Christoph R. Becker, MD

    Increasing efforts to screen and diagnose coronary artery disease have used imaging modalities such as catheter angiography, ultrasound, and MRI. Electron-beam CT was, for a long time, the only CT system able to image the coronary arteries without motion artifacts. But multislice CT has advanced rapidly over the last decade,  and state-of-the-art 64-slice and dual-source CT now offer high-quality imaging of the coronary arteries, myocardium, and valves, providing morphological and even functional information. 

    Coronary calcium is a surrogate marker for coronary atherosclerosis, and its levels have been measured by EBCT for more than a decade. Prospective cohort studies are currently under way to measure the value of coronary calcium evaluation against conventional risk factors when estimating the risk of future cardiovascular events. Initial results published from the South Bay Heart Watch study (2000 subjects) show that coronary calcium is of minor predictive value in patients with diabetes and that differences exist in terms of prevalence and progression of coronary calcium in different ethnic groups. 

 The Heinz-Nixdorf RECALL study (4200 subjects) provides unbiased information on the extent of coronary calcium in the general German population. 

    The authors of the Prospective Army Coronary Calcium study (2000 40 to 50-year-old subjects) found the CT-based assessment of coronary calcium to be superior to the conventional Framingham risk score when determining the likelihood of future cardiac events. Similar predictive value has been found for individuals with coronary calcium and a positive family history of coronary heart disease. But at a cost of $37,633 per quality-adjusted life year saved, screening for coronary artery disease under these circumstances does not seem to be cost-effective.

    The Multi Ethnic Study of Atherosclerosis (6800 subjects) has reported that all MSCT systems are at least as reliable as EBCT for performing and reproducing coronary calcium measurements.  

  Further studies are needed to determine whether MSCT coronary calcium screening is a more cost-effective option. 

    Cardiac CT angiography is now sufficiently robust to be used routinely for a number of clinical applications. More than 16 published studies have compared 64-slice CT with coronary angiography for the detection of coronary artery stenoses. These papers, which together draw on data from 1400 patients, conclude that on average 95% of all coronary segments are fully accessible and can be compared to cardiac catheter findings. Sensitivity, specificity, and positive and negative predictive values have been reported as 85%, 96%, 85%, and 96%, respectively. Because of the high negative predictive value, most investigators have looked specifically into patient cohorts with a low to intermediate likelihood (prevalence 22%) of coronary artery disease. 

    The detection of coronary artery stenoses on CT may still be hindered by collateral flow, retrograde filling, plaque formation with positive vessel remodeling, and extensive calcifications. Grading the degree of stenosis remains a challenge as well, as a result of CT’s limited spatialresolution. 

    The noninvasive nature of cardiac CT means that it is not competing directly with cardiac catheterization. It should be viewed instead as a triaging tool to determine whether patients are treated conservatively or referred for invasive therapy. This approach may put CTA in direct competition with the nuclear stress or ECG treadmill test. A head-to-head comparison between stress ECG and cardiac CT showed CT to have a significantly higher sensitivity (91% versus 73%) and specificity (83% versus 31%). CT was unable to assess 8% of patients, while stress ECG failed to evaluate 19% of study subjects. >

    The reliability and efficiency of cardiac CT depend greatly on the pretest probability of patients for coronary artery disease. Assuming the costs of cardiac catheterization, CT, ultrasound, and stress ECG to be approximately $930, $259, $192, and $44, respectively, CT is the most cost-efficient modality up to a pretest likelihood of 50%. 

    The clinical implication is that patients with nonanginal chest pain and women with atypical angina may benefit from cardiac CT as a rapid test  for excluding coronary artery disease. Cardiac CT may also serve as an alternative to immediate cardiac catheterization in younger male patients with atypical chest pain and in younger women, even those with typical angina. 

    Cardiac CTA may also offer a practical option for triaging patients with acute chest pain. This is evidenced in a study of 200 patients reported earlier this year. 

 The study subjects, all of whom presented with acute chest pain, were randomly assigned to either the stan dard of care with a nuclear stress test or an alternative pathway that included cardiac CT triaging prior to further workup. Patients’ workup was faster (3.4 hours versus 15 hours) and cheaper ($1586 versus $1872) in the cardiac CT arm.  

    Only two patients from the CT group returned after a certain period with recurrent chest pain, compared with seven patients in the standard care arm. The combination of a rapid morphological test and an on-demand functional test would appear to be the ideal way of reaching a valid diagnosis in this cohort. 

    Data suggest that CTA may additionally be a valid diagnostic approach in patients with coronary artery stents (Figure 1).  

