The role of still-frame parametric imaging in magnetic resonance assessment of left ventricular wall motion by non-cardiologists.

BACKGROUND: Cardiac magnetic resonance (MR) images are often reviewed by non-cardiologists who are not trained in the interpretation of regional left ventricular (LV) function. We hypothesized that the use of still-frame parametric MR images of wall motion could aid in the assessment of regional LV function. METHODS: Dynamic, electrocardiogram-gated, steady-state free precession (FIESTA) short-axis images were obtained in 6 to 10 slices in 18 consecutive patients. Each loop was used to automatically generate a still-frame image, in which each pixel is assigned a value equal to the amplitude of cyclic variation in local intensity, resulting in higher intensity in pixels that change between blood and tissue during the cardiac cycle. The dynamic images were reviewed by an expert cardiologist who provided gold standard grades for regional wall motion and by four radiologists. Then the radiologists reviewed and graded the same MR images in combination with parametric images. Grades assigned to each segment in the two sessions were compared with the gold standard. RESULTS: According to expert interpretation, 6 patients had normal wall motion, and 12 had wall motion abnormalities. Parametric images showed a bright band in the area spanned by endocardial motion, with reduced brightness and thickness in areas of hypokinesis. The agreement between the radiologists' grades and the gold standard significantly improved by adding parametric images (from 77% to 81%), which also resulted in reduced interobserver variability (from 52% to 33%). CONCLUSIONS: Still-frame parametric images aid in the assessment of regional wall motion by non-cardiologists who are required to interpret cardiac images.     

Effects of aging on left atrial reservoir, conduit, and booster pump function: a multi-institution acoustic quantification study

OBJECTIVE—To assess the feasibility of measuring left atrial (LA) function with acoustic quantification (AQ) and then assess the effects of age and sex on LA reservoir, conduit, and booster pump function.
PATIENTS AND SETTING—165 subjects without cardiovascular disease, 3-79 years old, were enrolled by six tertiary hospital centres.
INTERVENTIONS—Continuous LA AQ area data were acquired and signal averaged to form composite waveforms which were analysed off-line.
MAIN OUTCOME MEASURES—Parameters of LA performance according to age and sex.
RESULTS—Signal averaged LA waveforms were sufficiently stable and detailed to allow automated analysis in all cases. An age related increase in LA area was noted. LA reservoir function did not vary with age or sex. All parameters of LA passive and active emptying revealed a significant age dependency. Overall, the passive emptying phase accounted for 66% of total LA emptying ranging from 76% in the youngest to 44% in the oldest decade. LA contraction accounted for 34% of atrial emptying in all subjects combined with the older subjects being more dependent on atrial booster pump function. When adjusted for atrial size, there were no sex related differences in LA function.
CONCLUSIONS—LA reservoir, conduit, and booster pump function can be assessed with automated analysis of signal averaged LA area waveforms. As LA performance varies with age, establishment of normal values should enhance the evaluation of pathologic states in which LA function is important.


Keywords: aging; atrium; echocardiography     

Electronic transmission of digital echocardiographic studies: effects of MPEG compression

The acquisition, storage and retrieval of digital echocardiographic studies greatly facilitates image review and quantitation and permits the transmission of studies electronically. However, the considerable size of digital echocardiographic data files makes transmission over existing networks slow and impractical. Reduction in the size of these data files can be accomplished with digital image compression. We sought to evaluate the effects of MPEG-1 compression on the transfer time of digital echocardiographic studies over currently available network connections. Ninety consecutive routine clinical echocardiographic studies were randomly compressed at one of three compression ratios 60:1, 80:1, or 120:1 and sent to a receiving terminal using simulated transmission rates. Compression of digital echocardiographic studies at these ratios which, have been shown to maintain diagnostic image quality, reduced the size of digital echocardiographic studies to less than 1% of their original sizes which allowed transmission of echocardiographic studies over networks using 3ISDN or T1 lines with minimal waiting time.     

