Cardiac Imaging Overview
Matthew Bentz, MD
OHSU Diagnostic Radiology
Assistant Professor
2016
Leading causes of death, 2011 USA
0
100,000
200,000
300,000
400,000
500,000
600,000
700,000
Heart Disease
Cancer
Chronic lower
respiratory disease
Stroke
Accidents
Alzheimer's
Diabetes
Influenze & pneumonia
Renal disease
Suicide
Homicide
CDC National Vital Statistics Report 2011
History
• In 1698, Chirac ligated the coronary of a dog
and noted that soon after the heart ceased to
beat*
• In the late 1890’s, Porter in London studied
changes in systolic & diastolic pressures after
coronary ligation
*Chirac P: De Motu Cordis, Adversaria Analytica, 1698, p. 121
** Porter T: On the results of ligation of the coronary arteries. J Physiol (London) 15: 121, 1895
History
• In 1912, Herrick reported that coronary
occlusion led to myocardial infarction†
• Tenant & Wiggers began the modern era of
study regarding the pathophysiology of
myocardial ischemia, beginning in the 1930’s‡
† Herrick JB: Clinical features of sudden obstruction of the coronary arteries. JAMA 59: 2015, 1912
‡ Tennant T, Wiggers CJ: Effect of coronary occlusion on myocardial contraction. Am J Physiol 112: 351, 1935
Objectives
• Discuss why we care about ionizing radiation and
describe radiation related risks
• Discuss the “ALARA” principle
• Be able to discuss the common cardiac CT studies
that we perform here at OHSU
• Learn or review the common CT artifacts and
how to fix them
Cardiac Imaging Modalities
• Electrocardiogram (ECG/EKG)
• Echocardiography
• Cardiac MRI
• Nuclear medicine
• Cardiac CT
Cardiac Imaging Modalities
• Cardiac CT
• Electrocardiogram (ECG/EKG)
• Echocardiography
• Cardiac MRI
• Nuclear medicine
Cardiac CT Studies
• Calcium Scoring
• Coronary CTA
• Pulmonary Vein Mapping
• Aorta Imaging and TAVR
• Congenital Cardiac CT
Ionizing radiation
Ionizing radiation
• CT
• Fluoroscopy/Radiography
• Nuclear medicine
No ionizing radiation
• MRI
• Ultrasound
Effects of Ionizing Radiation
• Deterministic – Increasing doses of
radiation will cause certain effects
• Approximately 2 Gray will cause red skin
• More radiation will worsen the effects
• Stochastic – Probability related
• 2 Gray of radiation may cause cancer, it may not
• ↑ radiation = ↑ cancer probability
• ↑ radiation ≠ ↑ cancer severity
• If a pt. gets an ionizing radiation related cancer, it
may take decades to appear
ALARA
• As Low As Reasonably Achievable
– Ionizing radiation has harmful side effects
– More radiation is worse
– Use as little as possible
Controversy!
• Hormesis?
– Kerala, India has high
natural background
radiation (estimated at
80X London), but a 10
year study of almost 70K
residents did NOT show
increased cancer
DLP
• Dose Length Product
– A number given by the CT scanner for each scan
– Related to radiation doses calculated from
phantoms
– For cardiac studies, multiplying this number by
0.025 (2.5%) gives a rough estimate of dose in
milliSieverts
Coronary Calcium Scoring
• A non-contrast, gated Cardiac CT to look at the amount
of calcium in the coronary arteries
• Should be done in normal healthy patients, or prior to
a coronary CTA
– If the calcium score is high enough (>1000?), the coronary
CTA will be suboptimal and may not be worth doing
Coronary Calcium Scoring
• The result is a number, called the “Agatston
Score.”
– The score is a combination of the density (>130 HU) of
the calcifications and the size of the calcifications
• We also report a percentile score, based on the
patient’s age and gender
Coronary Calcium Scoring
• No or minimal (<10) is a good negative predictor
• Mild (11-100) and Moderate (101-400) less useful
• Extensive (>400) is high risk
The American Journal of Cardiology Vol. 87 June 15, 2001
Calcium Scoring
Calcium Scoring
Dose
• Dose should be low
• Estimates are in the range of 1 mSv
– DLP <100
Cardiac Gating
Prospective
• Lower Dose
Retrospective
• Higher Dose
• Function cannot be assessed • Function can be assessed
• One shot – images may be
suboptimal
• Multiple series, multiple
chances to get motion-free,
high quality images
Coronary CTA through the ED
• Used in low to intermediate risk patients
– 1st set of cardiac enzymes should be back and should
be negative
– Negative or indeterminate ECG
• This should NOT be used in high risk or positive
patients
– Delays definitive treatment
– Places high risk and/or actively infarcting patients in CT
Coronary CTA through the ED
– Exclusion criteria
• Absolute
–
–
–
–
Severe allergy to iodinated contrast
Advanced renal insufficiency
Inability to lie flat
A patient who is actively having a heart attack
Coronary CTA through the ED
– Exclusion criteria
• Relative
– Pregnancy
– Irregular heart beat
– Inability to breath hold for ~10 seconds
– Mild renal insufficiency
– Contraindications to β-blockers (Bronchospasm)
– Contraindications to Nitroglycerin
– Patient weight >350-400 lbs
– Known high calcium score (>400? >1000?)
