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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