Cardiac Imaging System Research Articles

The 50th anniversary of echocardiography: are we at the dawn of a new era?

Disease is very old, and nothing about it has changed. It is we who change, and we learn to recognise what was formally imperceptible. J.M. Charcot (1825–1893) Before the development of cardiovascular imaging techniques, clinicians could only imagine how the heart of their patients was contracting. It was not until the introduction of contrast ventriculography and quantitative methods for analysis in the early 1960s that objective data could be substituted for the subjective bedside observations. These developments irrevocably changed cardiology from an art to a science. Computer-aided systems were subsequently developed for more accurate analysis and reproducible measurements. In the past 20 years, advances in digital techniques and the imagination and creativity of many have resulted in an enormous progress in complex cardiac imaging modalities including ultrasound imaging, SPECT, multislice-CT, MR and PET[1]. These advances will undoubtedly accelerate as our reliance on imaging techniques for management of cardiovascular disease will continue to increase[1]. Who could have predicted 30 years ago the impressive evolution of cardiac ultrasound imaging systems? The technique paralleled the developments in microprocessor technology, it did not mimic the existing imaging modalities by providing tomographic images of the heart and it introduced new pathophysiologic and diagnostic concepts. As a consequence, it opened new horizons for clinical research and made unique contributions to our understanding of cardiac disease. With the increasing imaging performance, the number of functions and Doppler assessment of hemodynamics, all of which can be applied in a wide variety of clinical scenarios, it has become the most widely disseminated cardiac imaging technology. Currently, more than one out of every four medical imaging studies is performed worldwide with ultrasound and the proportion is still increasing. With the progress in miniaturisation and microprocessor technology cardiac ultrasound imaging continues to evolve rapidly (Fig. 1). We …

In vitro modulation of intracellular oxidative stress of endothelial cells by diagnostic cardiac ultrasound.

Diagnostic cardiac ultrasound are commonly assumed to pose no hazard to the patient-but this is not synonymous with being biologically inert. The production of intracellular reactive oxygen species (ROS) on endothelial cells is a key modulator of atheroprotective (at low level) and atherogenic (at high levels) actions. The aim of the study was to evaluate in vitro the effects on intracellular ROS of endothelial cells after ultrasound exposure of variable duration with commercially available cardiac imaging systems. Endothelial cells fluorescence was evaluated in vitro after sham (transducer off) exposure to ultrasound and after 5', 15' and 30' of ultrasound irradiation with second harmonic 1.3/2.6 MHz cardiac ultrasound scan (mechanical index 1.5). Intracellular ROS were 83 at baseline, and rose to 86, 112 and 122 fluorescence intensity at 1 h incubation after 5', 15' and 30' of ultrasound exposure respectively (P<0.01 for 30' versus baseline and 5' comparison). There were microscopic signs of endothelial damage only following 30' stage. Ultrasound exposure induced significant DNA laddering and LDH leakage after 15' of ultrasound exposure. Effects on endothelial cells could be reproduced by adding exposed extracellular medium to unexposed cells, and could be prevented removing exposed medium from cell culture or pretreating the medium with catalase. Cardiac ultrasound of current clinical diagnostic use increases intracellular oxidative stress on endothelial cells in vitro. This increase is accompanied by morphological evidence of endothelial damage only after longer exposure times, persists 1 h after withdrawal of ultrasound, and can be modulated over a wide range according to the duration of ultrasound exposure. Free radical production in the extracellular medium is the likely mediator of ultrasound effect.