  Cardiac CT won’t reveal any information about myocardial perfusion in patients with myocardial ischemia, however. The technique is consequently of limited value when coronary symptoms are present. Small stents are still difficult to assess, and in-stent stenosis cannot be ruled out. 

    The introduction of 64-slice CT has improved the reliability of coronary artery bypass grafts. The accuracy of arterial and venous grafts is in the range of 98%. Distal runoff or nongrafted coronary artery segments are commonly difficult to assess, however, because the original vessels in patients with bypass grafts are so often severely calcified. 

    Patients requiring further surgery after a bypass procedure will benefit from the ability of cardiac CT to visualize grafts concisely, in particular grafts that run behind the sternum. 

  This gives cardiac CT a clear advantage over conventional radiography and cardiac catheterization in this patient group (Figure 2). 

  Cardiac CT also appears to be a preferable screening tool for patients undergoing cardiac surgery for reasons other than coronary artery disease. 

    Cardiac CT is frequently requested for patients with atrial fibrillation who are scheduled for catheter ablation. The visualization of left atrium anatomy on CT helps to determine any accessory or anomalous courses of the pulmonary veins (Figure 3). 

  CT data from the heart can be input into commercially available software to plan and guide the procedure. 

 It is also important to rule out coronary artery disease in this particular cohort of patients because anti-arrhythmic medical therapy may provoke arrhythmia if it is present. 

    It may be desirable to achieve high, homogeneous enhancement in the coronary arteries, aorta, and pulmonary arteries in a single examination for patients with ambiguous symptoms in the chest. This means maintaining the contrast bolus for the entire scan and during the passage of the bolus from the pulmonary arteries to the coronary arteries (Figure 4). 

 A protocol of this type would provide comprehensive information on possible differential diagnoses, such as aortic dissection, pulmonary embolism, degenerative spine disease, esophagitis, and tumor manifestation. Patients would, however, be exposed to a significant amount of radiation. 

    CT is superior to MR imaging for displaying coronary artery morphology, whereas MRI is preferable to CT when  information about myocardial function is needed. A combination of both modalities is sometimes required to gain the most accurate diagnosis. It is thus hard to believe that CT will ever serve as a one-stop shop for any cardiac disease.  Cardiac CT is more likely to fit into the cardiology environment as a cost-effective method of making a quick and efficient decision on the most appropriate therapy in patients with low to moderate risk of coronary artery disease. 

    1. Greenland P, LaBree L, Azen SP, et al. Coronary artery calcium score combined with Framingham score for risk prediction in asymptomatic individuals. JAMA 2004;291(2):210-215. 

    2. Schmermund A, Mohlenkamp S, Berenbein S, et al. Population-based assessment of subclinical coronary atherosclerosis using electron-beam computed tomography. Atherosclerosis 2006; 185(1):177-182. 

    3. Taylor AJ, Bindeman J, Feuerstein I, et al. Coronary calcium independently predicts incident premature coronary heart disease over measured cardiovascular risk factors: mean three-year outcomes in the Prospective Army Coronary Calcium (PACC) project. J Am Coll Cardiol 2005;46(5):807-814. 

    4. Detrano RC, Anderson M, Nelson J, et al. Coronary calcium measurements: effect of CT scanner type and calcium measure on rescan reproducibility-MESA study. Radiology 2005; 236(2):477-484. 

    5. Leschka S, Alkadhi H, Plass A, et al. Accuracy of MSCT coronary angiography with 64-slice technology: first experience. Europ Heart J 2005;15(6):1203-1210. 

    6. Raff GL, Gallagher MJ, O’Neill WW, Goldstein JA. Diagnostic accuracy of noninvasive coronary angiography using 64-slice spiral computed tomography. J Am Coll Cardiol 2005;46(3):552-557. 

    7. Mollet NR, Cademartiri F, van Mieghem CA, et al. High-resolution spiral computed tomography coronary angiography in patients referred for diagnostic conventional coronary angiography. Circulation 2005;112(15):2318-2323. 

    8. Leber AW, Becker A, Knez A, et al. Accuracy of 64-slice computed tomography to classify and quantify plaque volumes in the  proximal coronary system: a comparative study using intravascular ultrasound. J Am Coll Cardiol 2006;47(3):672-677. 

    9. Dewey M, Dubel HP, Schink T, et al. Head-to-head comparison of multislice computed tomography and exercise electrocardiography for diagnosis of coronary artery disease. Europ Heart J 2006; epub 31 July (doi:10.1093/eurheartj/ehl148). 

    10. Dewey M, Hamm B. Cost effectiveness of coronary angiography and calcium scoring using CT and stress MRI for diagnosis of coronary artery disease. Europ Radiol 2007;17(5):1301-1309. 

