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DOI:10.2214/AJR.05.0967
AJR 2006; 186:1676-1681
© American Roentgen Ray Society

Original Research

Diagnostic Performance of MDCT for Detecting Aortic Valve Regurgitation

Gudrun M. Feuchtner1, Wolfgang Dichtl2, Thomas Schachner3, Silvana Müller2, Ammar Mallouhi1, Guy J. Friedrich2 and Dieter zur Nedden1

1 Clinical Department of Radiology II, Innsbruck Medical University, Anichstr. 35, A-6020 Innsbruck, Austria.
2 Clinical Department of Cardiology, Innsbruck Medical University, Innsbruck, Austria.
3 Clinical Department of Cardiac Surgery, Innsbruck Medical University, Innsbruck, Austria.

Received June 7, 2005; accepted after revision September 18, 2005.

 
Address correspondence to G. M. Feuchtner (Gudrun.Feuchtner{at}uibk.ac.at).


Abstract
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 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
OBJECTIVE. This study evaluates whether ECG-gated 16-MDCT coronary angiography provides a reliable imaging technique for detecting aortic regurgitation (AR).

SUBJECTS AND METHODS. We examined 71 patients prospectively with 16-MDCT angiography using retrospective ECG gating during the mid-to-end diastolic phase. A visible central valvular leakage area was considered as a diagnostic criterion for AR. The central valvular leakage area was quantified in patients with positive transthoracic echocardiography (TTE). We compared 16-MDCT to Doppler TTE, the accepted diagnostic standard based on semiquantitative regurgitation jet analysis (grade 0-3+ for mild, moderate, and severe).

RESULTS. The overall sensitivity of 16-MDCT for the identification of patients with AR was 81%. The specificity was 91%, the negative predictive value was 70%, and the positive predictive value was 95%. Of the 71 patients, 48 had AR determined by TTE, and 16-MDCT correctly detected AR in 39 of those 48 patients. The sensitivity of 16-MDCT for the detection of patients with moderate and severe AR (grade ≥ 1.5+) was 95%, and the specificity was 96% (20 of 21 patients). The sensitivity of 16-MDCT for identification of patients with mild AR (grade ≤ 1+) was 70%, and the specificity was 92% (19 of 27 patients). Quantification of the central valvular leakage area was not possible in 50% of cases with AR by TTE because of valve calcifications.

CONCLUSION. Sixteen-MDCT coronary angiography provides an accurate, noninvasive imaging technique to detect moderate and severe aortic regurgitation (grade ≥ 1.5+). However, severe valve calcifications and mild AR limit its results.

Keywords: aortic valve disease • CT coronary angiography • CT coronary arteriography • heart • MDCT


Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
Sixteen-MDCT is a highly accurate imaging method for detecting significant coronary artery stenosis [1-4]. Also, 16-MDCT shows promising results in assessing coronary bypass graft patency [5, 6]. The comorbidity of aortic valve pathologies, such as degenerative aortic valve stenosis with concomitant aortic regurgitation (AR), is relatively high in patients with coronary artery disease. With 16-MDCT, retrospective ECG gating is used, which offers image reconstruction at any time during the cardiac cycle. The aortic valve leaflets are usually closed tightly during diastole. Accordingly, in the presence of AR, a central valvular leakage area might be detected using 16-MDCT.

This study assesses the clinical accuracy of 16-MDCT in the identification of AR in patients who undergo 16-MDCT coronary angiography, based on the visibility of a central valvular leakage area, compared with the currently accepted diagnostic standard, transthoracic echocardiography (TTE).


Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Study Population
A total of 71 patients (55 men and 16 women with a mean age of 65 years; range, 39-82 years) were examined between October 2003 and April 2005. Patient exclusion criteria were renal dysfunction and other contraindications to the iodine contrast agent (e.g., known allergy). The institutional review board approved studies on cardiac 16-MDCT in patients with degenerative aortic valve stenosis (n = 48) and in patients before or after totally endoscopic coronary bypass surgery (n = 13). The remaining patients underwent cardiac 16-MDCT for follow-up of ascending aortic aneurysm and/or evaluation of clinically suspected coronary artery disease (n =8), ascending aortic dissection with coronary ostium involvement (n = 1), or after cardiac surgery accompanied by atypical chest pain (n = 1). Written informed consent was obtained from all patients.

