Multidetector-Row CT Assessmentof Left-Ventricular Function 18

CHAPTER 18/ MDCT ASSESSMENT OF LEFT-VENTRICULAR FUNCTION 183

183

Multidetector-Row CT Assessment of Left-Ventricular Function

K AI U WE J UERGENS , MD AND R OMAN F ISCHBACH , MD

From: Contemporary Cardiology: CT of the Heart:

Principles and Applications

Edited by: U. Joseph Schoepf © Humana Press, Inc., Totowa, NJ

INTRODUCTION

For the diagnosis, disease stratification, treatment planning, and prognosis of different cardiac diseases clinically present- ing with myocardial dysfunction and regional or global ischemia, respectively, the accurate and reproducible determin- ation of left-ventricular myocardial function is fundamental.

Heart failure afflicts about 4.5 to 5 million people in the United States, with more than 500,000 new cases developing each year.

Clinical assessment with regard to left-ventricular function is generally difficult; although an entirely normal electrocardio- gram (ECG) provides a close correlation to normal systolic function, electrographical findings are nonspecific. The ideal imaging modality to determine left-ventricular function in a clinical setting would be noninvasive, accurate, reproducible, easily available, as well as cost and time effective (1–3).

The analysis of left-ventricular myocardial function includes the determination of regional and global function characteris- tics. Regional function parameters are myocardial wall thick- ness and wall thickening, calculated as end-diastolic and end-systolic wall thickness, systolic wall thickening, and per- cent systolic wall thickening. Clinical information on global left-ventricular function are determined from measurements of diastolic and systolic left-ventricular volumes and consecu- tively calculated ejection fraction, stroke volume, and cardiac output. With regard to reproducibility and accuracy of global functional parameters, an imaging modality is only as good as its measurements of left-ventricular volumes.

ESTABLISHED TECHNIQUES FOR ASSESSING LEFT-VENTRICULAR FUNCTION

Various noninvasive imaging modalities (such as echo- cardiography, radionuclide ventriculography, gated perfusion single photon emission computed tomography [SPECT], elec- tron-beam computed tomography [EBCT], and cardiac mag- netic resonance imaging [MRI]) and invasive techniques (such as cine ventriculography [CVG]) are in use for the determina- tion of regional and global left-ventricular function.

Transthoracic echocardiography is a widely available imag- ing modality, relatively cheap and mobile; however, image acquisition is acoustic-window and operator dependent. Owing to geometric assumptions of the left-ventricular shape, accu- racy in regards to quantitative assessment of left-ventricular function is hampered in remodeled hearts with complex irregu- lar shape changes. Good visualization of the entire endocardial border cannot always be provided using conventional 2D echocardiography, resulting in a high amount of subjectivity and dependency on the operator’s clinical experience. Thus, reliable measurement of myocardial thickness and thickening is frequently elusive. Three-dimensional echocardiography has improved its clinical impact; however, dependency of acoustic windows and clinical practicability have to be evaluated in further studies. Analysis of left-ventricular volume-time curves by real-time 3D echocardiography provides quantitative data on global left-ventricular function, such as filling rates (4).

CVG while performing coronary catheter angiography is currently a clinically accepted standard for the assessment of cardiac volumes and function. However, this method is inva- sive and is limited as a result of geometric assumptions made from projection images.

Radionuclide ventriculography is commonly used to mea- sure cardiac function in terms of left-ventricular ejection frac- tion; however, it is rarely performed clinically, because it is hampered by limited temporal and spatial resolution, and prepa- ration and scanning times are relatively prolonged (5). Gated perfusion SPECT is not used to measure ventricular function alone, although it enables 3D assessment of cardiac function and is especially useful when perfusion needs to be assessed with a high reproducibility. Its diagnostic accuracy might be limited both in small and large ventricles due to limited spatial resolution. Owing to very low counts, it is difficult to define ventricular borders in left-ventricular areas with circumscript thinning as a result of transmural infarction. In both nuclear techniques, the need for repeated radionuclide doses in sequen- tial studies is problematic due to radiation exposure. Using

99m

Tc-tetrofosmin, the dose equivalent for myocardium and a blood pool marker is about 8 × 10

mSv per 100 MBq. In a clinical setting, about 750 to 900 MBq

Tc-tetrofosmin are commonly used to perform a first-pass radionuclide ventricu- lography.