    11. Gibbons R, Chatterjee K, Daley J, et al. ACC/AHA/ACP-ASIM guidelines for the management of patients with chronic stable angina: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Patients With Chronic Stable Angina). J Am Coll Cardiol 1999;33(7):2092-2197. 

    12. Goldstein JA, Gallagher MJ, O’Neill WW, et al. A randomized controlled trial of multi-slice coronary computed tomography for evaluation of acute chest pain. J Am Coll Cardiol 2007;49(8):    863-871. 

    13. Oncel D, Oncel G, Karaca M. Coronary stent patency and in-stent restenosis: determination with 64-section multidetector CT coronary angiography-initial experience. Radiology 2007; 242(2):    403-409. 

    14. Malagutti P, Nieman K, Meijboom WB, et al. Use of 64-slice CT in symptomatic patients after coronary bypass surgery: evaluation of grafts and coronary arteries. Europ Heart J 2006; epub 17 July (doi:10.1093/eurheartj/ehl155). 

    15. Aviram G, Sharony R, Kramer A, et al. Modification of surgical planning based on cardiac multidetector computed tomography in reoperative heart surgery. Ann Thorac Surg 2005;79(2):589-595. 

    16. Gasparovic H, Rybicki FJ, Millstine J, et al. Three dimensional computed tomographic imaging in planning the surgical approach for redo cardiac surgery after coronary revascularization. Europ J Cardiothorac Surg 2005;28(2):244-249. 

    17. Russo V, Gostoli V, Lovato L, et al. Clinical value of multidetector CT coronary angiography as a pre-operative screening test before noncoronary cardiac surgery. Heart 2006; epub Dec (doi:    10.1136/hrt.2006.105026). 

    18. Jongbloed MR, Dirksen MS, Bax JJ, et al. Atrial fibrillation: multi-detector row CT of pulmonary vein anatomy prior to radiofrequency catheter ablation-initial experience. Radiology 2005;234(3):702-709. 

    19. Centonze M, Del Greco M, Nollo G, et al. The role of multidetector CT in the evaluation of the left atrium and pulmonary veins anatomy before and after radio-frequency catheter ablation for atrial fibrillation. Preliminary results and work in progress. Technical note. Radiol Med (Torino) 2005;110(1-2):52-60. 

    20. Johnson TR, Nikolaou K, Wintersperger BJ, et al. ECG-gated 64-MDCT angiography in the differential diagnosis of acute chest pain. AJR 2007;188(1):76-82. 

Articles

Dual-source or 64-slice CT examination proves quick, noninvasive, and effective in triaging patients with low to moderate risk of heart disease

Cardiac CT exhibits clinical, cost benefits despite radiation risk

Increasing efforts to screen and diagnose coronary artery disease have used imaging modalities such as catheter angiography, ultrasound, and MRI. Electron-beam CT was, for a long time, the only CT system able to image the coronary arteries without motion artifacts. But multislice CT has advanced rapidly over the last decade, and state-of-the-art 64-slice and dual-source CT now offer high-quality imaging of the coronary arteries, myocardium, and valves, providing morphological and even functional information.

Coronary calcium is a surrogate marker for coronary atherosclerosis, and its levels have been measured by EBCT for more than a decade. A number of prospective cohort studies are currently under way to measure the value of coronary calcium evaluation against conventional risk factors when estimating the risk of future cardiovascular events. Initial results published from the South Bay Heart Watch study (2000 subjects) show that coronary calcium is of minor predictive value in patients with diabetes and that differences exist in terms of prevalence and progression of coronary calcium in different ethnic groups.1 The Heinz-Nixdorf RECALL study (4200 subjects) provides unbiased information on the extent of coronary calcium in the general German population.2

The authors of the Prospective Army Coronary Calcium study (2000 40 to 50-year-old subjects) found the CT-based assessment of coronary calcium to be superior to the conventional Framingham risk score when determining the likelihood of future cardiac events. Similar predictive value has been found for individuals with coronary calcium and a positive family history of coronary heart disease. But at a cost of $37,633 per quality-adjusted life year saved, screening for coronary artery disease under these circumstances does not seem to be cost-effective.3

The Multi Ethnic Study of Atherosclerosis (6800 subjects) has reported that all MSCT systems are at least as reliable as EBCT for performing and reproducing coronary calcium measurements.4 Further studies are needed to determine whether MSCT coronary calcium screening is a more cost-effective option.