MDCT Examination Technique
All examinations were performed using a 16-MDCT scanner (Sensation 16, Siemens Medical Solutions) [7]. Collimation was 12 x 0.75 mm, table translation speed was 6.7 mm/sec, gantry rotation time was 0.42 sec, tube current was 400-500 mAs, tube voltage was 120 kV, and the effective radiation dose ranged between 6.7 and 13 mSv [8]. A bolus of 100-mL iodine contrast agent (iodixanol, Visipaque 320, Amersham Health) was injected IV into an antecubital vein at a flow rate of 3 to 4 mL/sec using a power injector (Ulrich Medizintechnik). Scan delay was calculated by measuring CT attenuation values at the ascending aorta using dedicated software (DynEva, Siemens Medical Solutions), after injecting a 20-mL test bolus of contrast agent. The time point of the highest CT attenuation was taken as the scan delay. Scanning was performed during a single inspiratory breath-hold of 20 to 28 sec. A ß-blocker was injected IV (1-5 mg metoprolol tartrate, Beloc, Schering) before the examination if the heart rate was greater than 75 beats per minute (bpm).


Figure 1
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  		Fig. 1A —Aortic valve (normal finding) appeared closed in two patients without aortic regurgitation during mid-to-late diastole. 67-year-old man with degenerative aortic stenosis. Tricuspid valve morphology and moderate valve calcifications (white) (Agatston calcium score [ACS]: 1997.1) were displayed by using volume-rendering technique (VRT) slab.

 


Figure 2
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  		Fig. 1B —Aortic valve (normal finding) appeared closed in two patients without aortic regurgitation during mid-to-late diastole. 75-year-old woman with degenerative aortic stenosis. Bicuspid valve morphology and moderate valve calcifications (white) (ACS: 2018.3) are shown by applying 3D VRT slab. VRT was preferred to show localization and extent of valve calcifications, which can provide interesting information to cardiac surgeons.

 


Figure 3
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  		Fig. 2A —47-year-old man with degenerative aortic stenosis. Concomitant moderate aortic regurgitation (grade 2+) is shown on cross-sectional transverse plane by applying multiplanar reformation (multiplanar reconstruction). Aortic valve leaflets did not close up tightly at diastole, and central triangular valvular leakage was revealed.

 


Figure 4
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  		Fig. 2B —47-year-old man with degenerative aortic stenosis. Central aortic regurgitation area (AR) was circled with digital caliper and calculated in cm2. Valve calcifications (arrow) might limit accurate quantification of aortic regurgitation area. RCC = right coronary cusp, LCC = left coronary cusp, NCC = noncoronary cusp.

 


Figure 5
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  		Fig. 3 —56-year-old woman with moderate aortic regurgitation (grade 2+) without valve calcifications. Note central triangular valvular leakage area.

 
Images were reconstructed with a smooth convolution kernel (B10 f), at an increment of 0.6, 1-mm effective slice thickness, image matrix 512 x 512, field of view 130-190 mm, and by using retrospective ECG gating at mid-to-end diastole (60-80% of R-R interval). Images were then transferred to a dedicated offline computer workstation (Leonardo, Siemens Medical Solutions). The aortic valve was reconstructed using multiplanar reformation (multiplanar reconstruction) and volume-rendering technique. Aortic valve leaflets were evaluated for whether a tight closure ("Mercedes-star" appearance) (Figs. 1A, 1B) or an area of central valvular leakage (Figs. 2A, 2B, 3, 4A, 4B, 5A, 5B, 6 and 7), suggesting aortic valve regurgitation, was noted by two independent observers. The central valvular leakage area was circled with a digital caliper and computed in cm2 (Fig. 2B).


