State-of-the-art Cardiac CT of the coronary arteries

Cardiac CT
E. R. Ranschaert
Radiologist

Arab Health Congress, Jan 28-31, 2013

Introduction

 Technical aspects

 Scanning procedure

 Indications for c-CTA

 Clinical cases

 64 slice

 dual source CT

Copyright E. R. Ranschaert

Coronary CTA

 Main purpose: morphology

 Detection and analysis of
coronary artery disease

 Depict anatomy of coronary
vasculature

 Possible to obtain functional
information in same scan

 contractility of myocardium

 valve morphology and function

 “viability” of myocardium
(perfusion-CT)


Multislice CT - MDCT

 Evolution of Cardiac CT is
strongly linked to technical
improvements in CT-
scanners

 Preferably 64-slice scanner
or more

 Our current machine:
dual source CT 2x64 slice
(Somatom Definition Flash)

 Other vendors: 256-slice or
higher


Volume coverage – helical scan
 Time to cover heart decreases with larger detector arrays,
shorter tube rotation times and faster table movement

4 x 1 mm slice 16 x 1mm slices 64 x 0.5 mm slices
4 mm 16 mm 32 mm

~48 sec ~12 sec ~6 sec
Copyright E. R. Ranschaert 0.5 s rotation, 0.33 pitch
Courtesy of Sue Edyvean, ImPACT – www.impactscan.org

“Old” generation scanners
16-slice 64-slice

Images used with permission of James Carr, MD

Newer generation scanners
Complete coverage High pitch
Toshiba Acquilion Siemens Definition Flash
Seq 256-slice, spiral 64-slice 2x 64 slice

single rotation fast pitch, no gaps

Copyright E. R. Ranschaert Courtesy of Sue Edyvean, ImPACT – www.impactscan.org

Multi-sector scanning
Min. 2 sectors needed per image

Graphics used with permission of Sue Edyvean, ImPACT – www.impactscan.org

Multi-sector scanning

GE Philips Siemens Siemens Toshiba
1 tube 2 tubes
# sectors 1,2,4 up to 5 1 or 2 1 or 2 up to 5

Graphics used with permission of Sue Edyvean, ImPACT – www.impactscan.org

Dual source CT

(0,285 s rotation for entire heart)

Graphics used with permission of Sue Edyvean, ImPACT – www.impactscan.org Copyright E. R. Ranschaert

FLASH-CT
Volume-rendered MPR - normal LAD


Patient Preparation

 General CT-preparation:
 Renal function, hydration, stop Metformin if
GFR<60, premedication for iodine allergy

 Specific cardiac-CT preparation:
 Information sheet specifically for cardiac CT

 Beta-blockers: P.O. (in advance)

 Other premedication if needed


Day of scanning
 3-4 h in advance: no meal, no coffee, no tea

 2h in advance 25-100 mg metoprolol
P.O. (selective β1 receptor blocker)

 Fine tuning HR with IV injection, 5-20 mg extra
 Selection of scan protocol depending on bpm
variability
 For Flash: ≤65 bpm and regular HR needed


ECG monitoring on scan
 ECG monitoring is used to “freeze” cardiac motion

 Images made during phase of least cardiac motion

 Phase is given as % of R-R interval


Scanning
 Breath hold on ¾ of full inspiration (prevents
Valsalva manoeuvre)
 Breathing instructions are practiced with
patient before scanning
 Nitroglycerine spray immediately before
scanning 1 puff
 Contrast (high iodine concentration) is injected
at 5-6 ml/sec


Stable HR needed
 Motion needs to be repeatable – regular heart rate
 reduce potential for mis-registration
 applies for both axial and helical

iiiii
iiiii
iiiii
ECG


Misregistration

Stairstep artefacts Copyright E. R. Ranschaert

Calcium scoring
 First calcium score is
determined

 low dose non-enhanced
triggered scan

 Semi-automated
calculation of score

 Decision to make c-CTA
based upon score and
age

 Score 0 >60j: no cCTA

 >600: no cCTA


Selection CTA scan protocol

 3 acquisition modes with ECG synchronisation

1. Retrospective gating

2. Prospective triggering = sequential/axial =
“adaptive sequence” (Siemens)

3. FLASH = prospective triggering spiral scan with
very high pitch


1. Retrospective gating
 Spiral scan technique

 Small overlapping pitch ≅ 0,2

 Heart scanned in all phases

 Breath hold = 7-12 sec

 Retrospective selection of
best phase for
reconstruction/reviewing

 Functional information

 10-12 mSv


Cardiac CT – ECG phases
 Optimal phase for reconstruction for CTA
 diastole @ ~ 70 %