Cardiac CT angiography is now sufficiently robust to be used routinely for a number of clinical applications. More than 16 published studies have compared 64-slice CT with coronary angiography for the detection of coronary artery stenoses. These papers, which together draw on data from 1400 patients, conclude that on average 95% of all coronary segments are fully accessible and can be compared to cardiac catheter findings. Sensitivity, specificity, and positive and negative predictive values have been reported as 85%, 96%, 85%, and 96%, respectively. Because of the high negative predictive value, most investigators have looked specifically into patient cohorts with a low to intermediate likelihood (prevalence 22%) of coronary artery disease.5-8

The detection of coronary artery stenoses on CT may still be hindered by collateral flow, retrograde filling, plaque formation with positive vessel remodeling, and extensive calcifications. Grading the degree of stenosis remains a challenge as well, as a result of CT's limited spatial resolution.

The noninvasive nature of cardiac CT means that it is not competing directly with cardiac catheterization. It should be viewed instead as a triaging tool to determine whether patients are treated conservatively or referred for invasive therapy. This approach may put CTA in direct competition with the nuclear stress or ECG treadmill test. A head-to-head comparison between stress ECG and cardiac CT showed CT to have a significantly higher sensitivity (91% versus 73%) and specificity (83% versus 31%). CT was unable to assess 8% of patients, while stress ECG failed to evaluate 19% of study subjects.9

The reliability and efficiency of cardiac CT depend greatly on the pretest probability of patients for coronary artery disease. Assuming the costs of cardiac catheterization, CT, ultrasound, and stress ECG to be approximately Euro 630, Euro 175, Euro 130, and Euro 30, respectively, CT is the most cost-efficient modality up to a pretest likelihood of 50%.10

The clinical implication is that patients with nonanginal chest pain and women with atypical angina may benefit from cardiac CT as a rapid test for excluding coronary artery disease. Cardiac CT may also serve as an alternative to immediate cardiac catheterization in younger male patients with atypical chest pains and in younger females, even those with typical angina.11

Cardiac CTA may also offer a practical option for triaging patients with acute chest pain. This is evidenced in a study of 200 patients reported earlier this year.12 Study subjects, all of whom presented with acute chest pain, were randomly assigned to either the standard of care with a nuclear stress test or an alternative pathway that included cardiac CT triaging prior to further workup. Patients' workup was faster (3.4 hours versus 15 hours) and cheaper ($1586 versus $1872) in the cardiac CT arm.

Only two patients from the CT group returned after a certain period with recurrent chest pain, compared with seven patients in the standard care arm. The combination of a rapid morphological test and an on-demand functional test would appear to be the ideal way of reaching a valid diagnosis in this cohort.

Data suggest that CTA may additionally be a valid diagnostic approach in patients with coronary artery stents (Figure 1).13 Cardiac CT won't reveal any information about myocardial perfusion in patients with myocardial ischemia, however. The technique is consequently of limited value when coronary symptoms are present. Small stents are still difficult to assess, and in-stent stenosis cannot be ruled out.

The introduction of 64-slice CT has improved the reliability of coronary artery bypass grafts. The accuracy of arterial and venous grafts is in the range of 98%. Distal runoff or nongrafted coronary artery segments are commonly difficult to assess, however, because the original vessels in patients with bypass grafts are so often severely calcified.14

Patients requiring further surgery after a bypass procedure will benefit from the ability of cardiac CT to visualize grafts concisely, in particular grafts that run behind the sternum.15 This gives cardiac CT a clear advantage over conventional radiography and cardiac catheterization in this patient group (Figure 2).16 Cardiac CT also appears to be a preferable screening tool for patients undergoing cardiac surgery for reasons other than coronary artery disease.17

Cardiac CT is frequently requested for patients with atrial fibrillation who are scheduled for catheter ablation. The visualization of left atrium anatomy on CT helps to determine any accessory or anomalous courses of the pulmonary veins (Figure 3).18 CT data from the heart can be input into commercially available software to plan and guide the procedure.19 It is also important to rule out coronary artery disease in this particular cohort of patients because anti-arrhythmic medical therapy may provoke arrhythmia if it is present.

It may be desirable to achieve high, homogeneous enhancement in the coronary arteries, aorta, and pulmonary arteries in a single examination for patients with ambiguous symptoms in the chest. This means maintaining the contrast bolus for the entire scan and during the passage of the bolus from the pulmonary arteries to the coronary arteries (Figure 4).20 A protocol of this type would provide comprehensive information on possible differential diagnoses, such as aortic dissection, pulmonary embolism, degenerative spine disease, esophagitis, and tumor manifestation. Patients would, however, be exposed to a significant amount of radiation.

CT is superior to MR imaging for displaying coronary artery morphology, whereas MRI is preferable to CT when seeking information about myocardial function. A combination of both modalities is sometimes required to gain the most accurate diagnosis. It is thus hard to believe that CT will ever serve as a one-stop shop for any cardiac disease. Cardiac CT is more likely to fit into the cardiology environment as a cost-effective method of deciding quickly and efficiently on the most appropriate therapy in patients with low to moderate risk of coronary artery disease.