18

Table 1

Left-Ventricular (LV) Parameters (mean ± 1 SD) With 95% Confidence Interval (1.96 SD) in Parentheses ^a

ALL Males Females

(N = 75) (N = 47) (N = 28)

LV end-diastolic volumes [mL] 121 ± 34 (55–187) 136 ± 30 (77–195) 96 ± 23 (52–141) LV end-diastolic volumes BSA [mL/m

] 66 ± 12 (44–89) 69 ± 11 (47–92) 61 ± 10 (41–81) LV end-systolic volumes [mL] 40 ± 14 (13–67) 45 ± 14 (19–72) 32 ± 9 (13–51) LV ejection fraction [%] 67 ± 5 (57–78) 67 ± 5 (56–78) 67 ± 5 (56–78)

LV stroke volume [mL] 82 ± 23 (36–127) 92 ± 21 (51–83) 65 ± 16 (33–97)

a

Derived from reference method cardiovascular magnetic resonance imaging. BSA, body surface area; SD, standard deviation. N = 75. Modified from ref. 11.

EBCT scanners providing a temporal resolution down to 50–100 ms have been successfully used for noninvasive coro- nary calcium measurements, coronary arteriography, and determination of left-ventricular (LV) mass and function data.

However, these systems are costly, and the limited number of scanners available restricts access to this modality (6,7). Pro- spectively ECG-triggered sequential single-slice scanning is performed with a selected delay from the preceding R peak of the ECG. This prospective triggering technique renders the images vulnerable to sudden changes in heart rate or cardiac rhythm. The fixed setup of an EBCT scanner impairs assessing LV functional parameters in the anatomically true short-axis orientation, as it is applied in echocardiography and cardiac MRI.

In comparison to other noninvasive imaging techniques, cardiac MRI is now widely accepted as the reference standard of noninvasive assessment of cardiac function, being accurate and reproducible in normal and also in abnormal ventricles using conventional breath-hold turbo-gradient echo sequences (TGrE) as well as newly developed steady-state free precession (SSFP) cine sequences (8–10). Cardiac MRI provides an excel- lent temporal and spatial resolution, with image acquisition in any desired plane (e.g., in vertical and horizontal long-axis and short-axis views). Image acquisition can be performed rapidly to allow visual and qualitative assessment of global and regional left-ventricular function. A synopsis of global left-ventricular functional parameters in healthy volunteers (11) as determined by cardiac MRI is given in Table 1.

ASSESSMENT OF LEFT-VENTRICULAR FUNCTION USING CT

Application of conventional CT to cardiac imaging has long been limited by insufficient temporal resolution as a result of slow gantry rotation, and long total acquisition time resulting from slow volume coverage with single-slice imaging. Analy- sis of cardiac function has been possible only in experimental setups and was restricted to a transaxial slice orientation (12,13). Cardiac imaging using conventional single-slice CT scanners had become available with the introduction of sub- second rotation in 1994. Initial promising results were achieved using prospective ECG-triggering technique combined with a possible temporal resolution of 500 ms. As in EBCT, prospec- tive ECG-triggering techniques enable determination of volu- metric data of the heart from sequential scans, which are started following a predefined delay to the onset or the R waves of the

patient’s ECG. A major drawback of prospectively ECG-trig- gered image acquisition, however, is its vulnerability to cardiac arrhythmia or changes in heart rate.

Continuous imaging of the heart volume with spiral tech- nique and ECG-synchronized image reconstruction was severely hampered because of limited volume coverage in the patient-longitudinal (z) axis when only one detector line was available. In contrast, multidetector spiral CT technique enables scanning of larger anatomical volumes at a given scan time or smaller volumes at a narrower collimation, resulting in a higher axial resolution. Thus, high-quality data sets for 3D postpro- cessing are provided. The entire volume of the heart can be scanned within a single breath-hold. Motion of the heart can be virtually frozen using retrospective ECG-gating technique, when the ECG signal of the patient is recorded simultaneously during spiral CT data acquisition. The method of retrospective ECG gating enables greater robustness with regard to arrhyth- mia, because prospective estimation of the heart rate is not needed for the trigger’s placement (14). In the clinical setting, left-ventricular function information can be derived from multidetector-row CT (MDCT) coronary angiography data sets. From axial thin-section CT spiral data sets acquired dur- ing the entire cardiac cycle, images at diastolic and systolic window can be subsequently reconstructed using retrospec- tive ECG-gating technique (see “Data Acquisition and Image Reconstruction” below).