Figure 6
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  		Fig. 4A —68-year-old man who had previous coronary bypass surgery and who underwent 16-MDCT angiography because of recurrent angina pectoris. Volume-rendering technique displays coronary bypass grafts: left internal thoracic artery and venous aortocoronary bypass graft (white arrow); right coronary artery with heavy calcifications and calcifying plaque at ascending aorta (black arrow) (white spots).

 

Figure 7
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  		Fig. 4B —68-year-old man who had previous coronary bypass surgery and who underwent 16-MDCT angiography because of recurrent angina pectoris. Moderate aortic regurgitation (grade 2+) with valve calcifications (white) was detected by applying multiplanar reconstruction. Note that aortic valve is prone to calcify in patients with coronary artery disease.

 

Figure 8
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  		Fig. 5A —57-year-old man with ascending aortic aneurysm. Ascending aortic aneurysm, which is frequently associated with aortic regurgitation, is shown with multiplanar reconstruction (left coronal oblique view).

 

Figure 9
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  		Fig. 5B —57-year-old man with ascending aortic aneurysm. Cross-sectional image of bicuspid valve shows central valvular leakage corresponding to moderate aortic regurgitation (grade 2+) without valve calcifications.

 

Figure 10
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  		Fig. 6 —48-year-old man who underwent 16-MDCT coronary angiography for suspected coronary artery disease. Mild aortic regurgitation (grade 1+) was incidental finding and appeared "spotlike," which may be easy to miss.

 

Figure 11
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  		Fig. 7 —66-year-old man with known degenerative aortic stenosis accompanied by severe valve calcifications (Agatston score: 10,107.2) and mild aortic regurgitation as assessed with transthoracic echocardiography. 16-MDCT could not detect aortic regurgitation because heavy valve calcifications located at valve leaflets margins prevented accurate display of central valvular leakage area.

 
Aortic valve calcifications were quantified on unenhanced 16-MDCT (collimation 16 x 1.5 mm, table feed 3.8 mm/rotation, gantry rotation 0.5 sec, 130 mAs, 120 kV, increment 3, 3-mm effective slice thickness, medium convolution kernel [B35 f], retrospective ECG gating at 60-80% of R-R interval) using dedicated coronary calcium scoring software (syngo, Leonardo, Siemens Medical Solutions).

Transthoracic Echocardiography
All measurements were performed using a standard sonography system (Sequoia 256, Acuson-Siemens) equipped with a 3.5/1.75 MHz transducer. Aortic valve regurgitation was assessed semiquantitatively by calculation of jet area/jet length, proximal jet width, and the pressure half-time method [7]. The severity of AR was classified as grade 0-3+ (mild, moderate, severe) [9]. Mean and maximum transvalvular pressure gradients were measured to assess whether aortic valve stenosis was present.

Statistical Analysis
Statistical analysis was performed using SPSS software (V8.0, SPSS). The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of 16-MDCT for identifying patients with AR were calculated. Interrater agreement was calculated by using weighted Cohen's kappa value. An unpaired Student's t test was used to determine the significance of differences in aortic valve calcification scores. The correlation between the severities of AR as measured by 16-MDCT and by TTE was determined by Spearman's rank correlation coefficient.


Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
The overall sensitivity of 16-MDCT for detection of patients with AR was 81% (95% confidence interval [CI], 68-89), the specificity was 91% (95% CI, 73-97), NPV was 70% (95% CI, 52-83), and PPV was 95% (95% CI, 83-98). Forty-eight of 71 patients had AR as determined by TTE. 16-MDCT correctly identified 39 of the 48 patients with AR.

The severity of AR was classified as moderate or severe (grade ≥ 1.5+) in 21 patients and as mild (grade ≤ 1.0+) in 27 patients with TTE. Twenty of the 21 patients who had AR of grade ≥ 1.5+ were detected with 16-MDCT (sensitivity 95% [95% CI, 77-99], specificity 96% [95% CI, 86-98], PPV 90% [95% CI, 72-97], and NPV 97% [95% CI, 89-99]). Sixteen-MDCT identified 19 of 27 patients who had mild AR grade ≤ 1+ as determined by TTE (sensitivity 70% [95% CI, 51-84], specificity 92% [95% CI, 75-97]). Interrater agreement was 0.96 ± 0.12 (weighted kappa value). Two patients were false-positive on 16-MDCT examination; both had valve calcifications.