Greenland P, LaBree L, Azen SP, et al. Coronary artery calcium score combined with Framingham score for risk prediction in asymptomatic individuals. JAMA 2004;291(2):210-215.

Schmermund A, Mohlenkamp S, Berenbein S, et al. Population-based assessment of subclinical coronary atherosclerosis using electron-beam computed tomography. Atherosclerosis 2006; 185(1):177-182.

Taylor AJ, Bindeman J, Feuerstein I, et al. Coronary calcium independently predicts incident premature coronary heart disease over measured cardiovascular risk factors: mean three-year outcomes in the Prospective Army Coronary Calcium (PACC) project. J Am Coll Cardiol 2005;46(5):807-814.

Detrano RC, Anderson M, Nelson J, et al. Coronary calcium measurements: effect of CT scanner type and calcium measure on rescan reproducibility-MESA study. Radiology 2005; 236(2):477-484.

Leschka S, Alkadhi H, Plass A, et al. Accuracy of MSCT coronary angiography with 64-slice technology: first experience. Europ Heart J 2005;15(6):1203-1210.

Raff GL, Gallagher MJ, O'Neill WW, Goldstein JA. Diagnostic accuracy of noninvasive coronary angiography using 64-slice spiral computed tomography. J Am Coll Cardiol 2005;46(3):552-557.

Mollet NR, Cademartiri F, van Mieghem CA, et al. High-resolution spiral computed tomography coronary angiography in patients referred for diagnostic conventional coronary angiography. Circulation 2005;112(15):2318-2323.

Leber AW, Becker A, Knez A, et al. Accuracy of 64-slice computed tomography to classify and quantify plaque volumes in the proximal coronary system: a comparative study using intravascular ultrasound. J Am Coll Cardiol 2006;47(3):672-677.

Dewey M, Dubel HP, Schink T, et al. Head-to-head comparison of multislice computed tomography and exercise electrocardiography for diagnosis of coronary artery disease. Europ Heart J 2006; epub 31 July (doi:10.1093/eurheartj/ehl148).

Dewey M, Hamm B. Cost effectiveness of coronary angiography and calcium scoring using CT and stress MRI for diagnosis of coronary artery disease. Europ Radiol 2007;17(5):1301-1309.

Gibbons R, Chatterjee K, Daley J, et al. ACC/AHA/ACP-ASIM guidelines for the management of patients with chronic stable angina: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Patients With Chronic Stable Angina). J Am Coll Cardiol 1999;33(7):2092-2197.

Goldstein JA, Gallagher MJ, O'Neill WW, et al. A randomized controlled trial of multi-slice coronary computed tomography for evaluation of acute chest pain. J Am Coll Cardiol 2007;49(8):863-871.

Oncel D, Oncel G, Karaca M. Coronary stent patency and in-stent restenosis: determination with 64-section multidetector CT coronary angiography-initial experience. Radiology 2007; 242(2):403-409.

Malagutti P, Nieman K, Meijboom WB, et al. Use of 64-slice CT in symptomatic patients after coronary bypass surgery: evaluation of grafts and coronary arteries. Europ Heart J 2006; epub 17 July (doi:10.1093/eurheartj/ehl155).

Aviram G, Sharony R, Kramer A, et al. Modification of surgical planning based on cardiac multidetector computed tomography in reoperative heart surgery. Ann Thorac Surg 2005;79(2):589-595.

Gasparovic H, Rybicki FJ, Millstine J, et al. Three dimensional computed tomographic imaging in planning the surgical approach for redo cardiac surgery after coronary revascularization. Europ J Cardiothorac Surg 2005;28(2):244-249.

Russo V, Gostoli V, Lovato L, et al. Clinical value of multidetector CT coronary angiography as a pre-operative screening test before noncoronary cardiac surgery. Heart 2006; epub Dec (doi:10.1136/hrt.2006.105026).

Jongbloed MR, Dirksen MS, Bax JJ, et al. Atrial fibrillation: multi-detector row CT of pulmonary vein anatomy prior to radiofrequency catheter ablation-initial experience. Radiology 2005;234(3):702-709.

Centonze M, Del Greco M, Nollo G, et al. The role of multidetector CT in the evaluation of the left atrium and pulmonary veins anatomy before and after radio-frequency catheter ablation for atrial fibrillation. Preliminary results and work in progress. Technical note. Radiol Med (Torino) 2005;110(1-2):52-60.

Johnson TR, Nikolaou K, Wintersperger BJ, et al. ECG-gated 64-MDCT angiography in the differential diagnosis of acute chest pain. AJR 2007;188(1):76-82.