Optimal reconstruction phase

R R

70% R-R

Eg. 50 60 70 80

Courtesy of Sue Edyvean, ImPACT –R. Ranschaert
Copyright E. www.impactscan.org

2. Prospective triggering
 ACS: Adaptive Cardio Sequence

 Sequential technique

 ECG-signal is used to trigger scanning
(R-wave)

 “Padding” opens scan pulse
(30-80% RR)

 With “padding” more phases are
available for review (steps of 1 – 20%)

 Dose reduction up to 87% compared
with retrospective scanning (2,5 - 3 mSv)

 Usable in patients with slightly irregular
heart beat
Courtesy of Siemens: Thomas Flohr, Cardiac CT Acquisition modes


Triggering
 R wave recognised - scan triggered

Radiation on

(and attenuation
data acquired)


Management of extrasystoles
 Selection Low / Medium / High protocol depends on
HR (60-85 bpm)
 ACS makes analysis of ECG, ectopic heart beats are
detected

 Start of scan is prospectively based upon last 3 cycles

 Scan is omitted & delayed when extrasystole is
detected before scan

 Scan is repeated when extrasystole occurs during or
shortly after scan

 Flex padding uses extended acquisition window: gives
more flexibility to find optimal reconstruction phase



Padding

„padding‟ for
CTA
Radiation on

(and attenuation
data acquired)

480° rotation


Padding

„padding‟ for
CTA
Radiation on

(and attenuation
data acquired) 70

Required data
for image
recon.


Padding
 Axial scanning with „padding‟
 More flexibility with reconstructed phase position

„padding‟ for
CTA
Radiation on

(and attenuation
data acquired). 60

Required data
for image
recon.


Padding
 Axial scanning with „padding‟
 More flexibility with reconstructed phase position

„padding‟ for
CTA
Radiation on

(and attenuation
data acquired).

Required data
for image
recon.

3. Flash – single beat, high pitch
• 2 Sectors of data acquired simultaneously in ¼ rotation = 75 ms
• Whole heart in 3¼ rotations = 0,28 sec
• No misregistration, no stair-step artefacts: 1 shot!

Copyright E. R. Ranschaert Courtesy Siemens

Which protocol to use?
 RETROSPECTIVE:
 Only with patients that are not suited for prospective
scanning due to arythmia, high HR or both
 If functional imaging is needed (LVA)

 PROSPECTIVE:
 Stable and low HR
 Slight arythmia
 With ACS: 65-85 bpm
 Low – medium – high protocol
 Also LVA possible with adaptive sequence (padding)

 Use Flash whenever possible!
SCCT guidelines on radiation dose and dose-optimization strategies in cardiovascular CT,
Halliburton SS et al., J Cardiovasc Computed Tomogr (2011)5, 198-224

Indications for c-CTA

 Calcium scoring
 Risk stratification
 Decisive before CTA examination

 Coronary CTA
 Anatomy of coronary vessels (CAG difficult)
 CAD (low to intermediate risk)
 Stent viability
 Anatomy and patency of grafts after CABG

 Functional analysis


Calcium scoring

 “Gatekeeper” for further cardiac
examination if pre-test probability is low and
EST is not possible

 Added value in risk stratification (re-
stratification of medium risk)
 With men and female >60y
score = 0 is very reassuring (high NPV)


Assessment of stenoses

 Visual assessment

 Significant
(obstructing) is > 50%

 Non-significant or non-
obstructive < 50%

 Resolution vs. CAG:
20% margin is taken Non-obstructing stenosis
Significant stenosis
into account