DETERMINATION OF LEFT-VENTRICULAR VOLUMETRIC DATA

For clinical and research purposes, left-ventricular volum-

etric data are determined using different anatomical and geo-

metric models. The standard approaches for reliable and

reproducible volumetrics are the area-length method based on

the long-axis view as well as the Simpson’s method applied to

contiguous short-axis reformations (Fig. 1). For reproducible

assessment of volumetric data, the imaging of the left ven-

tricle along to the cardiac imaging axes is advantageous,

because the body axes—i.e., transverse, sagittal, and coronal

planes (Figs. 2–4)—are not perpendicular to the left-ventricu-

lar cavity or the myocardial wall, resulting in an overestimation

of true left-ventricular dimensions owing to partial-volume

effects and obliqueness of those axes. High z-axis resolution

nearly approaching isotropic voxels, provided by MDCT tech-

nique, enables multiplanar reformations (MPRs) from primary

axial image reconstructions—in particular, the left-ventricular

CHAPTER 18/ MDCT ASSESSMENT OF LEFT-VENTRICULAR FUNCTION 185

Fig. 1. Diagram showing two different geometric models for determination of left-ventricular volumetric data: the standard approaches for reliable and reproducible volumetric are the Simpson’s method applied to contiguous short-axis reformations using 3D reconstruction (A) as well as the area-length method based on the long-axis view of the heart using the biplane ellipsoid model (B). A = cross-sectional area within endocardial borders determined from one section (modified from 9).

long axis and the short-axis plane: starting with axial recon- structions, a vertical long-axis plane is obtained connecting the left-ventricular apex and the middle of the atrioventricular junc- tion. A further plane connecting the left-ventricular apex and the middle of the mitral valve ring is chosen, resulting in a horizontal long-axis plane. Perpendicular to the horizontal long axis, the stack of double-oblique short-axis images are orien- tated by an inclination parallel to the mitral-valve ring. Second- ary MPRs in horizontal and vertical long-axis and true short-axis orientation, respectively, can be performed from diastolic and systolic reconstructions, enabling determination of left-ventricular end-diastolic and end-systolic volumes (Figs. 5 and 6). Consecutively, the calculation of left-ventricu- lar ejection fraction and stroke volume is feasible as follows:

Fig. 2. Multidetector CT postprocessing and generation of multiplanar reformations in an anatomically optimized vertical long-axis view.

C.t., chordae terdinae; MV, mitral valve; PPM, posterior papillary muscle.

Fig. 3. Multidetector CT postprocessing and generation of multiplanar reformations in an anatomically optimized horizontal long-axis view.

IVS, intraventricular septum; LA, left atrium; MV, mitral valve; RCA, right coronary artery; T.s., Trabecular septomarginalia.

Area-length method. From a long-axis view, the area A within traced endocardial contours and the length L from the left-ventricular apex to the level of mitral valve ring are used to calculate the LV volume (V

) according to equation 1:

V

= (8/3) × A

/πL (1)

Fig. 4. (A) The standard sagittal, coronal, and axial orientation of multiplanar reformations (MPR) as provided by standard postprocessing

software. Based on those standard angulations, MPR in the long-axis view and four-chamber view can be generated, resulting in a true short-

axis orientation (B). With regard to functional analysis, a stack of double contiguous short-axis-orientated sections (thickness 8 mm without

any intersection gap) is acquired.

CHAPTER 18/ MDCT ASSESSMENT OF LEFT-VENTRICULAR FUNCTION 187

Fig. 6. Endocardial contours were manually traced using standard planimetric software implemented in the workstation. Midventricular short- axis multidetector-row CT (MDCT) images in end diastole (A) and end systole (B) showing the manually traced endocardial borders and the respective cross-sectional areas (A: 17.61 cm

, B: 8.55 cm

) in a patient with arrhythmogenic right-ventricular cardiomyopathy. Coronary artery disease was ruled out using MDCT coronary angiography; global left-ventricular (LV) function was normal (LV-ejection fraction 72.9%). Calculation of diastolic and systolic left-ventricular volumes using Simpson’s method based on the short-axis reformations.

Fig. 5. Ten to eighteen sections are used to encompass the entire left ventricle from base to apex.