DR. BECKER is chief of body CT and PET/CT at the Grosshadern Clinic, Munich University Hospital, in Germany.

Cardiac CT exhibits both clinical and cost benefits

Dual-source CT represents a significant advance for coronary CT angiography. In our preliminary experience, it has made CTA more robust and provided reliable assessment of vessel wall irregularities and stenoses without motion artifacts. Radiation exposure can be reduced significantly compared with conventional CTA.

DSCT was primarily developed to increase temporal resolution, which is a crucial factor in cardiac imaging. As the coronary arteries move rapidly during most parts of the cardiac cycle, the benchmark for imaging is the ability to freeze these arteries during the small time window of slow motion. In low heart rates, this has been possible with gantry rotation times of 0.3 to 0.5 seconds, which define the temporal resolution of the system. In higher heart rates, however, the diastolic window of time for slow coronary motion, about 150 to 200 msec,

 diminishes. The diagnostic evaluation of stenoses or vessel wall irregularities becomes unreliable or even impossible due to the increased blurring of the coronary arteries.

CT system components are exposed to high g-forces, and it has been a major technical challenge to construct a gantry that can mechanically withstand them. To date, no manufacturer has been able to decrease the rotation time beyond 0.33 seconds in commercially available systems. Improving temporal resolution required a new approach: DSCT.

In recent years, developments in tube technology with externally cooled anodes

 have made the combination of two x-ray sources and two detectors in one gantry feasible. This concept is realized in the Siemens DSCT scanner,

 making it possible to acquire projection data for one image in a quarter rotation of the gantry. This doubles the temporal resolution at a given gantry rotation speed. As a result, a temporal resolution of 83 msec can be achieved at a gantry rotation time of 0.33 seconds.

We are now applying the theoretical advantages of the DSCT system in a clinical setting. Generally, the higher temporal resolution makes cardiac imaging more robust and improves image quality, especially in patients with irregular heartbeats or high heart rates. It is not necessary to lower the heart rate to below 60 beats per minute with beta blockers as we have done in the past. Instead, we now apply nitroglycerine spray, which has been shown to significantly dilate the coronary arteries.

 The reflex tachycardia resulting from vasodilatation is considered a drawback of this approach to coronary CTA, but the increased heart-rate insensitivity of DSCT outweighs this disadvantage, by offering a larger vessel diameter for assessing wall irregularities.

Regarding arrhythmia, in the past it was possible to eliminate ectopic beats by editing the ECG trace. Now the high image quality that can be achieved in the short systolic window of the cardiac cycle makes it possible to obtain diagnostic images even in patients with atrial fibrillation.

 we were able to acquire diagnostic images in all 24 patients with heart rates between 44 and 92 bpm. Since then, we have successfully imaged various patients at heart rates over 100 bpm (Figure 1). Our study shows that a reliably high diagnostic image quality can be obtained at 70% of the cardiac cycle in heart rates of up to 70 bpm, while in higher heart rates the best image quality is frequently found in systole (i.e., at 30% to 40% of the cardiac cycle).

We have been able to decrease radiation exposure by reducing the pulsing window for ECG-triggered tube current modulation,

 applying the full current only for a duration of about 10% of the cardiac cycle in diastole. In higher heart rates, we set the pulsing window to 30% to 80% of the cardiac cycle, which makes both systolic and diastolic reconstruction possible. Still, using a heart rate-dependent pitch adaptation, the radiation exposure is significantly reduced as compared with conventional CTA, as we have been able to verify in our own dose measurements.

The increased image quality and stable continuity of the depicted vessels over the slabs in the z-axis also improve the performance of postprocessing software. In most data sets, it is now possible to segment the whole coronary artery tree with a single click into the aortic root. The arteries can be evaluated at a glance, and curved multiplanar reconstructions help evaluate vessel wall changes. Quantification of stenoses appears more reliable and correlates better with quantitative analysis of invasive biplanar coronary angiography. Preliminary results from our prospective study demonstrate more reliable results from software-assisted quantification compared with "eyeballing."

Static morphological depiction of the coronary arteries is not all that is improved with DSCT. The high temporal resolution makes it possible to visualize the vessel lumen during most of the cardiac cycle. This can be of diagnostic value in intramural segments, or myocardial bridging, of the coronary arteries, which can represent a cause of exercise angina that is frequently missed in conventional coronary angiography. The dynamic visualization of the lumen in this segment can help to assess the severity of compression during systole.

