Transcript CARDIAC MDCT DR RAJESH KF.ppsx

• DR RAJESH K F
• Cardiac CT and CCTA
has emerged as
promising noninvasive
imaging modality for
coronary artery and
cardiac structural and
functional evaluation
Formation of CT image
• Three phase process
• Scanning phase -scan data
• Reconstruction phase processes acquired data
and forms digital
image(pixels)
• Digital to analog
conversion phase - Visible
and displayed analog
image (shades of grayHounsfield units)
Sequential mode
• First scanning mode
• Scan and step
• Prospective triggered
• One complete scan around
body while body is not
moving
Spiral or helical scanning
• Retrospective gating
• Body moved continuously as
x-ray beam scan around
• Higher radiation dose
SDCT
• Single detector row
helical/spiral CT
MDCT
• Electronically acquire
multiple adjacent
sections simultaneously
Full Scan Reconstruction
• Full rotation (3600)
reconstruct one image
Half-scan reconstruction
• Commonly used in cardiac CT
• Data from 1800 sweep
• Temporal resolution- half
gantry rotation time
Multisegment reconstruction
• For multidetector systems
• Use <1800 rotation
Temporal resolution
• Gantry rotation time decreased
• Temporal resolution correspond to half rotation time
• Maximum gantry rotation time - 270 to 330 msec
• Temporal resolution is approximately 83 to 165 msec - halfscan reconstruction techniques
• Image acquisition or reconstruction during periods of limited
cardiac motion (end systole to mid-late diastole)
Spatial resolution
• Decreased slice collimation (thickness)
• Approximately 0.5 mm3
Strengthened X-ray tubes - Reduce image noise
Multislice
• Data in more slices simultaneously
• From 4 to 64 to 320 per rotation
• Decreases overall duration of data acquisition, breath hold
duration and amount of contrast
64-slice scanners
• High temporal and spatial
resolution
• Gantry rotation times of
420 ms or shorter
• Spatial resolution of 0.4
by 0.4 by 0.4 mm
• “state-of-the-art”
equipment for CTA
• Breath hold is 6 to 12 s
256 slice CT
• Spatial and temporal
resolution remain
unchanged
• Approx 0.5-mm collimation
• Increase volume coverage
(number of slices)
• Image heart in single beat
• Less vulnerable to
arrhythmia
Temporal resolution (half-scan
reconstruction)
Spatial resolution
Volume coverage
Breath-hold
4-ROW
16-ROW
64-ROW
320-ROW
250 msec
210 msec
165 msec
175 msec
1.25 mm
0.5-3 cm
30-40 sec
1 mm
1-2 cm
20 sec
0.4 mm
2-4 cm
10 sec
0.4 mm
15 cm
2 sec
Dual-source CT
• Number of slices - 64
• 2 X-ray tubes and detectors
in single gantry at 90°
• One-quarter rotation of
gantry collect data from
180° of projections
• Temporal resolution is twice
of single X-ray tube and
detector
• Reduce motion artifact
Thin-slice cardiac CT
reconstructions
• Displayed in any
imaging plane
Multiplanar imaging
• Oblique planar views
• Images displayed in
orthogonal planes (axial,
coronal, sagittal) or
nonstandard planes
• Analysis of cardiac
chambers
Maximal intensity projection
• Thick-slice projections
• Pixel within slab volume
with highest Hounsfield
number is viewed
• Ability to view more
structures in single planar
view
• Can obscure details when
high-density structures are
present (coronary artery
calcium)
Curved multiplanar
reformations
• Curved structures can be
viewed in planar oblique
multiplanar reformats
• Can be used to evaluate
entire coronary tree in
one view
Volume rendered
reconstructions
• Useful for revealing
general structural
relationships but not for
viewing details of
coronary anatomy
• Non-contrast study
• Refine clinically predicted
risk of CHD beyond that
predicted by standard
cardiac risk factors
• Used in asymptomatic
patients
• Coronary calcium Present
in direct proportion to
extent of atherosclerosis
• Minority (20%) of plaque
is calcified
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3 mm non overlapping thick tomographic slices
Average about 50–60 slices
From coronary artery ostia to inferior wall of heart