Rapid evaluation of right ventricular volume and mass without breath-holding using real-time interactive cardiac magnetic resonance imaging system

Rapid evaluation of right ventricular volume and mass without breath-holding using real-time interactive cardiac magnetic resonance imaging system

Rapid evaluation of left ventricular volume and mass without breath-holding using real-time interactive cardiac magnetic resonance imaging system

Rapid evaluation of left ventricular volume and mass without breath-holding using real-time interactive cardiac magnetic resonance imaging system

Rapid evaluation of left ventricular volume and mass without breath-holding using real-time interactive cardiac magnetic resonance imaging system

OBJECTIVES The purpose of this study was to validate cardiac measurements derived from real-time cardiac magnetic resonance imaging (MRI) as compared with well-validated conventional cine MRI. BACKGROUND Although cardiac MRI provides accurate assessment of left ventricular (LV) volume and mass, most techniques have been relatively slow and required electrocardiogram (ECG) gating over many heart beats. A newly developed real-time MRI system allows continuous real-time dynamic acquisition and display without cardiac gating or breath-holding. METHODS Fourteen healthy volunteers and nine patients with heart failure underwent real-time and cine MRI in the standard short-axis orientation with a 1.5T MRI scanner. Nonbreath-holding cine MRI was performed with ECG gating and respiratory compensation. Left ventricular end-diastolic volume (LVEDV), left ventricular endsystolic volume (LVESV), ejection fraction (EF) and LV mass calculated from the images obtained by real-time MRI were compared to those obtained by cine MRI. RESULTS The total study time including localization for real-time MRI was significantly shorter than cine MRI (8.6 ± 2.3 vs. 24.7 ± 3.5 min, p < 0.001). Both imaging techniques yielded good quality images allowing cardiac measurements. The measurements of LVEDV, LVESV, EF and LV mass obtained with real-time MRI showed close correlation with those obtained with cine MRI (LVEDV: r = 0.985, p < 0.001; LVESV: r = 0.994, p < 0.001; EF: r = 0.975, p < 0.001; LV mass: r = 0.977, p < 0.001). CONCLUSIONS Real-time MRI provides accurate measurements of LV volume and mass in a time-efficient manner with respect to image acquisition.

Differences due to collimator blurring in cardiac images with use of circular and elliptic camera orbits

Background. In cardiac imaging systems, an elliptic acquisition orbit about the patient can be used to enhance resolution of single photon emission computed tomography (SPECT) images by minimizing the distance between the object imaged and the rotating detector system. In this study artifacts from images acquired with the standard circular acquisition are compared with those acquired with various elliptic acquisitions. Methods and Results. With the use of elliptic camera orbits of different eccentricities, simulated projection data were generated from a slice through the left ventricle (LV). The projection data included a simulation of the degradation due to the depth-dependent response of the collimator. As is common in many clinical systems, SPECT images were reconstructed with the standard filtered backprojection algorithm without correction for the collimator response. When the ratio of the major-to-minor axis of the acquisition arc is changed from 1 (circular) to 1.5 (elliptic), reconstructed SPECT images show an additional loss of counts (about 10%) in the apical region of the LV. The severity of the apical defect is also dependent on the starting angle of the acquisition arc. When the starting angle is changed from 0° (detector parallel to the major axis of the LV) to 60°, the ratio between the minimum count in the apical region and the maximum count in the left ventricular myocardial wall decreases by as much as 20%. Conclusions. SPECT image artifacts from elliptic acquisitions are significantly more severe than those from circular acquisitions. Because of the significant difference in images reconstructed from circular and elliptic acquisitions, standardized normal files acquired from circular acquisitions should not be used for comparisons with patient data acquired from elliptic acquisitions. (J Nucl Cardiol 2001;8:458-65.)

Tissue Doppler to Assess Diastolic Left Ventricular Function.

Doppler indices of left ventricular (LV) filling have been used traditionally for the assessment of LV diastolic function. In many circumstances, however, the interpretation of these indices is difficult because they respond to alterations of different physiological variables such as preload, relaxation, and heart rate. A typical example of their limitation is seen in patients with abnormal LV relaxation and increased preload compensation, who often present a "pseudonormal" LV filling pattern. Thus, there is a need for noninvasive indices of diastolic function capable of discriminating the effects of relaxation and preload. Tissue Doppler echocardiography (TDE) is available in most modern cardiac ultrasound imaging systems. TDE can be used to obtain regional myocardial velocities during isovolumic relaxation, early filling, and atrial systole with high spatial and temporal resolution. This article discusses the complementary role, limitations, and future challenges of TDE in the study of diastolic function.