This dynamic information provides a new aspect to functional imaging with coronary CTA. In addition, wall motion is depicted without distortion as a concentric contraction in short-axis slices, which should make the detection of wall motion abnormalities more reliable. With 83 msec temporal resolution, it should also be possible to match the smallest ventricle volume in an end-systolic image exactly, offering a reliable quantification of ejection fraction. Limited temporal resolution and an underestimation of ejection fraction have been drawbacks of functional evaluation in CT, but this important information is now easily assessable and can be quantified routinely from CTA data sets.

DSCT also yields another rather unexpected advantage: very good depiction of the heart valves (Figure 2). Depending on the contrast injection regimen, typically only the blood around the mitral and aortic valve is sufficiently opacified. As a result, the individual leaflets of the valve and their motion during the cardiac cycle can be observed, making it possible to exclude valve stenoses or high-grade insufficiency. In an orthogonal reconstruction (Figure 2B), the exact opening area can be quantified as well, if the pulsing interval is adapted to depict the phase of the largest opening at about 10% with full tube current.

Another advantage of the new system is a protocol specifically designed for chest pain assessment. With this protocol, one tube and detector acquire a normal spiral scan of the chest. The second tube is switched on at the level of the carina to provide the high temporal resolution necessary for coronary imaging. Thus radiation exposure is limited to a minimum, and the whole vasculature of the chest can evaluated for the cause of the chest pain. With a suitable contrast injection regimen,

 pulmonary arteries, coronary arteries, and the aorta can be evaluated for pulmonary embolism, coronary artery stenoses, or aortic dissection, with full diagnostic angiographic image quality in a single breath-hold scan at a radiation dose significantly below 10 mSv.

In our experience, DSCT has made coronary CTA more robust and eliminates the need for beta blockers. Reliable assessment of vessel wall irregularities and stenoses is improved by the absence of motion artifacts and facilitates postprocessing. With optimized ECG-triggered tube current modulation, radiation exposure can be reduced greatly compared with conventional CT. The added dynamic information, including wall motion, ventricular function, and valve function, increases the diagnostic value of cardiac CT beyond coronary angiography.

DRS. JOHNSON and NIKOLAOU are radiologists in the department of clinical radiology at Munich University. DR. BECKER is an associate professor of radiology and section chief of computed tomography at Grosshadern Hospital at the University of Munich.

 Wang Y, Vidan E, Bergman GW. Cardiac motion of coronary arteries: variability in the rest period and implications for coronary MR angiography. Radiology 1999;213:751-758.


 Wintersperger BJ, Nikolaou K, Ziegler Fv, et al. Image quality, motion artifacts, and reconstruction timing of 64-slice coronary computed tomography angiography with 0.33-second rotation speed. Invest Radiol 2006;41:in press.


 Schardt P, Deuringer J, Freudenberger J, et al. New x-ray tube performance in computed tomography by introducing the rotating envelope tube technology. Med Phys 2004;31:2699-2706.


 Flohr TG, McCollough CH, Bruder H, et al. First performance evaluation of a dual-source CT (DSCT) system. Eur Radiol 2006;16:256-268.


 Dewey M, Hoffmann H, Hamm B. Multislice CT coronary angiography: effect of sublingual nitroglycerine on the diameter of coronary arteries. Rofo 2006;178:600-604.


 Johnson TR, Nikolaou K, Wintersperger BJ, et al. Dual-source CT cardiac imaging: initial experience. Eur Radiol 2006;16:1409-1415.


 Jakobs TF, Becker CR, Ohnesorge B, et al. Multislice helical CT of the heart with retrospective ECG gating: reduction of radiation exposure by ECG-controlled tube current modulation. Eur Radiol 2002;12:1081-1086.


 Johnson TRC, Nikolaou K, Wintersperger BJ, et al. Optimization of contrast material administration for electrocardiogram-gated computed tomographic angiography of the chest. JCAT 2006;30:in press.


Johnson TRC, Nikolaou K, Wintersperger BJ, et al. ECG-gated 64-slice CT angiography for the differential diagnosis of acute chest pain. AJR 2007:in press.

Dual-source CT advances coronary angiography

New approach increases temporal resolution, improving cardiac image quality while adding dynamic functional information 

DSCT was primarily developed to increase temporal resolution, which is a crucial factor in cardiac imaging. As the coronary arteries move rapidly during most parts of the cardiac cycle, the benchmark for imaging is the ability to freeze these arteries during the small time window of slow motion. In low heart rates, this has been possible with gantry rotation times of 0.3 to 0.5 seconds, which define the temporal resolution of the system. In higher heart rates, however, the diastolic window of time for slow coronary motion, about 150 to 200 msec,1 diminishes. The diagnostic evaluation of stenoses or vessel wall irregularities becomes unreliable or even impossible due to the increased blurring of the coronary arteries.2

In recent years, developments in tube technology with externally cooled anodes3 have made the combination of two x-ray sources and two detectors in one gantry feasible. This concept is realized in the Siemens DSCT scanner,4 making it possible to acquire projection data for one image in a quarter rotation of the gantry. This doubles the temporal resolution at a given gantry rotation speed. As a result, a temporal resolution of 83 msec can be achieved at a gantry rotation time of 0.33 seconds.

