Download Pitfalls

Pitfalls in 16Detector Row CT of
the Coronary Arteries
Presented by Intern 許碩修
Introduction
• Conventional coronary angiography
requires admission and cause discomfort
• Current 16-detector row CT enables
visualization of the coronary arteries by
contrast enhancement
• The pitfalls of CT coronary angiography
are closely related to limiting factors and
postprocessing methods
Techniques
• Retrospective ECG-gated scans with 16detector-row CT (0.42-second rotation
time)
• 12 inner detector rings (standard protocol:
pitch=0.31; HR <50 bpm: pitch=0.29)
• 100 ml of iopamidol (300 or 370 mg/ml of
iodine) followed by 40 ml of saline with
power injector at 4 ml/sec
Techniques (2)
• Triggering scanning on 100-HU
attenuation in the ascending aorta
• Section thickness of 0.75 mm with 0.5-mm
overlap, 18-cm field of view, acquisition
matrix of 512*512
• Isotropic voxel of 0.4*0.4*0.6 mm
Preparation
• HR >65 bpm: 40-60 mg of single oral
metoprolol 1 hour before examination
• Sublingual nitroglycerin (0.3 mg) to dilate
the coronary arteries
• HR <68 bpm: temporal resolution of 210
msec
• HR >68 bpm: multiplanar reformation was
performed, resultant temporal resolution is
105-210 msec
Performance
• Initially, the reformation window starts at
400 msec prior to the next R wave
• If motion artifacts exist, repeat with offset
20 ms toward the beginning and end of
the cardiac cycle
– Until no artifacts or 10 data sets are gained
Requirements
• Consistency of data sets as well as
motion-free images of the heart can be
easily evaluated by MPR
• Various image degradation factors cause
– Nonassessable segments
– Pseudostenosis
Artifacts at Coronary
CT Angiography
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Pulsation
Rhythm disorders
Respiratory issues
Partial volume averaging effect
High-attenuation entities
Inappropriate scan pitch
Contrast material enhancement
Patient body habitus
Pulsation
• Most common and important factors
• Motion-free imaging requires a temporal
resolution of 50 msec
• Less movement during the filling phase is
needed for the least amount of blurring
• The RCA and LCX are closer to the atria
than LAD, thus they are more affected by
atrial contraction
Pulsation (2)
• Multiphase reformation and the selection
of optimal reformation windows are
required for different coronary arteries
• The proportion of diastole depends on the
heart rate
• Nonexistent vascular discontinuity or wall
irregularity may appear
400 msec prior to next R
Apparent section gaps
200 msec prior to next R
Pseudostenosis
Rhythm Disorders
• Reliable imaging only in patients with
normal sinus rhythm
• Slightly different cardiac cycle leads to a
section gap and pseudostenosis
• The association of section gaps and heart
rate increase is recognized
Rhythm Disorders (2)
• Apparent multiple section gaps are called
banding artifacts
• The most frequent causes are arrhythmia,
no breath, and alterations in heart rate
• Long acquisition time is associated with
increased frequency of alteration in heart
rate
• In a patient with Af
Respiratory Issues
• Breath-hold instructions and patient
cooperation are essential
• Banding artifacts due to alterations in
heart rate or by incomplete breath holding
is hard to tell apart
Partial Volume
Averaging Effect
• The assessability of vessel diameter
depends on spatial resolution along the z
axis (greater than 1.5 mm)
• The blooming effect on the coronary
lumen due to calcification or intracoronary
stent
• The plaque attenuation depends on
imaging plane or section thickness
Streak Artifacts from
High-Attenuation Entities
• Streak artifacts are generated by highattenuation entities, high-contrast
interfaces and cardiac motion
• Highly concentrated contrast medium in
the SVC can interfere the RCA
– Decrease with appropriate scan timing and
administration of saline
Streak Artifacts from
High-Attenuation Entities
• Dense and extensive calcification causes
streak artifacts and partial volume
averaging effect
• The artifacts depend largely on the stent
material
– Stent of gold cause the most severe artifacts
Inappropriate Scan
Pitch
• The pitch is limited by patient’s R-R
interval
– Standard is used with HR >50 bpm
– Low pitch is needed to completely cover the
coronary arteries with long R-R interval
• Shortage of data with unpredictable
brachycardia may exist
• Blurred image and pseudostenosis are
found
Contrast Material
Enhancement
• Excellent enhancement of the coronary
arteries and minimal of the coronary veins
by
– Autodetection of contrast material
– Adequate amount and rate of injection
Patient Body Habitus
• Image quality in very obese patients is
poor due to a low signal-to-noise ratio
– A section thickness of 1 mm instead of 0.75
mm is applied
• To maintain the balance, it is necessary to
increase the radiation dose or the section
thickness
Postprocessing Pitfalls
• The potimal setting should be strictly
applied at volume-rendered images
Postprocessing Pitfalls
• Postprocessed images such as VR and
MIP do not show inner lumina
• MPR and curved planar reformation can
demonstrate portions of the inner lumen
• Virtual endoscopy allows evaluation of the
lumina from the inside but cannot provide
quantitative information
Anatomy of the
Coronary Arteries
• Knowledge of the anatomy of the coronary
arteries is required for correct
interpretation
• The left main coronary artery divides into
the LAD and the circumflex artery
• In about 10% of cases, LCX continues as
the posterior descending artery, which is
referred to as left dominant
Anatomy of the
Coronary Arteries
• Myocardial bridges may simulate stenosis
of the proximal LAD artery when images
are reformed during systole
• In rare instances, a coronary artery may
have an anomalous origin and course
Improving the
Diagnostic Accuracy
• Excellent structural consistency and no
motion artifacts
• The reformation window settings and the
effects of the heart rate has been focused
• Most important limiting factors
– Heavy calcification
– Motion artifacts
– A vessel lumen diameter less than 1.5 mm
Conclusion
• The advantages and disadvantages of
each post-processing method should be
clarified
• Familiarity with these common pitfalls,
coupled with the knowledge of normal
anatomy and anatomical variant
Conclusion
• Optimal work flow should be determined
Thanks for Your
Attention!