Variability of radiation output dynamic range in modern cardiac catheterization imaging systems.

Automatic exposure control (AEC) is one of the most important characteristics for optimizing cardiac catheterization imaging; this allows the X-ray system to provide sufficient radiation output under a variety of clinical conditions so that a satisfactory image is obtained. AEC was assessed in 97 cardiac catheterization laboratories using a standard set of phantoms. Three different copper attenuators were used to simulate three patient sizes. As magnification increased, many systems had limited dynamic range and were unable to increase radiation output. With increasing atttenuator thickness, the problem worsened. With the thickest attenuator and largest magnification (4.5"-5.0" FOV), 60% of systems could not achieve the typical 70% increase in exposure while 20% were unable to increase radiation output at all.

New Real-time Interactive Cardiac Magnetic Resonance Imaging System

New Real-time Interactive Cardiac Magnetic Resonance Imaging System

New real-time interactive cardiac magnetic resonance imaging system

New real-time interactive cardiac magnetic resonance imaging system

Dynamic 3-D-echo in the preoperative assessment of left atrial myxoma in a 51-year-old male

1. Case report the large myxoma. In addition to TTE and TEE, three-dimensional echocardiography provided addiA 51-year-old male was admitted to our hospital, tional views of the valve leaflets and valvular apbecause of a decrease in physical ability and paratus (Fig. 2). The valve was found to be fully dyspnoea on strain imposed by ordinary day-to-day competent (Fig. 3). Left heart catheterization exactivities. On physical examination a diastolic murcluded a coronary heart disease and confirmed the mur was heard best over the apex. Blood laboratory hemodynamic assessment by TTE and TEE, but did results were within normal limits. Pulmonary vascunot provide any additional information with respect to lar markings were slightly enlarged as shown by the tumor or the mitral valve. Computer-tomography X-ray. ECG showed atrial fibrillation. A left intraatrior magnetic resonance imaging were not carried out. al mass could be visualized using transthoracic The tumor was removed without complications. echocardiography. The mean diastolic pressure graHistological examination revealed myxoma. dient at the mitral valve was found to be 10 mmHg. A moderate tricuspid regurge and a slightly elevated systolic pulmonary artery pressure (PAP 535 mmHg) s were found. Multiplane transesophageal echocardiog2. Discussion raphy with subsequent three-dimensional image reconstruction (Fig. 1) (ATL-APOGEE 800-Tom Tec Left atrial myxoma is the most common cardiac Imaging SystemInc., USA) was performed, using tumor, but still a rare finding [1]. Today different the software ‘Tom Tec Imaging Systems GmbHechocardiographic approaches, like TTE, TEE, DopEcho-Scan 3.0’, and confirmed the TTE results. The pler and contrast echocardiography are well estabreconstruction required 5 h. lished in the diagnosis of this disease [2–7]. Three-DAdditional information was gained by TEE showecho is a new echocardiographic imaging technique ing the attachment of the tumor to the intraatrial which we used in this case. The 3-D-echo reconstrucseptum. Sufficient Doppler signal with respect to the tion provides new views compared with the standard transmitral flow could not be recorded because the transthoracic and transesophageal echocardiography left atrium and the mitral valve anulus were filled by views. Therefore it can deliver more diagnostic information about the region of interest [8]. One of the limitations of this method is the large tube *Corresponding author. Tel.: 149 3

Automated determination of left ventricular volume curves from bi-plane digital angiography without explicit use of edge detection algorithms.

Automated computation of left ventricular (LV) global and regional function using contrast angiography has not yet become a routine procedure with the advent of digital cardiac imaging systems. We describe a new technique to compute LV volume curves which does not require the use of manual or semi-automated detection of endocardial borders and provides on-line implementation of volumetric curves and computation of pressure volume loops during catheterization. The approach uses the concepts of variable entropy (or information) of left ventricular images throughout the cardiac cycle. LV volume curves are computed with an interpolation scheme using those LV volume curves of a patient data base which are associated with the closest variation in entropy in the RAO projection to the analyzed patient data according to a simple metric. Computed LV volume curves were correlated with those obtained with manual tracing. Left ventricular ejection fraction (LVEF), time to end systole (TES) and angiographic cardiac output (CO) were compared to those obtained with the manual method. Results using a data base of 365 patients revealed excellent correlation (r = 0.97) between manually derived volume curves and volume curves computed with the automated technique within a large range of LVEFs. In 87% of all cases the computed LVEF values were found within +/- 10% of the value obtained with the gold standard method. The systolic phase of the volume curves showed that 81% of all cases had the same accuracy. The TES showed much more variation due to undersampling of the cardiac cycle in time (r = 0.71).