Limitations of cCTA

Irregular HR
obesity
stents < 3 mm
Calcium and stents:
“blooming” artefacts lower
specificity of cCTA



Blooming Artefact
 Blooming artefact – calcium/stent obscures vessel
 Improvement with better spatial resolution

Improved spatial
resolution
and display
(recon alg., fov)

49


Diagnostic accuracy of cCTA

 CAG is gold standard
cCTA
 Ideally patients with
stable HR +
stable AP complaints Sens 96-99%
or atypical chest pain

 Very useful to exclude
Spec 88-91%

significant CAD: high
NPV NPV >90%

Low to intermediate risk patiënts

Anatomy
Left main stem

RCA

AM

PDA Cx

Diag branch

LAD


Functional assessment


Case 1

 F, 43y

 Atypical precordial
complaints

 EST-test negative


Case 2

 F, 68y

 Chest pain

 Pain after exercise
stress testing, ECG
normal


cCTA: extensive CAD with short occlusion RCA

Advise to perform CAG


Case 3

 M, 33y

 SEH left thoracic pain
irradiation to left arm

 CAG: no significant
stenoses demonstrated,
“catheter spasm”

 In history probably limited
myocardial infarction

 cCTA performed 3m later


yright E. R. Ranschaert

Non-stenosing non-calcified plaque in prox. circumflex artery

Case 4

 M, 43j

 Chest pain, arm pain while
painting during 30 min

 Normal EST,
ECG normal

 cCTA


Case 4

 Chronically
occluded RCA

 ectatic coronary
system


RCA

Reinjection via left system


Non-calcified plaque
“ectatic” LAD


Case 5

 Woman, 1967

 Atypical precordial
pain PA
Ao
 Cycling test negative

 Low risk

PA
RCA

Ao

Anomalous RCA

 Anomalous RCA arising
from left sinus of valsalva

AA PA  Most common pathway for
ectopic RCA
RCA
 Associated with sudden
cardiac death in 30% of pts

 Dilatation of Ao during
RCA
PA excercise comprises RCA,
may lead to AMI
inter-arterial course of RCA
Ao


Ao
RCA PA


Anatomic variant

 Left CA main branch: origin
posterior on AA

 from non-coronary sinus of
Valsalva

 Retro-aortic course

 Usually no clinical
relevance
LA
D

Cx


Case 2 flash

 Male, 56 y

 Chest pain (AP-complaints)

 ECG doubtful

 Hypertension

 High cholesterol


Case 3


Ostial aneurysm RCA


Post CABG

 64-slice scan

 3 venous grafts Occluded

 Patency grafts?

 Only graft to RCA open

Open


Origin of LAD graft not Start scan high
visualised enough!

Cx graft


Post-CABG

 Male, 81y

 CAG was performed:

 Graft from AO to LAD could not be visualised

 prox. occlusion?


Cx graft: patent RCA graft: occluded
proximally


Case 4

 78y-old female patient

 Previous CABG

 Unstable AP

 Dialysis patient

 CAG unsuccessful: LIMA not visualised

 Dual source CT, retrospective scanning


Findings
LIMA 3D LIMA 2D


Findings case 4
LIMA – LAD anastomosis Distal LAD

Stenosis


Case 5
History Calcium scoring
 Female, 1963

 Referred by GP for atypical
chest pain, dyspnea with
effort

 Bicycle ergometry: not
conclusive

 ECG mild abnormalities


Case 6
cCTA Flash mode
MIP


Case 6
LAD LAD


Case 6 – stent evaluation
Pre-stenting Post-stenting


Case 6: stent evaluation
Stent LAD Diagonal branch


Case 7

 Female, 51 y

 Dyspnoea with effort,
fatigue, no chest pain

 FA: father sudden death at
55y, probably AMI

 ECG normal


Case 7
RCA

Non-calcified stenosis 70%

The End
Thank you!

http://nl.linkedin.com/in/eranschaert/
e.ranschaert@jbz.nl

State-of-the-art Cardiac CT of the coronary arteries

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State-of-the-art Cardiac CT of the coronary arteries