Quantitative diagnosis of stress-induced myocardial ischemia using analysis of contrast echocardiographic parametric perfusion images.

AIMS: Parametric imaging of myocardial perfusion provides useful visual information for the diagnosis of coronary artery disease (CAD). We developed a technique for automated detection of perfusion defects based on quantitative analysis of parametric perfusion images and validated it against coronary angiography. METHODS AND RESULTS: Contrast-enhanced, apical 2-, 3- and 4-chamber images were obtained at rest and with dipyridamole in 34 patients with suspected CAD. Images were analyzed to generate parametric perfusion images of the standard contrast-replenishment model parameters A, beta and A.beta. Each parametric image was divided into six segments, and mean parameter value (MPV) was calculated for each segment. Segmental MPV ratio between stress and rest was defined as a flow reserve index (FRI). Receiver operating characteristics (ROC) analysis was used in a Study group (N=17) to optimize FRI threshold and the minimal number of abnormal segments per vascular territory (LAD and non-LAD), required for automated detection of stress-induced perfusion defects. The optimized detection algorithm was then tested prospectively in the remaining 17 patients (Test group). LAD and non-LAD stenosis >70% was found in 19 and 17 patients, respectively. In the Study group, FRI threshold was: LAD=0.95 and non-LAD=0.68, minimal number of abnormal segments was four and two, correspondingly. Sensitivity, specificity and accuracy in the Test group were: 75%, 67% and 71% in the LAD, and 75%, 75% and 75% in the non-LAD territories. CONCLUSION: Automated quantitative analysis of contrast echocardiographic parametric perfusion images is feasible and may aid in the objective detection of CAD.     

Current state of intraoperative echocardiography

Intraoperative use of echocardiography is becoming more prevalent and is now considered an essential part of modern cardiac surgery. Echocardiography can be performed intraoperatively using transesophageal, epicardial or epiaortic, and substernal approaches. These techniques have a variety of applications in evaluating myocardial and valvular function, assessing aortic atheroma, and determining adequacy of various kinds of repair and reconstruction. Future applications will most likely involve more compact equipment, the implementation of epicardial and transesophageal real-time three-dimensional echocardiography, and better use of provocative methods of intraoperative testing.     

Evaluation of Left Ventricular Diastolic Performance Using Automated Border Detection

Acoustic quantification (AQ) is a noninvasive technique which provides online left ventricular (LV) area/volume waveforms. The filling portion of the AQ waveform can be used to assess LV diastolic properties. Analysis of signal-averaged AQ curves enhances the waveforms and allows reliable, quantitative, and automated analysis. From signal-averaged AQ LV waveforms, the phases of diastole can be easily detected and several parameters of diastolic performance calculated. Analysis of signal-averaged LV waveforms is complementary to that of LV AQ analysis. AQ has been used to identify diastolic dysfunction in patients with LV hypertrophy and systemic hypertension. Normal values of these parameters are age dependent and reference values will soon be available.     

Effects of coronary occlusion on high-frequency content of the epicardial electrogram and body surface electrocardiogram

The very high-frequency content (150 to 250 Hz) of epicardial electrogram waveforms was studied in 19 anesthetized dogs subjected to occlusion of left anterior descending coronary artery. Computer techniques of digital averaging and digital band-pass filtering were applied. Signals were obtained from epicardial electrodes placed in the ischemic left ventricular region and on the noninjured right ventricular surface, and from the body surface electrocardiogram. All recordings were made simultaneously before, during, and after coronary occlusion and subjected to the same analysis. The waveforms obtained from the ischemic left ventricular region showed a considerable decrease in high-frequency content, while those obtained from the noninjured right ventricular surface remained unchanged. The results correlated with the appearance of a zone of reduced amplitude in the body surface high-frequency QRS complex. Therefore, this macroscopic phenomenon measured noninvasively from the body surface is explained by local reduction of high-frequency activity in the ischemic region of the myocardium.