Coronary arteriography for quantitative analysis: Experimental and clinical comparison of cinefilm and video recordings

Although use of videotape for the recording of coronary angiograms continues to grow, the validity of quantitative coronary angiographic analysis of video images remains unknown. To estimate the realibility of angiographic images recorded on videotapes, experimental and clinical angiograms were recorded simultaneously on both 35 mm cinefilm and super-VHS videotape with normal images and with spatial filtering of the images (edge enhancement) on a digital cardiac imaging system. The experimental angiographic studies were performed with plexiglass blocks and stenosdis phantom of 0.5 to 3.0 mm in diameter. The clinical angiograms were recorded in 20 patients undergoing percutaneous transluminal coronary angioplasty (31 frames before and 20 frames after percutaneous transluminal coronary angioplasty). The cinefilm and corresponding videotapes were analyzed off-line with the new version of the coronrary angiography analysis system. For the experimental study, measurements of minimal luminal diameter obtained from cinefilm, normal-image videotape, and edge-enhanced videotape were compared with the true phanton diameter. In the clinical study the agrrement between measurements obtained from cinefilm and measurements from normal-image videotape and edge-enhanced videotape was examined. In the phantom series the accuracy and precision of quantitative coronary angiography measurement for cinefilm were −0.10 ± 0.08 mm, for normal-image videotape −0.11 ± 0.18 mm, and for edge-enhanced videotape − 0.10 ± 0.11 mm (mean ± SD). In the clinical series, the differences between measurements from cinefilm and normal-image videotape were 0.14 ± 0.20 mm and from cinefilm and edge-enhanced videotape 0.04 ± 0.13 mm. In the experimental phantom study, the use of cinefilm resulted in the most precise measurements. In the clinical study, edge-enhanced videotape provided the highest agreement with measurements obtained from cinefilm. These findings suggest that cinefilm is moore reliable than video as a recording medium for quantitative coronary analysis in scientific studies; however, for routine practice, videotape and edge-enhanced images may provide an acceptable alternative.

994-94 Use of Moderately Lossy JPEG Compression Does Not Result in Loss of Diagnostic Information in Digital Coronary Angiograms

Digital image compression is a means of reducing storage and exchange requirements for coronary angiograms. In order to assess the diagnostic accuracy of image compression, digital coronary arteriograms were analyzed in compressed and noncompressed formats. The effect on visual assessment of stenosis severity of digital coronary angiograms was evaluated on a set of 100 image sequences using lossy (15: 1) Joint Photographic Experts Group (JPEG) compression software. A panel of 3 angiographers reviewed 6200 frames from 10 clinical exams both with and without standard JPEG compression. Original and compressed versions of each sequence were viewed in random order by all panel members blinded to compression status. Images were viewed on the same display used for digital acquisition with the Philips Digital Cardiac Imaging (DCI) System. Panelists identified and graded severity of 99 stenoses in quartiles with &gt;50% considered to be significant. There was no significant difference in the number of lesions identified with each modality. Overall agreement for severity of all lesions between compressed and non-compressed modalities was 0.60 and Kappa = 0.52. If lesions were dichotomized into “significant” (&gt;50%) or “insignificant” (≤50%), agreement was 0.94 and Kappa = 0.88, suggesting that when disagreement occurred, it tended to be within one severity grade. These agreement statistics are consistent with previously reported intra-observer variability in the review of cine-coronary angiograms. The significant reduction in digital storage and exchange requirements provided by lossy JPEG does not result in a decrease in diagnostic quality of digital coronary angiograms. Variability in visual assessment from original and compressed data formats is comparable to intra-observer variability from identical data formats. Therefore, JPEG compression does not result in loss of diagnostic information and is a valid means of reducing storage and exchange requirements of coronary angiograms.