Quantification of the central valvular leakage area (aortic regurgitation area [ARA]) by 16-MDCT was performed in 24 (50%) of the 48 patients. The mean ARA was 0.41 cm2 ± 0.47 (Table 1). In the remaining patients, quantification of ARA was not performed. In the opinion of both observers, circling ARA was judged as "probably inaccurate" because valve calcifications located at leaflets margins caused artifacts that projected into the ARA. The ARA as measured by 16-MDCT was correlated with the graduation of AR severity (grade 0-3+) by TTE (r = 0.95, p < 0.001, Spearman's rank correlation).


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  		TABLE 1: Patient Characteristics and Quantification of Aortic Valve Regurgitation Area by MDCT

 

A significant difference in aortic valve Agatston calcium score (ACS) (p = 0.004, unpaired Student's t test) was noted between the patients in whom quantification of ARA was possible and not possible (ACS: 1655.9 ± 1672 vs 3796.9 ± 2684).

The mean heart rate in our study population was 64 bpm ± 12.6 (minimum 44 bpm, maximum 78 bpm). Six patients had a right ventricular pacemaker; the other patients were in sinus rhythm.


Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
This study shows that 16-MDCT accurately identifies moderate and severe aortic regurgitation (grade ≥ 1.5+) in patients undergoing 16-MDCT coronary angiography, irrespective of the extent of valve calcifications. In contrast, the technique was less sensitive in detecting patients with mild AR (grade ≤ 1.0+), which might be explained by the fact that the spatial resolution of TTE is still superior to 16-MDCT. Furthermore, TTE is a technically different approach, based on Doppler flow analysis. However, the new 64-MDCT scanners provide higher spatial resolution than 16-MDCT and therefore improve aortic valve imaging. In addition, dedicated 4D cardiac postprocessing software is now available for 64-MDCT cardiac systems, facilitating the assessment of aortic valve dynamics during the cardiac cycle. The aortic valve is usually closed during diastole. Our data show in the presence of AR, 16-MDCT can detect a central valvular leakage area because the aortic valve leaflets do not close up tightly during diastole. This aortic valve regurgitation area could be quantified in 50% of our patients. However, quantification of ARA was evaluated as "probably inaccurate" and therefore was not performed in the remaining patients because of the presence of severe valve calcifications located at cusp margins, which caused blurring, and partial volume or beam-hardening artifacts that projected into the ARA.

Clinical Applications
Concomitant AR is frequently present in patients with ascending aortic aneurysm or degenerative aortic valve stenosis. Degenerative aortic stenosis is the second most common cardiovascular disease with a prevalence of 2-7% in Western European and North American people who are older than 65 years [10]. Coronary artery disease comorbidity in patients with degenerative aortic stenosis is relatively high because the pathomechanisms involved are similar and because coronary risk factors influence the progression of aortic stenosis [11, 12]. Therefore, radiologists and cardiologists interpreting coronary and ascending aortic 16-MDCT angiograms should evaluate the aortic valve simultaneously for concomitant AR.

Also, AR may develop secondarily either to rheumatic fever or to endocarditis, or may be congenital in patients with bicuspid valves. These patients may be young and may have a low pretest probability of coronary artery disease. Patients with severe AR require surgical treatment [10] and preoperative evaluation of coronary artery disease, which is currently routinely performed with cardiac catherization. Accordingly, these patients would be a target group for replacement of cardiac catheterization with 16- and 64-MDCT coronary angiography. However, better evaluation of the diagnostic performance of 16- and 64-MDCT coronary angiography for use with potential valve surgery patients can be done when results of ongoing clinical trials become available.