Simpson’s method. Endocardial contours of all short-axis images showing left-ventricular cavity are traced with papil- lary muscles being included into the left-ventricular cavity to calculate the cross-sectional area A of each section. Left-ven- tricular volumes (V

) are calculated by adding all measured cross-sectional areas A

multiplied by the intersection thick- ness S:

V

= ΣA

× S (2)

Left-ventricular ejection fraction (LV-EF) is calculated for both, long-axis and short-axis reformations, from end-diastolic

(LV-EDV) and end-systolic (LV-ESV) volumes according to equation 3

LV-EF = [(LV

– LV

)/LV

] × 100% (3)

PRACTICAL GUIDE TO FUNCTIONAL MDCT—

SCAN PROTOCOL, IMAGE ACQUISITION, AND DATA ANALYSIS

DATA ACQUISITION AND IMAGE RECONSTRUCTION

In initial studies, left-ventricular function data have been

determined from MDCT coronary angiography studies using

standard technique. The preparation and carrying-out of the MDCT studies are performed according to the manufacturer’s recommendations. For optimal contrast bolus timing, the use of a bolus tracking technique is not necessary; however, a good contrast between endocardium and left-ventricular cavity is mandatory, enabling optimized delineation of endocardial con- tours. Following CT data acquisition, retrospectively ECG- gated image reconstruction in axial orientation is performed using standard reconstruction parameters in overlapping slices (increment < slice thickness) in set increments.

In order to calculate volumetric data, the maximal systolic constriction and diastolic relaxation phase of the left ventricle are identified by performing an axial image test series at midventricular level in 5% steps through the entire RR interval.

It is recommended that axial images show the anterior left- ventricular papillary muscles as well as the anterior and poste- rior leaflet of the mitral valve (Fig. 7). End-diastolic and end-systolic phase are identified electrocardiographically and controlled visually as the images showing the largest and small- est left-ventricular cavity area, respectively. The reconstruc- tion windows determined in this way finally are used for diastolic and systolic image calculation. According to a current study, a mean reconstruction window for diastolic image series was 83.1 ± 4.1% (range 75 to 90) of the RR interval, whereas systolic image reconstructions from MDCT data sets were per- formed at 23.1 ± 3.8% (range 20 to 35) of the RR interval (15).

From axial image reconstructions, short-axis orientated MPRs are created for diastolic and systolic image series. To encompass the entire left ventricle from the base of the heart to its apex, usually ten to eighteen sections of short-axis-orien- tated MPRs are needed. In principle, any section thickness is possible. A section thickness of 8 mm using no intersection gap seems to be sufficient, according to experiences from cardiac MRI (Fig. 5 and 6).

DATA ANALYSIS OF LEFT-VENTRICULAR VOLUMETRY AND FUNCTION

Left-ventricular volumetric analysis can be performed from MPRs orientated to left-ventricular long axis and short axis, respectively, using standard 3D postprocessing software as provided by several manufacturers. Recently, dedicated analysis software enabling semiautomated contour detection might has been developed as an alternative for clinical and research purposes.

DATA ANALYSIS USING STANDARD 3D SOFTWARE Diastolic and systolic left-ventricular volumes can be calcu- lated using standard planimetric software provided by the dif- ferent manufacturers according to the area-length method based on the long-axis view as well as to Simpson’s method applied to contiguous short-axis reformations (see “Assessment of Left Ventricular Function Using CT” above). The tracing of left- ventricular endocardial contours as well as the determination of left-ventricular area and length in the long-axis view are done using standard software tools with manual interaction. As in cardiac MRI, papillary muscles and endocardial trabeculae should be included in the left-ventricular cavity and excluded from the left-ventricular volume.

DATA ANALYSIS USING DEDICATED ANALYSIS SOFTWARE

Alternatively, left-ventricular volumes can be determined by analysis software adapted from cardiac MRI, which has been validated in research and clinical studies for the past decade. Following data acquisition and postprocessing, MPRs are performed in short-axis orientation. For diastolic and sys- tolic MPRs, basal and apical sections are visually identified and manually marked. To ensure reproducible data analysis, the first short-axis orientated section should be placed at the heart’s base, covering the most basal portion of the left ven- tricle just forward of the atrioventricular ring. Endocardial borders are traced semiautomatically in both image series, start- ing with a software-generated ellipsoid or circular figure placed in the middle of the left-ventricular cavity. Contours are visu- ally reviewed for correctness and, if necessary, are manually adjusted to endocardial contours.