– Recent (2 years?) normal coronary angiogram
Coronary CTA through the ED
– Exclusion criteria
• Relative
– Contraindications to
Nitroglycerin include
the recent use of Cialis,
Viagra, or other
phosphodiesterase-5
inhibitors
Coronary CTA through the ED
– 5.4/10 on IMDB
– “A raucous comedy
about an unlucky hipster
who accidentally takes
two Erectile Dysfunction
pills and goes through a
day of misadventures.”
Digression
Epimedium grandiflorum, AKA
barrenwort, bishop's hat, fairy
wings, horny goat weed, rowdy
lamb herb, randy beef
grass and yin yang huo
Xanthoparmelia, AKA
Rock Shield Lichen
In the ED, before the CTA is ordered
– Patient has chest pain
– H&P done
– ECG negative or indeterminate
– 1st set of cardiac enzymes negative
– Screening for contraindications done
Next steps after the CTA is ordered
– Pt can have water, otherwise NPO until after the CT
– Check the patient’s heart rate
• Above ~65, we give IV metoprolol
– In the future, and in other places, the ED gives the patient oral
metroprolol
– A few minutes before the scan, we give 1.5 tablets (600 µg)
of nitroglycerin
– Important that the patient is coached, and then performs
an adequate breath hold
– ECG Gated CTA of the coronary arteries is performed
What we do with the images
– We’re looking for severe
or “high grade” stenoses
• A narrowing greater than
50% in the left main
coronary
• A narrowing greater than
70% in the other vessels
– This is an example of a
high grade stenosis ->
Raff, GL et al. “SCCT Guidelines for the Interpretation and Reporting of Coronary CTA.
Society of Cardiovascular Computed Tomography 2009.
Coronary CTA - Normal
Coronary CTA
• A more subtle
abnormal case
• Moderate
narrowing of the
mid vessel (LAD)
• Artifacts make
cases like these very
difficult
Dose
• Beta blockers slow heart rate, letting us do a
prospective study
• DLP usually in the 100’s to 200’s
– Less if calcium scoring not done before CTA
Pulmonary Vein Mapping
• Atrial fibrillation is common
– An irregular and rapid heart rhythm
• It increases the risk of stroke, and can lead to
heart failure
• Often, the cause of the A fib is in the
pulmonary veins. Pulmonary vein ablation
can cure the patient
Pulmonary Vein Mapping
• Our goal with these CTs is:
– To define the anatomy of the
pulmonary veins
– To describe the morphology
of the left atrial appendage,
and report if a clot is present
– Secondarily look at the
coronary arteries
Pulmonary Vein Mapping
• CT with contrast
• Gated, but no
medication given
• Timed for opacification
of the pulmonary veins
and left atrial
appendage
Pulmonary Vein Mapping
• Left atrial appendage filling defect
– May represent thrombus or slow flow
Dose
• Small volume of
coverage
• DLP usually between
100-200
TAVR
• TAVR= Trans-catheter Aortic Valve Replacement
• Currently, this technique is used for patients
who are too sick for a surgical AVR
• Will likely become much more commonly used
in the future
TAVR
• Gated, contrast enhanced CT of the heart
– Measure of the aortic valve, to determine the
necessary size prosthetic valve
• Includes CT of the entire aorta and pelvic
vessels, during the aortic phase
– Aorta and iliac arteries are measured, to ensure
that they are big enough for the catheters to be
placed
TAVR Dose
• This will be the highest
dose cardiac study
– Retrospective studies are
higher dose than
prospective, includes
entire Chest, Abd, Pel
– Not uncommon to have
a DLP in the 3000s
CTA for TAVR Planning
Scan Mode
Collimation
kVp
mA
HP
Rotation
Time
Scan
Range
Volume
0.5mm x 280
100
300
N/A
0.35 s
Ultra-Helical
0.5mm x 80
100
SUREExposure
111
0.35 s
*AAPM Report 96
Dose
Reduction
CTDIvol
DLP
Effective
Dose
k Factor
140 mm
2.8 mGy
38.6 mGy•cm
0.54 mSv
0.014*
633 mm
5.1 mGy
355.5 mGy•cm
5.1 mSv
0.0145*
Congenital Cardiac CT
• Echocardiogram and cardiac MRI are the main
tools used in pediatric cardiac imaging
– No ionizing radiation
• CT is also commonly used because it has excellent
spatial resolution
• Congenital “cardiac” imaging is a broad category
– Includes venous, cardiac, pulmonary arterial,
pulmonary venous, aortic and coronary arterial
abnormalities
Congenital Cardiac CT
• Prospective gating whenever possible
– Patients are young and will hopefully live for a long time.
