Download DUAL SOURCE CARDIAC CT ANGIOGRAPHY

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
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