ACCURACY AND REPRODUCIBILITY OF MDCT ASSESSMENT OF LEFT-VENTRICULAR FUNCTION

So far, only initial results have been reported from studies with small numbers of patients evaluating left-ventricular vol- ume and function assessment from MDCT in comparison to such established techniques as CVG (16–19), echocardio- graphy (20), and cardiac MRI (15,21–23).

As has been demonstrated for cardiac MRI, an early study comparing MDCT and biplane CVG determination of left- ventricular ejection fraction found a better correlation if Simpson’s method on short-axis reformations was used in comparison to the area-length method. Regions with previous myocardial infarction could clearly be delineated, showing a thinned LV wall and reduced or missing systolic myocardial wall thickening (16). Those results were confirmed by others (17–19), showing that 3D data assessed from retrospectively ECG-gated MDCT studies enable calculation of left-ventricu- lar volumes to estimate systolic function. All authors consis- tently found an overestimation of left-ventricular end-systolic volumes, resulting in underestimation of left-ventricular ejec- tion fraction in MDCT. In comparison to transthoracic echocardiography, no significant differences in left-ventricu- lar volumes and ejection fraction were detected from MDCT in patients with both ischemic and nonischemic cardiomyopa- thies (20). Measurements of end-diastolic and end-systolic volumes as determined by MDCT revealed a close correlation to respective cardiac MRI measurements (Figs. 8–11, Table 2).

Acceptable limits of agreement between the two modalities were found, demonstrating a mean difference below 1% and 1.5 mL regarding determination of left-ventricular ejection fraction and stroke volume (Fig. 12), respectively (16,22,23).

The use of MDCT for the analysis of global left-ventricular

function has been limited by the lack of standardized analysis

software in clinical practice. Semi-automated or automated

methods of border detection have been developed in such car-

diac imaging techniques as echocardiography or monoplane

and biplane CVG (24). An initial study demonstrated that evalu-

ation of MDCT data sets lasted 10–15 min using analysis soft-

ware to perform semi-automated contour detection. Although

CHAPTER 18/ MDCT ASSESSMENT OF LEFT-VENTRICULAR FUNCTION 189

189

Fig. 7. Screenshots acquired from the scanner’s main workstation (Navigator

) illustrating an axial-image-orientated test series in 5% steps ( A–J) through the entire RR interval at midventricular level. Axial sections show the anterior left ventricular papillary muscles as well as the anterior and posterior leaflet of the mitral valve. End-diastolic and end-systolic phase were identified electrocardiographically and controlled visually as the images showing the largest and smallest left-ventricula r cavity area, respectively. The corresponding reconstruction window was used for image calculation.

Fig. 8. Short-axis reformations comparing four-slice multidetector-row CT (MDCT) technology (A and B) to cardiac magnetic resonance imaging (MRI) (C and D) using conventional turbo gradient-echo sequences. (A) MDCT diastole; (B) MDCT systole (minor stair step artifacts resulting from a mean heart rate of 69 beats per minute); (C) MRI diastole; (D) MRI systole. Left-ventricular ejection fraction was 51.8% as determined from MDCT study in comparison to 57.9% as calculated from cine MRI.

Fig. 9. Short-axis reformations comparing four-slice multidetector-row CT (MDCT) technology and cardiac magnetic resonance imaging (MRI) using steady-state free precession (SSFP) cine sequences. Diastolic (A,C) and systolic (B,D) short-axis reformations from MDCT (A,B) and SSFP cine magnetic resonance imaging (MRI: C,D) studies from a 58-yr-old female patient with one-vessel coronary artery disease.

Normal dimensions of both ventricles and myocardial wall thickness, normal global left-ventricular function (left-ventricular ejection fraction

= 67.5% MDCT vs 67.6% MRI).

CHAPTER 18/ MDCT ASSESSMENT OF LEFT-VENTRICULAR FUNCTION 191

endocardial left-ventricular contours had to be manually cor- rected in some cases, there was not a relevant difference in comparison to cardiac MRI data sets, with a mean analysis time of approx 10 min. Thus, in selected patients evaluated for coro- nary artery disease, semiautomated analysis software enabled reliable left-ventricular volumetric measurements and func- tion analysis from MDCT data sets (Table 3) in comparison to SSFP cardiac MRI (15).