We are now applying the theoretical advantages of the DSCT system in a clinical setting. Generally, the higher temporal resolution makes cardiac imaging more robust and improves image quality, especially in patients with irregular heartbeats or high heart rates. It is not necessary to lower the heart rate to below 60 beats per minute with beta blockers as we have done in the past. Instead, we now apply nitroglycerine spray, which has been shown to significantly dilate the coronary arteries.5 The reflex tachycardia resulting from vasodilatation is considered a drawback of this approach to coronary CTA, but the increased heart-rate insensitivity of DSCT outweighs this disadvantage, by offering a larger vessel diameter for assessing wall irregularities.

In our first clinical study,6 we were able to acquire diagnostic images in all 24 patients with heart rates between 44 and 92 bpm. Since then, we have successfully imaged various patients at heart rates over 100 bpm (Figure 1). Our study shows that a reliably high diagnostic image quality can be obtained at 70% of the cardiac cycle in heart rates of up to 70 bpm, while in higher heart rates the best image quality is frequently found in systole (i.e., at 30% to 40% of the cardiac cycle).

We have been able to decrease radiation exposure by reducing the pulsing window for ECG-triggered tube current modulation,7 applying the full current only for a duration of about 10% of the cardiac cycle in diastole. In higher heart rates, we set the pulsing window to 30% to 80% of the cardiac cycle, which makes both systolic and diastolic reconstruction possible. Still, using a heart rate-dependent pitch adaptation, the radiation exposure is significantly reduced as compared with conventional CTA, as we have been able to verify in our own dose measurements.

Another advantage of the new system is a protocol specifically designed for chest pain assessment. With this protocol, one tube and detector acquire a normal spiral scan of the chest. The second tube is switched on at the level of the carina to provide the high temporal resolution necessary for coronary imaging. Thus radiation exposure is limited to a minimum, and the whole vasculature of the chest can evaluated for the cause of the chest pain. With a suitable contrast injection regimen,8 pulmonary arteries, coronary arteries, and the aorta can be evaluated for pulmonary embolism, coronary artery stenoses, or aortic dissection, with full diagnostic angiographic image quality in a single breath-hold scan at a radiation dose significantly below 10 mSv.9

Drs. Johnson and Nikolaou are radiologists in the department of clinical radiology at Munich University. Dr. Becker is an associate professor of radiology and section chief of computed tomography at Grosshadern Hospital at the University of Munich. Dr. Johnson has served as consultant for Siemens Medical Solutions.

1. Wang Y, Vidan E, Bergman GW. Cardiac motion of coronary arteries: variability in the rest period and implications for coronary MR angiography. Radiology 1999;213:751-758.

2. Wintersperger BJ, Nikolaou K, Ziegler Fv, et al. Image quality, motion artifacts, and reconstruction timing of 64-slice coronary computed tomography angiography with 0.33-second rotation speed. Invest Radiol 2006;41:in press.

3. Schardt P, Deuringer J, Freudenberger J, et al. New x-ray tube performance in computed tomography by introducing the rotating envelope tube technology. Med Phys 2004;31:2699-2706.

4. Flohr TG, McCollough CH, Bruder H, et al. First performance evaluation of a dual-source CT (DSCT) system. Eur Radiol 2006;16:256-268.

5. Dewey M, Hoffmann H, Hamm B. Multislice CT coronary angiography: effect of sublingual nitroglycerine on the diameter of coronary arteries. Rofo 2006;178:600-604.

6.Johnson TR, Nikolaou K, Wintersperger BJ, et al. Dual-source CT cardiac imaging: initial experience. Eur Radiol 2006;16:1409-1415.

7.Jakobs TF, Becker CR, Ohnesorge B, et al. Multislice helical CT of the heart with retrospective ECG gating: reduction of radiation exposure by ECG-controlled tube current modulation. Eur Radiol 2002;12:1081-1086.

8.Johnson TRC, Nikolaou K, Wintersperger BJ, et al. Optimization of contrast material administration for electrocardiogram-gated computed tomographic angiography of the chest. JCAT 2006;30:in press.

9.Johnson TRC, Nikolaou K, Wintersperger BJ, et al. ECG-gated 64-slice CT angiography for the differential diagnosis of acute chest pain. AJR 2007:in press.

New approach increases temporal resolution, improving cardiac image quality while adding dynamic functional information