Measurement of Wiener Spectra in Digital Systems

The Wiener spectrum is an important tool used to assess the noise power of an image in the spatial frequency domain, and therefore a potentially useful index in the dose optimisation of X ray imaging systems. Many workers have reported on the measurement of Wiener spectra in the literature, however, there is little comparative work done on the relative performance of different imaging modalities using Wiener spectra. The performance of digital imaging systems using Wiener spectra is evaluated and measured spectra from different modalities compared, including ultrasound, digital subtraction angiography (DSA, vascular), a digital cardiac imaging system and nuclear medicine.

Can the same edge-detection algorithm be applied to on-line and off-line analysis systems? Validation of a new cinefilm-based geometric coronary measurement software

In the Cardiovascular Measurement System (CMS) the edge-detection algorithm, which was primarily designed for the Philips digital cardiac imaging system (DCI), is applied to cinefilms. Comparative validation of CMS and DCI was performed in vitro and in vivo with intracoronary insertion of stenosis phantoms in anesthetized pigs. The “obstruction diameter” (OD) was measured at the artificial stenoses visualized by angiography with calibration at the isocenter (ISO) and catheter calibration (CATH) and compared with the true phantom diameters. A clinical comparison of OD, reference diameter (RD), and percentage diameter stenosis (DS) was performed on 70 corresponding images from post-PTCA angiograms. In vitro, OD (CMS) yielded an accuracy of 0.18 ± 0.14 mm with 100% (correlation coefficient: r = 0.97,y = 0.06 + 0.75x, standard error of estimate [SEE] = 0.09) and 0.19 ± 0.15 mm with 50% contrast ( r= 0.94,y = 0.02 + 0.81x). OD (DCI) yielded an accuracy of 0.11 ± 0.06 mm with 100% ( r= 0.99,y = -0.03 + 0.91x, SEE = 0.05) and 0.24 ± 0.13 mm with 50% contrast ( r= 0.94,y = 0.29 + 6.69x, SEE = 0.12). In vivo, OD (CMS) yielded an accuracy of 0.18 ± 0.23 mm with ISO ( r = 0.89,y = 0.02 + 0.83x, SEE = 0.22) and 0.26 ± 0.24 mm with CATH (r = 0.89, y = 0.06 + 0.72x, SEE = 0.19). OD (DCI) yielded an accuracy of 0.08 ± 0.15 mm with ISO ( r = 0.96,y = 0.08 + 0.86x, SEE = 0.14) and 0.18 ± 0.21 mm with CATH ( r = 0.92,y = 0.09 + 0.76x, SEE = 0.17). The clinical comparison showed reasonable agreement for OD only ( r = 0.81,y = 0.26 + 0.81x, SEE = 0.29). Transformation of an edge-detection algorithm from a digital to a cinefilm-based system can lead to impairment of measurement reliability.

A transputer based three-dimensional dynamic cardiac imaging system

A single-section transverse emission scanner has been adapted to trigger off patient ECG signals, allowing for the acquisition of gated blood pool tomograms at a number of slice levels through the patient's heart. The authors describe a system for the routine generation and display of surface rendered images derived from this data using a transputer based hardware system. Surface rendering algorithms have been implemented to provide an indication of the distribution of the cardiac blood pool in three dimensions, whilst the additional use of colour and/or cine sequences provide a succinct method of representing the extra information provided by gated acquisition. The transputer provides sufficient computing power to produce rendered views at a rate of about 1 frame per second, thus putting view selection fully under operator control. The success of the system described is reflected in its routine use in a busy clinical department.

Accuracy and precision of quantitative digital coronary arteriography: observer-, short-, and medium-term variabilities.

