Between April 2007 and October 2009 we prospectively enrolled 100 patients who underwent CT for evaluation of coronary artery disease. For bi-ventricular volume assessment, patients were also scheduled for an MR within one week after CT. We adhered to the exclusion criteria reported in literature [³³–³⁵]: for CT, we excluded patients with a) an heart rate >65 bpm (beats per minute) not responding to beta-blockers; b) atrial fibrillation and concomitant high ventricular response; c) known reactions to contrast medium; d) renal insufficiency (creatinine > 1.5 mg/dL); e) impaired pulmonary function (unable to perform a 12-s breath-hold); for MR, we excluded patients with a) claustrophobia; b) pacemaker/other non MR compatible devices [³⁴]. Twenty-one patients were excluded because of unsuitability to undergo MR (11 for claustrophobia; 3 for increasing dyspnoea during acquisition; 4 for ICD; 2 for pacemaker; 1 for a Starr-Edwards mitral valve); within our cohort no patient needed exclusion from CT. Complete CT and MR datasets could be acquired in 79 patients (mean age: 58; 46 male) (Table 1).

Written informed consent was obtained from all patients, and the study was approved by the Ethics Review Board of our hospital.

Upon arrival, blood pressure and heart rate (HR) were measured and 5–20 mg of intra-venous atenolol were administered if the HR exceeded 65 bpm, in order to reach a HR below 65 bpm. Twenty-five patients required treatment with β-blockers before CT; the others had no necessity (40 patients) or had contraindications (14 patients). ECG-gated 64-slice spiral CT (Sensation 64, Siemens, Forchheim, Germany) was performed without ECG-triggered tube modulation: detector collimation: 32 × 0.6 mm, Z-axis focal spot alternation resulting in simultaneous acquisition of 64 slices; gantry rotation: 330 ms; effective temporal resolution 165 ms; table feed per rotation: 3.84 mm; tube voltage 120 kVp; tube current 800–950 mAs; direction in which data acquisition proceeded : cranio-caudal. Just before the CT data acquisition 0.3 mg of sublingual nitroglycerin was administered in the absence of contraindications. For contrast enhancement, 110 mL of contrast medium (Iomeprol, Iomeron 400, Bracco, Milan, Italy) was administered intravenously at 5 mL/s (2 g iodine/s) flow rate, followed by 40 mL of saline chaser at same flow rate [¹⁷]. A bolus tracking technique for contrast bolus arrival and data acquisition synchronisation was used. The anatomical coverage extended from the tracheal bifurcation to the diaphragm. In patients who previously underwent bypass graft surgery, the start was positioned just at clavicle level to include internal mammary artery origin. Using a partial reconstruction algorithm (requiring 180° of projections) thin-slice images were reconstructed for the coronary evaluation. In addition functional MPR (multiplanar reconstruction) images were reconstructed using dedicated CT software (Syngo CT-2007A; Siemens, Forchheim, Germany). Using the standard cardiac planes for orientation, 8-mm MPR thick with a 2-mm gap images of the ventricles, extending from the base to the apex, were reconstructed throughout the cardiac cycle at 5% intervals (Fig. 1).

MR was performed at 1.5T (Achieva, Philips Medical Systems, Best, The Netherlands) with the following acquisition parameters: maximum gradient strength of 66 mT/m, maximum slew rate 180 mT/m × ms, maximum gradient strength during Cine-Cardiac MR acquisition 33 mT/m, and maximum slew rate during Cine-Cardiac MR acquisition 180 mT/m × ms. Five-element synergy cardiac coil and vector electrocardiography were used for signal detection and cardiac gating. One experienced operator (4 years’ Cardiac MR) performed all examinations. After initial scout imaging and reference acquisition, short-axis cine images covering the entire left and right ventricles from base to apex were acquired during repeated end-expiratory breath holds using a 2D b-SSFP (2D-cine) sequence (Fig. 1). All acquisitions were performed holding the breath at end expiration to avoid slice misalignment [³⁶, ³⁷]. The imaging parameters for 2D-cine were as follows: TR (repertition time) 3.1 ms; TE (echo time) 1.53 ms; flip angle 60°; bandwidth 1249.7 HZ/pixel; in plane resolution 2 × 2.3 mm; slice thickness 8 mm; slice gap 2 mm; temporal resolution 32 ± 6 ms (depending on heart rate); cardiac phase 30; SENSE: off; half scan: Yes.