Calcium score of every calcification in each coronary
artery for all of tomographic slices is summed
CALCIUM VOLUME SCORING
Area = 8 mm2
Peak CT = 290
Score = 8 x 2 = 16
Area = 15 mm2
Peak CT = 450
Score = 15 x 4 = 60
AGATSTON SCORE =
Sum
Hn x-factor
(Agatston Scoring)
130-199
1
200-299
2
300-399
3
>400
4
4 calcium score categories
0
none
1–99
mild
100–400
moderate
>400
severe
Calcium score correlates directly with risk of events
and likelihood of obstructive CAD
Interscan variability of 10% to 20%
• Coronary calcium
presence and extent are
dependent on age,
gender, ethnicity, and
standard cardiac risk
factors
• Calcium scores are
higher for age and male
gender among whites
• Data from 13 studies
(75,000 patients) during
4 years - calcium score
of 0 is associated with a
very high event-free
probability (99.9% per
year)
*
*p<0.001
*
*
Shaw et al. Radiology 2003; 228:826-833
GLOBAL CHD
RISK ESTIMATE
SCORE
Noncontrast CT for coronary calcium score
Low risk with a
family history of A
premature CHD
Noncontrast CT—coronary calcium score
Low
I
Noncontrast CT—coronary calcium score
Intermediate
A
Noncontrast CT—coronary calcium score
High
U
• Helical scan
• Provide CT data from
systole and diastole
• Can be displayed in
cine-loop format
• Estimation of RVEF, LVEF,
volumes and RWMA
• EF highly accurate
• Myocardial morphology
- wall thinning,
calcification or fatty
replacement (negative
HU densities)
• Atrial morphology and
volume
Evaluation of LV function in acute MI or HF with
inadequate images from other noninvasive methods
A
Quantitative evaluation of RV function
A
Assessment of RV morphology in suspected ARVD
A
• Anatomic evaluation of
cardiac valves and their
motion
• Both native and prosthetic
• Lack of physiologic valve
flow evaluation
• Prosthetic valve
malfunction- size mismatch,
tissue ingrowth, and valve
thrombosis
• Severe AR- malcoaptation
of leaflets >0.75 cm2
• AS- extent of valve
calcification and planimetry
• Planimetry equalent to
other invasive and
noninvasive methods
• Aortic valve calcification is
directly related to valve
area and quantitated by
area-density methods
• Less information concerning
tissue type than CMR
• Lipomas-low CT numbers
(< 50 HU)
• Cysts – water like density
(0 to 10 HU)
• Intracardiac thrombi – (20 to
90 HU)
• Density values overlap with
myocardium
• Identify thrombi in LAA
• Poor enhancement of LAAfalse-positive result common
• Embedded in epicardial
and pericardial fat-can
be delineated in CT
• Normal thickness-1to 2mm
• Can clearly delineate
pericardial calcification
Characterization of native cardiac valves or prosthetic valves with clinically
significant valvular dysfunction when other noninvasive methods are
inadequate
A
Evaluation of cardiac mass (suspected tumor or thrombus) with inadequate
images from other noninvasive methods
A
Evaluation of pericardial anatomy
A
Evaluation of pulmonary vein anatomy prior to RFA for AF
A
Noninvasive coronary vein mapping prior to biventricular pacemaker
A
• Visualization of coronary
arteries and lumen
• Excellent tool to investigate
coronary artery anomalies
Problems
• Rapid motion
• Small dimensions of
coronary arteries
• Temporal and spatial
resolution of CT
Lower heart rate to 60 beats/min - Oral or intravenous BBs
• Metoprolol 25 to 100 mg orally 1 hour before or IV 5 mg rpt doses
Dilate coronary arteries
• Sublingual nitrates immediately before scanning
• Nitroglycerin 400 to 800 Microgm
Breath hold of 6 to 20 s
• Depend on scanner generation and dimensions of heart
• 50 to 120 ml of contrast IV
• 3 to 15 mSv, depending
on scan protocol
• ECG-correlated tube
current modulation
• Reduction of tube current
in systole
• Can reduce radiation
exposure by 30% to
50%
• Transaxial image
• 2D image reconstruction
• Maximum intensity
projections
• Facilitate data
interpretation
• Only maximal density
values at each point in
3-D volume are
displayed
