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DUAL SOURCE CARDIAC CT ANGIOGRAPHY
Dr Ravi Mathai, MD.
Consultant Radiologist,
Dar Al Shifa Hospital
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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
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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.
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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
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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
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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
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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
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Goals of CTA primary goal diagnostic IQ
second goal - low dose
protocol aims at the above
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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
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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.
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Contraindications to CTA Contrast hypersensitivity (absolute)
Renal failure (absolute)
Poor breathhold
AF
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Breathold Breathe in -- breathe out – breathe in – hold your breath (13 seconds)
Patient training
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Heart rate for S64 - <60
for DSCT <95
look for ectopics, arrythmias
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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
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ECG ECG -must be noise free
Gating - prospective and restrospective
Scan protocols
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Noisy
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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
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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
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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
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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)
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Scan modes Scan mode selection - prospective, retrospective, pulse off, flash.
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ECG controlled dose modulation - retrospective
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ROI AA for test and care bolus
extend for bypass grafts
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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%
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Multiphase reconstructions
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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
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Adaptive ECG-Pulsing -ECG-Controlled Dose Modulation for Cardiac Spiral CT
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Adaptive Cardio Sequence -ECG-Triggered Sequential CT
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ADAPTIVE
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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
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FLASH
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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.
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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
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Kv modification as per weight
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sub mSv CTA
100kv
320mAs
120mm scan range
flash mode
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FLASH
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pediatric protol
Flash mode
80kv
104mAs
120mm scan range
Dose less than 1mSv
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FLASH
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Image processing 2d images MIP best for diagnosis
3d complementary
stenosis grading - software Syngovia - automatic calculation.
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Graft
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Stenosis
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HR 85 Prospective
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HR 83 Retrospective
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Stent
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Pediatric
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Adaptive with arrythmia
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FLASH
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FLASH
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FLASH
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TEAM CTA