Current and Evolving Clinical Applications of CT in Heart ... · 2/19/2020 3 Multidetector CT Early...

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Current and Evolving

Clinical Applications of CT in Heart DiseaseSREEVATHSAN SRIDHAR, MD

KAISER PERMANENTE, LOS ANGELES MEDICAL CENTER

Objectives

Review history and development of Cardiac CT (Past)

Understand technical parameters in performing Cardiac CT

Recognize appropriate indications for Cardiac CT

Discuss future directions and applications of Cardiac CT

Historical Evolution of Cardiac CT

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Fundamentals of Cardiac CT

Spatial Resolution

Normal coronary diameters are 2-4 mm

Early CT had collimation of 10 mm

Temporal Resolution

At a heart rate of 60bpm, one cardiac cycle is 1 second (1000ms)

Acquisition time must be fast enough to arrest motion

ECG Gating

Scanner must be synchronized with cardiac cycle

Historical Evolution Current Practice Future Directions

Early CT

Single Detector

Electron Beam


CT Developments

Sequential versus

helical acquisition

Slip ring technology


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Multidetector CT

Early systems were 4 row

Eventual progression to 16 and now most commonly used 64 row


Other CT Developments

Gantry rotation

Early systems had rotation speeds of 1s, now as low as 0.27s

Half acquisition reconstruction

Collimator Thickness

10 mm to as low as 0.5 mm currently

Dual Source

Effectively allows scan to occur twice as quickly


ECG Gating Software and hardware developments allowed synchronization of cardiac rhythm to

scanner

System is able to detect “R” waves, or the peak electric activity of the cardiac cycle

Dynamic measurement of “R-R interval”, or time between beats

General terminology – identify cardiac phase as a percentage of the cardiac cycle

Cycle begins at electrical systole, typically 20-45% is peak systole and 75% is mid diastole


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Early Clinical Applications

Early systems retrospective ECG-gating were applied to evaluate for wall motion abnormalities

Contrast enhancement in the context of acute ischemia

Alternate option to NM stress perfusion imaging

As spatial/temporal resolution improved, CT became increasingly useful in evaluation of coronary arteries


Courtesy of S. Bartel, MD

Current Cardiac CT Technique

Cardiac CT – Patient Selection

Coronary Artery Disease

Pre-procedural Evaluation

TAVR

Pulmonary Vein Ablation

Structural/Congenital Heart Disease

Reduce Cardiac Motion for standard CTA


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Coronary CTA – Coronary Artery Disease

Generally for use in low risk patients

CTA serves as an excellent “rule out” test (high sensitivity) for coronary artery disease

Some limitations on precise characterization of stenoses (slightly

limited specificity)

Invasive Coronary Angiography (i.e. catheter based) remains

gold standard in evaluation of CAD


Cardiac CT – LAMC Protocol

Patient preparation

Standard prep for CT exam

GFR

Contrast allergy – premedicate as needed

Heart rate control

Goal to have heart rate < 60

Use of beta blockers (metoprolol)

PO vs IV


Cardiac CT Protocol (LAMC)

Scanner Parameters

GE – Lightspeed VCT

64 row, collimation 0.625mm

4 lead ECG monitor


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IV Contrast

Visipaque 270 or Omnipaque 300 used

Injection rate – 5 ml/sec

Timing run used to determine optimal scan delay

Inject ~20 ml contrast and scan repeatedly to identify peak in ascending aorta

“Fudge Factor” to account for larger injection ~10s

Nitroglycerin**



Prospective Gating (HR <60)

Sequential Acquisition

kV set to 100 or 120

Fixed mAs, based on pt size

Breath hold – hyperventilation

Preference is to scan in diastole,

when heart is most stationary

Generally center acquisition at 75% of cardiac cycle

“Padding” or over acquisition



Prospective Gating (HR <60)


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Cardiac CT Protocol (LAMC) Retrospective Gating (HR > 60)

kV set to 100 or 120

mAs is variable based on phase of cardiac cycle

Pitch – 0.25

Effective dose typically 13-15 mSv

Continuous helical acquisition allows reconstruction of ALL phases of the cardiac cycle

Can also create dynamic images and perform functional analysis



Retrospective Gating (HR > 60)

With Arrythmia – allows some flexibility on reconstructions (oversampling)



Retrospective Gating (HR > 60)


Courtesy of J. Hsu, MD

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Cardiac CT Radiation Dose

Prospective Gating

DLP ~ 400 mGy-cm

Effective Dose ~ 5-10 mSv

Retrospective Gating

DLP ~ 1000-1500 mGy-cm

Effective Dose ~ 15-25 mSv

For Comparison

Nuclear Medicine Stress ~ 9-

18mSv

Conventional Coronary

Angiogram ~6 mSv


Cardiac CT Protocol

Standard reconstructions performed at scanner

Advanced (3D) workstation used for post-processing


Schoepf et al. AJR. 2007

Cardiac CT – Interpretation

Coronary Artery Disease

Evaluate degree of stenosis

Mild – <50%

Moderate – 50-70%

Severe – >70%

Anomalous coronaries

Stent evaluation

Pre-procedural planning

Measurements as needed for indication

Congenital Heart Disease


Refer for ICA

Courtesy of S. Bartel, MD

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Cardiac CT Interpretation

Normal



Mixed plaque – mild stenosis. No further workup



Coronary Aneurysm


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Calcified Plaques – Nondiagnostic by CT (send to ICA)



Coronary Anomaly – ALCAPA


Future Directions of Cardiac CT

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Development Targets

Refined Patient Selection

Improved Scanning Techniques

Quantitative Data Analysis


Patient Selection

ISCHEMIA trial


Future Directions – Scanning Parameters

Temporal Resolution

Dose Reduction


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Future Directions – Temporal Resolution

320 Row CT

Triple Source


Future Directions – Dose Reduction

Improved detector Efficiency

Reconstruction algorithm (iterative reconstruction)

Ties into improved temporal resolution – enhanced use of

prospective gating


Future Directions – Quantitative Data Anaylsis

Fractional Flow Reserve


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Conclusions

Since early CT, developments in scanner speed, beam width, and

ECG gating have allowed profound progress in ability to evaluate

the heart and coronary arteries.

Current imaging techniques require relatively involved preparation

and expertise to perform and interpret exams

Future directions will facilitate easier acquisition and more precise

quantitative analysis of the heart and coronary arteries.

References

GS Hurlock, H Higashino, T Mochizuki. History of cardiac computed

tomography: single to 320-detector row multislice computed

tomography. Int J Cardiovasc Imaging (2009) 25:31–42

UJ Schoepf, PL Zwerner, G Savino, C Herzog, JM Kerl, P Costello.

Coronary CT Angiography. Radiology: Volume 244: Number 1—July

2007

H Machida, I Tanaka, R Fukui, Y Shen, Y Ishikawa, E Tate, E Ueno.

Current and Novel Imaging Techniques in Coronary CT.

RadioGraphics 2015; 35:991–1010

Questions?

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Current and Evolving Clinical Applications of CT in Heart ... · 2/19/2020 3 Multidetector CT Early...

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