Care bolus ROI AA, threshold 100HU) ROI : Measure in ascending aorta 21
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Coronary CTA injector options Normal injector: Volume of contrast = scan time x flow rate + 10cc + 50cc saline; min 45cc, max 100cc Dual flow option: Volume of contrast = scan time x flow rate + 10cc contrast 1st phase: total volume of contrast 2nd phase: 50cc of volume (20% contrast + 80%saline) = (10cc contrast + 40cc of saline) 23
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Scan modes Scan mode selection - prospective, retrospective, pulse off, flash. 25
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ECG controlled dose modulation - retrospective 26
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ROI AA for test and care bolus extend for bypass grafts 27
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Reconstruction Reconstruction Slice thickness: 0.6 mm Kernel: B26f (B46 f for Stents, Ca++) Phase: Initially: Best Diast / Best Syst DSCT: Usually 75% R-R best ; Preset: BD, BS, 70%, 75%, 40% S64: Usually 70% R-R best; Preset: 65%, 70%, 35%, 40% 29
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Multiphase reconstructions 30
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low dose techniques 1.“CARE Dose4D” – Real-time Anatomic Exposure Control 2. “Adaptive ECG-Pulsing” – ECG-Controlled Dose Modulation for Cardiac Spiral CT 3. “Adaptive Cardio Sequence” – ECG-triggered Sequential CT 4. “Adaptive Dose Shield” – Asymmetric Collimator Control 5. “Flash Spiral” – ECG-Triggered Dual Source Spiral CT Using High Pitch Values 6. “X-CARE” – Organ Based Dose Modulation 7. “IRIS” – Iterative Reconstruction in Image Space 31
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Adaptive ECG-Pulsing -ECG-Controlled Dose Modulation for Cardiac Spiral CT 33
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Adaptive Cardio Sequence -ECG-Triggered Sequential CT 38
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ADAPTIVE 39
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High pitch -FLASH With a single source CT, the spiral pitch is limited to values below 1.5 to ensure gapless volume coverage along the z-axis. If the pitch is increased, sampling gaps occur With DSCT systems, data acquired with the second measurement system a quarter rotation later can be used to fill these gaps.In this way, the pitch can be increased up to 3.4 40
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FLASH 41
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FLASH ECG-triggered DSCT scan data acquisition and image reconstruction at very high pitch. images reconstructed in this mode with an acquisition time of 250 ms, a temporal resolution of 75 ms, 100 kV and 0.8 mSv. 42
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Modification of protocols Beta Blockers - preferable above HR 85. Saline vs. 20% contrast flush. - full functional assessment 6 (7) ml flow for heavy patients XXL for heavy patients 100 kV for slim patients 43
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Kv modification as per weight 44
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sub mSv CTA 100kv 320mAs 120mm scan range flash mode 45
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FLASH 46
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pediatric protol Flash mode 80kv 104mAs 120mm scan range Dose less than 1mSv 47
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FLASH 48
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Image processing 2d images MIP best for diagnosis 3d complementary stenosis grading - software Syngovia - automatic calculation. 49
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Graft 50
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Stenosis 51
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HR 85 Prospective 52
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HR 83 Retrospective 53
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Stent 54
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Pediatric 55
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Adaptive with arrythmia 57
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FLASH 58
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FLASH 59
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FLASH 60
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TEAM CTA 61
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