A total of 158 short axis datasets, 79 obtained by MR acquisition and 79 by CT multiphasic reconstruction, were transferred to a dedicated workstation (Syngo MMWP – Siemens, Forchheim, Germany) equipped with ARGUS Va60c analysis software (ARGUS, Va60c, Siemens, Forchheim, Germany), which is able to process DICOM images from images obtained using different techniques. One experienced observer (>5 years in Cardiac MR and CT) blindly and randomly analyzed all MR and CT images to measure the end-diastolic volume (EDV) and end-systolic volume (ESV), and calculate the stroke volume (SV) and ejection fraction (EF) of left and right ventricle, as well as the end-diastolic wall mass (ED Wall Mass) on the left ventricle. [³⁸]. Images acquired at the time of the R-wave of the ECG were considered to represent end-diastole (ED), while images showing the smallest detectable left ventricular cavity were considered as end-systolic (ES) [¹⁸]. Endocardial and epicardial contours were manually traced on the end-diastolic SAX images. Endocardial borders were automatically “propagated” on end-systolic phase images, and manually corrected when deemed necessary. Papillary muscles and trabeculations of the LV and RV cavities were included in the LV and RV cavity volumes as previously described [³⁹–⁴¹]. The most apical section with visible cavity was considered as apex and the most basal section with at least 50% surrounding myocardium was regarded as base [²³]. EDV and ESV were calculated without geometric assumptions, using the Simpson’s rule. All parameters were indexed for body surface area (BSA). For calculation of intra-observer and inter-observer variability tracing of myocardial borders was repeated after at least 1 month by the same investigator, and in addition by a second investigator (4 years’ Cardiac CT and Cardiac MR), who was unaware of previous results.

We hypothesized that CT can measure right and left ventricular volumes, and left myocardial mass with acceptable accuracy and reproducibility; thus we directly compared right and left ventricular measurements obtained by CT with the results of MR as the currently accepted reference standard for cardiac chamber volume measurement. For data analysis we used commercially available software (MedCalc v9.2.1.0, Mariakerke, Belgium). The correlation between CT and MR was tested by two-variable linear regression analysis including calculation of Pearson’s correlation coefficient. To further examine the agreement between CT and MRI , Bland-Altman method was used [⁴²] (Fig. 2). The agreement between CT and MR was determined as the mean difference, the standard error of estimation for the mean difference, the 95% confidence interval of the mean difference, and the limits of agreement for both investigations (mean ± SD). Differences were investigated with Student’s T test (2 tails) for paired samples and a p < 0.05 was considered as significant. The comparison of the intra-observer and inter-observer variability between CT and MR was assessed by calculating the coefficient of variability equal to the standard deviation of the difference between two measurements over the mean of the two measurements and expressed as percentage [¹⁶, ⁴³]. Three patient subgroups were created according to EF value: <35%, 35% ≤ EF ≤ 50%, >50% and analyzed with Student’s T Test, Pearson’s correlation and Bland Altman analysis.

Although the exact radiation dose was not evaluated in this population, it should be mentioned that ECG-gated 64-slice CT without ECG-triggered tube modulation is associated with an exposure between 12–18mSv [⁴⁵–⁴⁷]. More modern CT equipment implements different techniques able to acquire datasets useful for coronary tree and LV and RV function evaluation at lower radiation dose [⁴⁸, ⁴⁹].

Using MR as reference, we demonstrated that ECG-gated cardiac CT accurately assesses both left and right ventricular function, with excellent reproducibility of the functional parameters. Thereby it may be regarded as a reliable alternative to echocardiography and magnetic resonance imaging taking into account the potential risks of radiation and iodinated contrast medium.

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No conflicts of interest to disclose from all Authors. The paper is original and not submitted elsewhere.

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The Table shows demographics of the study population

Abbreviations: SD Standard Deviation, BSA Body Surface Area (according to Mosteller’s formula)

The Table shows global ventricular parameters (Right and Left Ventricle) calculated with MR and CT. Parameters are expressed as mean ± SD

Abbreviations: MR Magnetic Resonance, CT Computed Tomography, EDV End Diastolic Volume, ESV End Systolic Volume, SV Stroke Volume, EF Ejection Fraction, ED wall mass End Diastolic wall mass, p-Value Student’s paired test, r-value Pearson’s correlation, 95% LA Limits of agreement with Bland-Altman analysis (mean in parenthesis)

The Table shows the Coefficient of Variation of ventricular parameters calculated with Deming Regression. Parameters are expressed as percentage variability

Abbreviations: MR Magnetic Resonance, CT Computed Tomography, EDV End Diastolic Volume, ESV End Systolic Volume, SV Stroke Volume, EF Ejection Fraction, ED wall mass End Diastolic wall mass, p-Value Student’s paired test

The Table shows the comparison of Ejection Fraction (Right and Left Ventricle) calculated with MR and CT for the entire population and for ventricular functional subgroups (EF < 35%; 35% ≤ EF ≤ 50%; EF > 50%). Parameters are expressed as mean ± SD

Abbreviations: MR Magnetic Resonance, CT Computed Tomography, n. number of patients, EF Ejection Fraction, p-Value Student’s paired test, r-value Pearson’s correlation, 95% LA Limits of agreement with Bland-Altman analysis (mean in parenthesis)