– Lowest possible doses to ↓ the long term radiation risk
• For very young/small patients, the study may require a
hand injection
• Unlike MRI (which takes minutes-hours), we can do
many of these without sedation because they are so
fast
– Sedation usually needed for pts between about 6 weeks
and 8 years old
Example
Approx 0.8 mSv
Dose
• Hopefully, and usually, our lowest dose cardiac
scans, but has the most variability
– Includes newborns through adult-sized teenagers
• Not uncommon to be <1 mSv in infants
– DLP often <100
– Above a DLP of 400 is unexpected
Cardiac CT Studies
• Calcium Scoring
• Coronary CTA
• Pulmonary Vein Mapping
• Aorta Imaging and TAVR
• Congenital Cardiac CT
ECG Gating
Retrospective
Prospective
or
Name the artifact
Kroft, et al. AJR 2007
Stairstep Artifact (AKA Stepladder)
• Due to motion
occurring
between
acquisitions
and/or
heartbeats
– Cardiac motion,
respiration, or
patient motion
Which is artifact?
AJR 2007
Stair step Artifact
• Solution:
– Retrospective scan or ↑ scan window (A)
• A region with no motion can be selected
– Reconstruct data from multiple cardiac cycles (B)
• Careful! This doubles or triples the patient dose ↓
Stair step Artifact
• Solution:
– Think about what you’re imaging
• If the question is aorta instead of heart, make sure NOT to place
the stair step over the ascending aorta
– Change location of the window ↓
• 40% versus 75% may decrease cardiac motion
Kroft, et al. AJR 2007
Stair step Artifact
• CT Scanner Upgrade Solution:
– ↓ scan time (make the blue box smaller)
• ↓ gantry rotation time
• ↑ number of sources (Dual Source CT)
CT Detector Evolution
Single Rotation
320 detector row CT coverage
Single Rotation
160 detector row CT coverage
Single Rotation
64 detector row CT coverage
4 cm
8 cm
16 cm
Mimics
Kroft, et al. AJR 2007
Stair step artifact
Kroft, et al. AJR 2007
Curved reformat
artifact
Kroft, et al. AJR 2007
Next artifact
Photon Starvation Artifact
• Dose too low for the
patient
– Low dose or large
patient
0.1 mm
• Increase mAs
– Increase kVp
• Increased slice
thickness helps, but
creates other artifact ->
Modica, et al. Radiographics 2011
10 mm
Next artifact
Beat Rejection Artifact
• Toshiba scanner
• Can be manually
fixed
Next artifact
Metal Density Artifacts
• Beam-hardening,
blooming, and
streaking
• Blooming is
expected if
Calcium is present
– This is why we do a
Calcium Scoring CT
prior to a coronary
CTA
Reducing Metal Density Artifacts
• Demonstrating
calcifications is
important clinical
information
• However, the calcs
cause artifact
– This artifact can
interfere with the
evaluation of a
luminal stenosis
Metal Density Artifacts
• Correct filters
• Correct windows
• Saline flush
• Dual source CT
Metal Density Artifacts
• Correct filters
• Correct windows
• Saline flush
• Dual source CT
Other artifact & technical issues
• Incomplete coverage ->
• Poor opacification of
the vessel lumen
– Extravasation, timing,
Valsalva, etc.
– Ex. Extravasation ½ way
into injection ->
Questions?
Objectives
• Discuss why we care about ionizing radiation
and describe radiation related risks
– Ionizing radiation has predictable risks, like burns,
and probability related risks like cancer
Objectives
• Discuss the “ALARA” principle
– Because ionizing radiation has risks, we apply the
principle “As Low As Reasonably Achievable.”
– That is, ise as little radiation as possible to answer
the clinical question
Objectives
• Be able to discuss the common cardiac CT
studies that we perform here at OHSU
– Calcium Scoring CT
– Coronary CTA
– Pulmonary Vein Mapping CT
– Aorta CTA and TAVR Planning CT
– Congenital Cardiac CT
Objectives
• Learn or review the common CT artifacts and
how to fix them
– Stair step and motion artifact
– Metal density and beam hardening artifact
– Beat rejection artifact (Toshiba)
Objectives
• Discuss why we care about ionizing radiation and
describe radiation related risks
• Discuss the “ALARA” principle
• Be able to discuss the common cardiac CT studies
that we perform here at OHSU
• Learn or review the common CT artifacts and
how to fix them
References
• Kroft LJM, et al. “Artifacts in ECGSynchronized MDCT Coronary Angiography.
American Journal of Roentgenology 2007; 189:
581-591.
• Choi HS, et al. “Pitfalls, Artifacts, and
Remedies in Multi-Detector Row CT Coronary
Angiography.” Radiographics 2004; 24 (3):
787-800.
References
• Otton et al. “Defining the mid-diastolic
imaging period for cardiac CT – lessons from
tissue Doppler echocardiography.” BMC
Medical Imaging 2013:13(5).
• Modica M, et al. “The Obese Emergency
Patient: Imaging Challenges and Solutions.”
Radiographics 2011; 31:811-823.