With regard to left-ventricular end-diastolic and end-sys- tolic volumes as well as ejection fraction as determined by MDCT studies, an inter-observer variability between 6 and 8%

was reported (16,22).

It has been generally accepted that a temporal resolution of 50 ms—achievable by established techniques as CVG, nuclear techniques, EBCT, and cardiac MRI—is mandatory for a repro- ducible evaluation of global left-ventricular function. Currently available MDCT techniques achieve a temporal resolution down to 105 ms, depending on the patient’s heart rate. How- ever, initial studies published by different investigators suggest that left-ventricular volumetric and functional evaluation by MDCT gives reliable results in comparison to reference modali- ties. A current study compared data of patients with a mean heart rate below and above 65/min, respectively, revealing no significant differences with regards to reliability of volumetric measurements (15) by MDCT (Table 4).

Fig. 10. Diastolic (A,C) and systolic (B,D) short-axis reformations from multidetector-row CT (MDCT) (A,B) and steady-state free precession cardiac magnetic resonance imaging MRI (C,D) studies obtained in a 72-yr-old male patient with three-vessel coronary artery disease who had experienced previous inferior myocardial infarction. Hypokinetic infero-septal and akinetic inferior wall of left ventricle can be clearly identified (white arrow; left-ventricular ejection fraction = 64.1% MDCT vs 62.9% MRI).

Fig. 11. Systolic short-axis reformation from sixteen-slice

multidetector CT at midventricular level from a 72-yr-old man with

a history of three-vessel coronary artery disease having undergone

bypass surgery (white arrow indicates a tiny vascular clip from a

bypass to the left descending coronary artery). As a result of recurrent

myocardial infarction the multiplanar reformation in the short-axis

demonstrates an absent regional contraction of left-ventricular myo-

cardium in the lateral and inferior wall of left-ventricular myocar-

dium including the posterior papillary muscles (dark arrows). APM,

anterior papillary muscle; PPM, posterior papillary muscle.

Table 2

Comparison of Left-Ventricular Volumetric and Functional Parameters As Determined From MDCT of the Heart in Comparison to CVG and MRI Using TGrE and SSFP Cine Sequences

Modality LV-EF:

compared MDCT vs

Reference N to MDCT LV-EDV LV-ESV LV-EF other modality

Juergens et al. (22) 28 TGrE-MRI 0.92 0.90 0.90 –7.9 ± 5.6 %

Wintersperger et al. (17) 25 CVG 0.59 0.88 0.82 –17 ± 9 %

Hundt et al. (19) 30 CVG 0.72 0.88 0.76 –13.7 ± 11 %

Erhard et al. (27) 7 SSFP-MRI 0.93 0.95 0.83 –3.8 ± 9.4 %

Mahnken et al. (23) 16 SSFP-MRI 0.99 0.99 0.98 –0.9 ± 3.6 %

Juergens et al. (15) 30 SSFP-MRI 0.93 0.94 0.89 –0.25 ± 4.9 %

CVG, cine ventriculography; MDCT, multidetector-row computed tomography; MRI, magnetic resonance imaging; SSFP, steady-state free precession; TGrE, Turbo gradient-echo.

Fig. 12. Bland-Altman plots of left-ventricular end-diastolic volume (LVEDV) (A), left-ventricular end-systolic volume (LVESV) (B), and left-ventricular ejection fraction (LVEF) (C), showing the rela- tion between differences and means between multidetector-row CT (MDCT) and cine steady-state free precession magnetic resonance imaging (MRI) for each parameter. The difference (y axis) between each pair ([mean MDCT] – [mean MRI]) is plotted against the average value (x axis) of the same pair ([(mean MDCT) + (mean MRI)]/2). (A–

C: solid lines = mean value of differences; short dotted lines = mean value of differences ± 2 standard deviation.)

FURTHER DEVELOPMENTS

Progress concerning a more accurate determination of end- systolic frames, and possibly analysis of regional myocardial function, can be expected from MDCT systems with reduced gantry rotation time (below 500 ms) and a concomitant increase in temporal resolution (down to 105 ms). As a result of physical

limitations, however, a further significant increase in tempo- ral resolution may be realized only by separating physiological and physical acquisition time. Multisegment-reconstruction algorithms have become available for MDCT that process data from several gantry rotations and can reduce the temporal reso- lution down to 70–90 ms (25,26). Initial results, however, sug- gest that the resulting decrease in spatial resolution limits left-ventricular function analysis by multisegment-algorithms in comparison to cardiac MRI.