• 2D image reconstruction
• Curved multiplanar
reconstruction
• Evaluate entire coronary
tree in one view
• 3 Dimensional display
• Visually pleasing
• Rarely helpful to
evaluate data
Motion artifact
• Irregular and fast HR
• Respiration
• Limit temporal and
spatial resolution
• Blurr contours of
coronaries
RCA - most frequently
affected
Partial volume effect
• e.g., metal, bone ,
calcifications
• Appear bright on image
• Lead to overestimation of
dimensions of high-intensity
objects
• Accuracy for detection of
coronary stenoses is lower
Streaks and low-density
artifacts
• Adjacent to regions of
very high CT density
• e.g., metal or calcium
64-row CTA
• Overall accuracy
• Sensitivity of 87% to 99%
• Specificity of 93% to 96%
• NPV -93 to 100%
• ~4% uninterpretable
• Specificity reduced in
calcium scores > 400 to
1000 or obesity (excess
image noise)
• Best for ostial and first
centimeter lesions
Most studies are limited by selection of patients optimized for cardiac CT and
analysis involves only more proximal coronary segments down to 1.5 mm
• Compared with grading by
CAG, CT CAG stenosis
severity tends to be worse
and correlation is 0.5-0.6
• Correlates very well with
IVUS (better visualization
of arterial wall)
• >50% stenosis on cardiac
CT has 30% to 50%
likelihood of demonstrable
ischemia on MPI
• Identification of
obstructive CAD did not
successfully identify
individuals with
abnormal MPS
• Measures of perpatient
coronary artery plaque
burden, proximity, and
location predictive of
identifying individuals
with abnormal MPS
• Rapid (>80 bpm) and
irregular HR
• High calcium scores (>8001000)
• Stents
• Contrast requirement
• Small vessels, distal vessels
(<1.5 mm) and collaterals
• Obese
• Radiation exposure
Non-Acute Symptoms Possibly Representing an Ischemic Equivalent
1. ECG interpretable and able to exercise
Low
2. ECG interpretable and able to exercise
Intermediate A
3. ECG interpretable and able to exercise
High
4. ECG uninterpretable or unable to exercise Low
U
I
A
5. ECG uninterpretable or unable to exercise Intermediate A
6. ECG uninterpretable or unable to exercise High
U
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2%-6% of patients are erroneously discharged with missed MI
CCTA useful in this patient subgroup
Highlighting the NPV of CCTA
A successful triage tool that may allow safe early discharge of
low-risk patients
Normal ECG and cardiac biomarkers
Normal ECG and cardiac biomarkers
ECG uninterpretable
ECG uninterpretable
Low/Intermediate
Nondiagnostic ECG or equivocal cardiac biomarkers
Low/Intermediate
Nondiagnostic ECG or equivocal cardiac biomarkers
High
High
Low/Intermediate
High
Acute chest pain of uncertain cause (differential diagnosis includes
pulmonary embolism, aortic dissection, and acute coronary syndrome [triple
rule-out])
A
U
A
U
A
U
U
ECG Exercise Testing
Exercise testing and Duke Treadmill Score, intermediate-risk A
Normal exercise test with continued symptoms
A
Stress Imaging Procedures
Discordant ECG exercise and imaging results
A
Stress imaging results: equivocal
A
Diagnostic Impact of Coronary Calcium in Symptomatic Patients
Coronary calcium score <100
A
Coronary calcium score 100-400
A
Coronary calcium score >401-1000
U
• Sensitivity and specificity nearly 100%
• Large size and limited
mobility of grafts
• Limitation in native
coronary artery evaluation
(metallic clips and calcium)
• Cardiac structures
adjacent or adherent to
sternum and grafts cross
midline can be seen
Symptomatic (Ischemic Equivalent)
Evaluation of graft patency after coronary bypass surgery
Asymptomatic
Localization of grafts and retrosternal anatomy prior to
reoperative chest or cardiac surgery
A
A
• Image artifact limits
application
• Accuracy of 90% in stents
>3 mm
• Small stents are difficult to
evaluate
• Dependent on stent design
• Optimization of
reconstruction techniques
(sharp kernel) and display
characteristics (wide
display window)