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- 100 kV imaging
Advantages:
- 100 kV imaging gives large dose reductions (-45%)
- Improves the enhancement of vessels (greater iodine absorption) - Disadvantages:
- Noisier images in large patients due to reduced penetration (don’t use if BMI >30, weight > 190 lbs)
- Not recommended for heavily calcified vessels or stents - Acute chest pain and Cardiac CTA
- Coronary CT angiography (CCTA) has a very high negative predictive value (>90%)
- Ideal for ruling out disease in patients with intermediate or low probability of CAD that you just don’t feel comfortable sending home
- CCTA results in earlier discharge from the ED and may save money over other treatment strategies
- “ Another advantage of using coronary CTA over MPI in the emergency department setting is that coronary CTA can of course, reveal other causes of acute chest pain, such as aortic dissection, pulmonary embolism, pneumothorax, pericardial or pleural disease, tumors, and others.”
The Lack of Growth in Use of Coronary CT Angiography: Is It Being Appropriately Used?
Levin DC et al.
AJR 2011; 196:862-867 - “ The evidence from the literature review suggests that both invasive coronary angiography and myocardial perfusion imaging (MPI) may be overutilized, whereas coronary CTA is probably underutilized.”
The Lack of Growth in Use of Coronary CT Angiography: Is It Being Appropriately Used?
Levin DC et al.
AJR 2011; 196:862-867 - Limitations related to patient specific factors
- Obesity
- Patient motion or poor breathing technique
- Poor venous access - Limitations related to contrast
- Poor injection will limit study quality
- Test bolus or bolus tracking works well as long as it is used correctly - Limited Temporal Resolution
- Limited spatial resolution (150-180 msec) requires a low heart rate (60 or less)
- Beta blockade is critical for patient performance
- Retrospective gating should be used wih high heart rates or with arrthymias - What factors may make a CCTA nodiagnostic?
- Spatial resolution
- Temporal resolution
- Contrast enhancement
- Other patient specific factors "This review discusses the identification and resolution of the most commonly encountered artifacts that may cause a CCTA to be nodiagnostic, including aspects to (1) spatial resolution, (2) temporal resolution, (3) contrast enhancement, (4) other patient specific factors ."
What makes a coronary CT angiogram nondiagnostic?
Min JK, Lin FY
J Cardiovasc Comput Tomogr (2008) 2, 351-359DSCT (128 x 2) vs 320 MDCT
- In presence of high HR the DSCT maintains its temporal resolution due to rotation time and table travel speed
- 320-MDCT needs multi-segment reconstruction from 2-3 heart beats to increase temporal resolution and obtain adequate image qualityRadiation Dose
- 64 MDCT with retrospective gating (8-18 mSv)
- 64 MDCT with prospective gating (1-5 mSv)
- 320 MDCT (<5 mSv)
- DSCT with FLASH (128 detectors x 2) (<1-3 mSv)Radiation Dose
- 64 MDCT with retrospective gating
- 64 MDCT with prospective gating
- 320 MDCT
- DSCT with FLASH (128 detectors x 2)320 MDCT (Acquilion One)
- 320 x 0.5 mm
- .35 sec gantry rotation time
- Longitudinal coverage of 160 mm per rotation
- Temporal resolution of 175 ms64 MDCT: challenges
-Temporal resolution
- Spatial resolution
- Scan times
- Radiation dose"Cardiac coverage MDCT with a 256- or 320-detectors provides advantages over 64-slice MDCT in terms of important image quality, reductions in radiation and contrast dose and imaging in the setting of arrhythmia or irregular heart rates."
Recent Developments in Wide-Detector Cardiac Computed Tomography
Choi SI et al
Int J Cardiovasc Imaging (2009) 25:23-29Volume CT Scanners (256/320 MDCT): Potential Issues in Cardiac CT
- Issues with data distortion in cases of arrhthymias or ectopic beats
- Increased x-ray scatter can result in increased image noise and streaking artifactsDirection in CT Technology
- Increased detector width (scan heart in one rotation)
- Increase spiral pitch (usually .2 and can go to 3.4). With a 38.4 mm detector coverage and 0.28 second gantry rotation time, a table feed of 430 mm/sec is obtained so a heart can be scanned in under .3 sec)Can We Improve Temporal Resolution?
- Faster gantry rotation (under .2 sec)
- Multiple x-rays tubes (with tube rotation speed constant)
- Multisegment reconstruction plans (limited at high or irregular heart ratesCan spatial resolution be increased w/o dose issues?
- New detector materials for scanners
- Improved detector electronics
- Post processing of data improvements ( Iterative reconstruction algorithms instead of standard filtered back projection of CT data)"To double the resolution without affecting image noise. Eg, to achieve 0.25 isotrophic resolution instead of 0.5 mm, the dose needs to be increased by a factor of 2 to the 4th (16 fold increase)."
Cardiac CT: How much can temporal resolution,spatial resolution, and volume coverage be improved?
Flohr TG, Raupach R, Bruder H
J Cardiovas Comput Tomogr (2009) 3; 143-152What is the consequence of limited resolution?
- "calcium blooming" artifact is due to insufficient spatial resolution (and at high HR to limited temporal resolution)
- Limited ability to reliably characterize plaque composition (lipid rich and fibrous plaques)- "In this article we review the current status and discuss potential further improvements and limitations of system parameters relevant for cardiac CT, in particular spatial resolution, temporal resolution and volume coverage."
Cardiac CT: How much can temporal resolution,spatial resolution, and volume coverage be improved?
Flohr TG, Raupach R, Bruder H
J Cardiovas Comput Tomogr (2009) 3; 143-152 "Acceptable image quality was achieved in 100% (30/30) of cases for the ascending aorta, 97% (29/30) of cases for the aortic valve, and 98% (442/452) of coronary artery segments."
Survey of Aorta and Coronary Arteries With Prospective ECG-Triggered 100-kV 64-MDCT Angiography
Fujioka C et al.
AJR 2009; 193:227-233" For patients with a heart rate less than 75 beats/min, prospective ECG-triggered axial CT angiography at a tube voltage of 100 kV has the potential to provide clinically relevant information about the aorta and coronary arteries with low radiation dose."
Survey of Aorta and Coronary Arteries With Prospective ECG-Triggered 100-kV 64-MDCT Angiography
Fujioka C et al.
AJR 2009; 193:227-233- "The use of lower tube voltage leads to significant reduction in radiation exposure in noninvasive coronary CT angiography. Image quality in nonobese patients is not negatively influenced."
Image Quality in a Low Radiation Exposure Protocol for Retrospectively ECG-Gated Coronary CT Angiography
Pflederer T et al.
AJR 2009; 192:1045-1050 - Cardiac: Coronary Angiography: What are the critical factors?
- Temporal resolution is 8 milliseconds
- Spatial resolution is 0.2 mm
- Radiation dose is 2 to 6 mSv