MDCT VS CARDIAC MRI

In comparison to MDCT, the advantages of cardiac MRI are

the lack of radiation exposure, avoidance of iodinated contrast

media, and better temporal resolution. Furthermore, short-axis

CHAPTER 18/ MDCT ASSESSMENT OF LEFT-VENTRICULAR FUNCTION 193

images are readily available, and time-consuming secondary reformations as required in MDCT are not needed. Therefore, the software-assisted automatic or even the interactive creation of short-axis orientated reformations during data acquisition, as provided by state-of-the art cardiac MR scanners, would lead to an improved applicability of global left-ventricular volumet- ric and functional measurements in a clinical setting.

Considering contrast media application, radiation exposure, and limited temporal resolution, the use of MDCT solely for analysis of cardiac function parameters seems not unreason- able at present time. Regarding radiation exposure, a substan- tial reduction may be achieved by the application of an ECG-triggered tube current modulation. However, the combi- nation of noninvasive coronary artery imaging and determina- tion of global left-ventricular function within one single breath-hold MDCT study, however, might be an interesting approach to a fast and conclusive cardiac workup in different cardiac diseases, e.g., patients with suspected coronary artery disease. This application of MDCT might be of clinical rel- evance for patients who are not suitable for cardiac MRI be- cause of specific contraindications.

Table 3

Volumetric and Functional Left-Ventricular Parameter As Determined by Means of MDCT and SSFP Cine MRI, N = 30

MDCT SSFP Cine MRI MDCT vs MRI

Mean± SD Range Mean± SD Range r = p <

LV-EDV [mL] 138±31 87–228 142±32 88–211 0.93 0.001

LV-ESV [mL] 53±21 20–108 54±22 27–123 0.94 0.001

LV-EF [%] 61±10 40–77 62±10 41–75 0.89 0.001

LV-SV [mL] 84±20 48–140 86±21 51–142 0.88 0.001

CI, confidence interval; LV-EDV, left-ventricular end-diastolic volume; LV-ESV, left-ventricular end- systolic volume; LV-EF, left-ventricular ejection-fraction; LV-SV, left-ventricular stroke volume; MDCT, multidetector-row computed tomography; MRI, magnetic resonance imaging; SD, standard deviation; SSFP, steady-state free precession. From ref. 15.

SUMMARY

The assessment of global functional and volumetric left- ventricular parameters has become feasible using MDCT stud- ies of the heart. Although this application is still in an experimental stage, initial studies from different study groups have revealed promising results in comparison to established techniques as CVG, echocardiography, and cardiac MRI. Recent developments in postprocessing and analysis software have improved clinical applicability.

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Table 4

Volumetric and Functional Left-Ventricular Parameter As Determined by MDCT and SSFP Cine MRI ^a

HR < 65/min HR ≥ 65/min

N = 20 N = 10

Mean ± SD Mean ± SD

HR—Mean 58.1 ± 5.5 71.2 ± 6.2 < 0.001

HR—Range 47–64 65–88 < 0.001

MDR-CT Cine MRI p MDR-CT Cine MRI p

LV-EDV (mL) 142.7 ± 32.8 143.7 ± 34.3 n.s. 129.3 ± 22.3 134.6 ± 25.8 n.s.

LV-ESV (mL) 57.3 ± 20.9 56.5 ± 23.8 n.s. 45.9 ± 17.3 48.1 ± 17.7 n.s.

LV-EF (%) 58.9 ± 10.6 61.2 ± 10.4 n.s. 65.3 ± 9.8 64.7 ± 8.9 n.s.

HR, heart rate; LV-EDV, left-ventricular end-diastolic volume; LV-ESV, left-ventricular end-systolic volume; LV-EF, left-ventricular ejection-fraction; MDCT, multidetector-row computed tomography; MRI, magnetic resonance imaging; SD, standard deviation; SSFP, steady-state free precession; n.s., not statistically significant.

a

Comparison of MDCT data sets reconstructed by biphasic adaptive cardiac volume algorithm with regard to mean HR

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