Imaging
Measuring Left Ventricular Ejection Fraction – Techniques and Potential Pitfalls
Thomas A Foley,1 Sunil V Mankad,2 Michael F Morris,1 Nandan S Anavekar,2 Todd D Miller2 Crystal R Bonnichsen,3 and Philip A Araoz1 1. Radiologist, Department of Radiology; 2. Cardiologist; 3. Cardiology Fellow, Division of Cardiology, Department of Medicine, Mayo Clinic, Rochester, US
Abstract
Prognosis and therapeutic decisions are often based on left ventricular ejection fraction (LVEF), which means the LVEF needs to be accurately measured. Many imaging modalities can measure LVEF. Each of these modalities is subject to measurement errors that can lead to the inaccurate calculation of LVEF. This article reviews the most common non-invasive imaging modalities – i.e., echocardiography, magnetic resonance imaging (MRI), computed tomography (CT), radionuclide angiography, gated myocardial perfusion single-photon emission computed tomography (SPECT) and gated myocardial perfusion positron emission tomography (PET) – used to measure LVEF, as well as the common sources of error with each of them. It is important to understand these sources of errors in order to prevent them, and recognise them when they do occur so that they can be corrected if possible.
Keywords
Left ventricular ejection fraction, echocardiography, magnetic resonance imaging, computed tomography, radionuclide angiography, multiple-gated acquisition, single-photon emission computed tomography
Disclosures: The authors have no conflicts of interest to declare. Received: 6 January 2012 Accepted: 9 March 2012 Citation: European Cardiology, 2012;8(2):108–14 Correspondence: Philip Araoz, Department of Radiology, Mayo Clinic, 200 1st Street SW, Rochester, MN 55905, US. E:
paraoz@mayo.edu
Left ventricular ejection fraction (LVEF) is one of the most commonly reported measures of left ventricular (LV) systolic function. It is the ratio of blood ejected during systole (stroke volume) to blood in the ventricle at the end of diastole (end-diastolic volume). If the LV end-diastolic volume (EDV) and end-systolic volume (ESV) are known, LVEF can be determined using the following equation:
LVEF = stroke volume (EDV - ESV) ÷ EDV
LVEF can be determined using several invasive and non-invasive imaging modalities, either subjectively by visual estimation or objectively by quantitative methods. This article focuses on the common sources of error in the quantitative calculation of the LVEF using non-invasive methods – i.e., echocardiography, magnetic resonance imaging (MRI), computed tomography (CT), gated equilibrium radionuclide angiography (commonly referred to as multiple-gated acquisition [MUGA] scan) and gated myocardial perfusion imaging with either single-photon emission computed tomography (SPECT) or positron emission tomography (PET). LVEF can also be measured non-invasively using the ‘first-pass’ radionuclide technique, but this technique is rarely performed in the current era and will not be addressed further here.
Currently, there is no universally accepted ‘gold standard’ for measuring LVEF. Every method and modality used to measure the LVEF is subject to factors that may introduce error and/or variability into the calculated ejection fraction. Because there is no gold standard, the choice of modality used should depend on patient
108
factors, local resources, other information desired from the study and the need for follow-up measurements. Knowing the methods and their pitfalls can help clinicians understand the sources of variability when measuring LVEF and choose the adequate method. For example, all techniques – except echocardiography – require obtaining information over several cardiac cycles, the image acquisition being ‘gated’ with the patient’s electrocardiogram (ECG), and calculated LVEF in patients with significantly irregular rhythms are often inaccurate if methods requiring gating are being used.
General Sources of Error
With any method, the endocardial border needs to be accurately detected to ensure accurate LV cavity detection and LVEF calculation. With methods requiring manual measurement of the LV cavity, errors can arise from differences in the perception of the endocardial border between different people or from variations in measurement technique. With automated or semi-automated methods, human variability is limited, but errors can arise from differences in the software algorithms used to detect the LV cavity border. Also important for LVEF calculation is the accurate detection of true end-diastole and end-systole. LVEF will be underestimated if either the true end-diastole (underestimated EDV) or end-systole (overestimated ESV) is not measured. With manual techniques, this depends on accurate human detection of end-diastole and end-systole. With all techniques, this also depends on sufficient temporal sampling of LV volumes to detect the largest and smallest LV ones. Techniques with lower temporal sampling may not image the true end-diastole or end-systole.
© TOUCH BRIEFINGS 2012
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76