Coronary arteriograms are increasingly acquired and stored in digital format, which allows instantaneous review of the pictorial data during the cardiac catheterization procedure. To support the angiographer in choosing the optimal sizes of the recanalization devices and studying the efficacy of the recanalization procedures, we have developed a new analytical software package (Automated Coronary Analysis = ACA) on the Philips DCI (-SX) digital cardiac imaging system. The ACA-package allows the objective and reproducible assessment of the morphologic and functional severity of coronary obstructions. Required user interaction is limited to the definition of the start and end points of the coronary segment to be analyzed. Automated contour detection is based on the use of first and second derivative functions along scanlines perpendicular to the automatically computed vessel pathline in the first iteration and perpendicular to the initial contours in the second iteration. These derivative functions have been modified based on the line spread function of the X-ray imaging chain, which is of particular importance for the accurate measurement of small vessel sizes. Phantom studies have indeed demonstrated that vessel sizes down to 0.66 mm can be measured accurately and reproducibly. Inter- and intraobserver variability studies have demonstrated a variability in the obstruction diameter of 0.11 mm and 0.10 mm, respectively, and in the percent diameter stenosis of 5.64% and 3.18%, respectively. These variability studies have been extended to short-term studies with repeated acquisition in the same angiographic views after 5 min and to medium-term studies with repeated acquisition in the initial angiographic views at the end of the catheterization procedures. With these standardized repeated acquisition and analysis procedures, the variabilities in the obstruction diameters increased to 0.19 and 0.18 mm, respectively, and remained below 6% in the percent diameter stenosis (5.61% and 5.28%, respectively). With an analysis time of approximately 15 sec on the DCI-SX, an efficient tool is now available in the catheterization laboratory for the objective and reproducible assessment of vessel dimensions and changes therein as a result of recanalization procedures.

In-vivo validation of on-line and off-line geometric coronary measurements using insertion of stenosis phantoms in porcine coronary arteries.

Geometric coronary artery measurements with the Phillips Digital Cardiac Imaging System (DCI) and the Cardiovascular Angiography Analysis System (CAAS) were validated using percutaneous insertion of radiolucent stenosis phantoms in swine coronary arteries. Angiographic visualization of the stenosis lumens (phi 0.5, 0.7, 1.0, 1.4, 1.9 mm) was simultaneously recorded on DCI and cinefilm. The acquisition systems were calibrated by either the diameter of the guiding catheter (catheter CAL) or the isocenter method (isocenter CAL). Minimal luminal diameters (MLD) obtained with CAAS and DCI on 20 corresponding cineframes were compared with the true phantom diameters (PD). The accuracy of MLD measurements with the CAAS using isocenter CAL was -0.07mm, the precision 0.21 mm (r = 0.91; y = 0.30 + 0.79x; SEE = 0.19), with catheter CAL the accuracy was 0.09 mm, the precision 0.23 mm (r = 0.89; y = 0.19 + 0.74x; SEE = 0.19). The accuracy of MLD measurements using the DCI with isocenter CAL was 0.08 mm, the precision 0.15 min (r = 0.96; y = 0.08 + 0.86x; SEE = 0.14), with catheter CAL the accuracy was 0.18 mm, the precision 0.21 mm (r = 0.92; y = 0.09 + 0.76x; SEE = 0.17). DCI underestimated PD with isocenter CAL (p less than 0.05) and with catheter CAL (p less than 0.001). MLD can be measured with high accuracy, both applying on-line digital as well as off-line cineangiographic analysis. The results of digital measurements demonstrate high reliability of the new digital software package.

Evaluation of statistical methods of image reconstruction through ROC analysis (emission tomography)

Several statistical methods of image reconstruction are described and objectively compared through the use of receiver-operating-characteristic (ROC) analysis based on a specified detection task performed by a human observer. The simulated imaging system is a multiple-pinhole coded-aperture system for dynamic cardiac imaging, and the objects represent cross sections of the left ventricle at end systole. The task is detection of a profusion representing an akinetic wall segment. Thirteen different reconstruction algorithms are considered. Human observers perform the specified task on this set of reconstructions, and the results are analyzed through the use of ROC analysis. The results show that the methods that utilize the largest amount of (accurate) prior information tend to perform the best.