In contrast to cardiac catheterization, MDCT allows a detailed visualization of aortic valve morphology [13]. For example, the extent and localization of valve calcifications can be displayed, and differentiation between tricuspid and bicuspid valve shapes is feasible (Fig. 1A, 1B), which may provide interesting information that will help the cardiac surgeon select the surgical approach. Differentiation between bicuspid and tricuspid valve morphology may be difficult with TTE. Also, 16-MDCT allows detection of severe aortic regurgitation in a patient with acute ascending aortic dissection, which is important information to have before performing emergency surgical repair [14], supporting the use of 16- and 64-MDCT in patients with acute chest pain.

In conclusion, 16-MDCT provides a noninvasive, reliable imaging technique to identify moderate and severe aortic regurgitation of grade ≥ 1.5+ in patients undergoing 16-MDCT coronary angiography. Both 16- and 64-MDCT might also allow a new noninvasive, preoperative diagnostic approach in patients with planned cardiac surgery in the future.


References
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 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

  1. Hoffmann M, Shi H, Schmitz B, et al. Noninvasive coronary angiography with multislice computed tomography. JAMA2005; 293:2471 -2478[Abstract/Free Full Text]
  2. Nieman K, Cademartiri F, Lemos PA, et al. Reliable noninvasive coronary angiography using submillimeter multislice spiral computed tomography. Circulation 2002;106 : 2051-2054[Abstract/Free Full Text]
  3. Mollet NR, Cademartiri F, Krestin GP, et al. Improved diagnostic accuracy with 16-row multi-slice computed tomography coronary angiography. J Am Coll Cardiol 2005;45 : 128-132[Abstract/Free Full Text]
  4. Kuettner A, Kopp A, Schroeder S, et al. Diagnostic accuracy of multidetector computed angiography in patients with angiographically proven coronary artery disease. J Am Coll Cardiol2004; 43:831 -839[Abstract/Free Full Text]
  5. Nieman K, Pattynama PMT, Rensing BJ, et al. Evaluation of patients after coronary artery bypass surgery: angiographic assessment of grafts and coronary arteries. Radiology 2003;229 : 749-756[Abstract/Free Full Text]
  6. Schlosser T, Konorza T, Hunold P, et al. Noninvasive visualization of coronary artery bypass grafts using 16-detector row computed tomography. J Am Coll Cardiol 2004;44 : 1224-1229[Abstract/Free Full Text]
  7. Flohr T, Bruder H, Stierstorfer K, et al. New technical developments in multislice CT.2. Sub-millimeter 16-slice scanning and increased gantry rotation speed for cardiac imaging. Rofo 2002; 174:1023 -1027
  8. Hunold P, Vogt FM, Schmermund A, et al. Radiation exposure during cardiac CT: effective doses at multi-detector row CT and electron-beam CT. Radiology 2003;226 : 145-152[Abstract/Free Full Text]
  9. Buck T, Plicht B, Wenzel RR, Hunold P, Erbel R. Echocardiography flow quantification for determining the severity of heart valve insufficiency [in German]. Herz 2002;27 : 254-268[Medline]
  10. Bonow R, Carabello B, de Leon AC Jr, et al. Guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Patients with Valvular Heart Disease). Circulation 1998;98 : 1949-1984[Free Full Text]
  11. Stewart BF, Siscovick D, Lind BK, et al. Clinical factors with calcific aortic valve disease. J Am Coll Cardiol1997; 29:630 -634[Abstract]
  12. Pohle K, Maffert R, Ropers D, et al. Progression of aortic valve calcification: association with coronary atherosclerosis and cardiovascular risk factors. Circulation 2001;104 : 1927-1932[Abstract/Free Full Text]
  13. Willmann JK, Weishaupt D, Lachat M, et al. Electrocardiographically gated multi-detector CT for assessment of valvular morphology and calcifications in aortic stenosis. Radiology2002; 225:120 -128[Abstract/Free Full Text]
  14. Feuchtner GM, Schachner T, Friedrich G, et al. Acute aortic dissection with coronary ostium involvement and aortic valve regurgitation: three-dimensional visualization with multislice computed tomography. J Thorac Cardiovasc Surg 2005;130 : 587-588[Free Full Text]

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