Ultrafast computed tomography for detection of coronary artery calcification.

This review summarizes coronary artery calcification as a marker of coronary atherosclerosis as historically noted and detected with radiographic imaging modalities. This review concentrates on the use of ultrafast computed tomography (CT) for coronary artery calcification imaging. Ultrafast CT is uniquely qualified for imaging of the coronary arteries and calcific deposits in particular because of the x-ray attenuation characteristics of calcium. Current validation studies are summarized. In particular, the sensitivity of ultrafast CT coronary calcification in angiographically proven obstructive disease has been shown by many investigators to be above 90%, but with specificity on the order of 40% to 50%. These numbers may be different for younger men and women, where the detection of smaller calcific deposits is more difficult. The positive predictive value has been calculated as between 72% by angiographic validation and 40% in a population with a lower pretest bias.

Understanding right and left ventricular systolic function and interactions at rest and with exercise in primary pulmonary hypertension.

The effort limitation in primary pulmonary hypertension (PPH) is thought to result from an inability to increase cardiac output with exercise. The precise mechanism, however, is unknown. We studied right ventricular (RV) and left ventricular (LV) function and interactions in 16 patients with PPH with electron beam computed tomography (EBCT) at rest and during supine bicycle exercise. RV and LV volumes and masses were measured at systole and diastole, and ejection fraction and cardiac index computed. Resting RV end-diastolic volume (215 +/- 72 ml) and mass (110 +/- 45 g) were increased, whereas stroke volume (65 +/- 26 ml) and ejection fraction (31 +/- 8%) were decreased. LV end-diastolic volume (80 +/- 31 ml) was decreased, whereas ejection fraction remained normal (66 +/- 9%). Cardiac index was at the lower limit of normal (2.26 +/- 0.72 L/min/m2). During exercise, RV end-diastolic volume was unchanged (196 +/- 63 ml, p = NS) but stroke volume (52 +/- 29 ml, p < 0.05) and ejection fraction (26 +/- 10%, p = 0.08) decreased. LV end-diastolic (52 +/- 22 ml, p < 0.001), end-systolic (17 +/- 8 ml, p < 0.001), and stroke volumes (35 +/- 20 ml, p < 0.001) decreased, whereas ejection fraction (65 +/- 15%, p = NS) and cardiac index remained unchanged (2.17 +/- 0.93 L/min/m2, p = NS). the ratio of RV/LV stroke volume at rest (1.21 +/- 1.06) increased with exercise (1.74 +/- 1.13, p = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of right ventricular volume in human explanted hearts using ultrafast cine computed tomography.

The quantitative measurement of right ventricular (RV) volume has been attempted by a number of methods, including nuclear magnetic resonance imaging, contrast angiography, echocardiography, and radionuclide angiography. All of these methods have limitations. Ultrafast cine computed tomographic (CT) scan is a new technology that may have an important role in on-line ventricular volume measurements. Twelve human explanted hearts, fixed in formalin, were subjected to ultrafast cine CT scans to estimate RV volume. The volumes derived from the CT scans were compared with actual fluid volumes needed to fill the RV volume measurements. All measurements were conducted independently by two observers. Actual RV volumes in the 12 hearts ranged from 29.8 ml to 174.6 ml. A strongly significant correlation between actual volume and CT volume was seen (r = 0.99). Agreement between observers was also seen to be highly significant (r = 0.992). Limitations to accurate in vivo assessment due to bolus injection of contrast medium might include alterations in ventricular pressure change. Similarly, differentiation of the endocardial border with contrast may not be as sharp as that with an air-tissue interface. This study demonstrates that RV volumes can be reliably determined by ultrafast cine CT scans in explanted hearts. On-line systolic and diastolic volumes and thus stroke volume, ejection fraction, etc, can be accurately defined independent of cardiac orientation. This technique offers opportunities to study ventricular function under various conditions.

Transfer-function analysis of UFCT myocardial time-density curves by time-varying recursive least squares analysis.

Techniques which assume linear, time-invariant systems have been used to characterize indicator dilution pairs. As a basis for fully describing the relation between left ventricular (LV) and myocardial (MYC) time-density curves, produced by an intravenous contrast medium as measured by ultrafast CT, the assumption of time invariance was tested using recursive least squares regression and CUSUM, a test for time variability of regression parameters. Using data from anesthetized dogs with concomitant microsphere information, constant and time-varying regression models, MYC(t) = b(t)LV(t-1), were generated from time-density curves of flows from two groups: Group 1 (MBF < 2 ml/min/gm, n = 11) and Group 2 (MBF > 2 ml/min/gm, n = 10). The time-varying regression models had reduced root mean square error: 0.6 +/- 1.1 and 0.5 +/- 0.8 versus 7.3 +/- 3.5 and 4.1 +/- 1.6 for Groups 1 and 2, respectively. Significant time variability (p < 0.05) by CUSUM was found in 9/11 Group 1 models and 7/10 Group 2 models. Myocardial blood volume was estimated as the average value of b(t) over the rising portion of the LV curve. Myocardial blood flow was then calculated as myocardial blood volume divided by coronary transit time, determined from gamma variate fits of the LV and scaled, shifted LV curve, with excellent results over a wide range of flows (r = 0.93, y = 0.92 x + 0.28, range of 0.4 to 6.7 ml/min/gm). These results show that measurements of increased myocardial blood flow are possible with an intravenous contrast media, and that movement of contrast medium from intravascular space to extravascular space occurs during the course of the contrast medium's first pass.

Accuracy and reproducibility of precordial percussion and palpation for detecting increased left ventricular end-diastolic volume and mass. A comparison of physical findings and ultrafast computed tomography of the heart.

OBJECTIVE: To assess the accuracy and reproducibility of indirect definitive precordial percussion in detecting increased left ventricular end-diastolic volume (LVEDV), left ventricular mass (LVM), and left ventricular end-diastolic wall thickness (LVEDWT), and to compare it with palpation of the apical impulse. DESIGN: Descriptive study. SETTING: Hospitals and clinics of a university medical center. PATIENTS: Convenience sample of 103 patients (62 men and 41 women) referred for ultrafast computed tomography (CT) of the heart. INTERVENTIONS: Percussion dullness distance from the midsternal line in the left fourth through sixth intercostal spaces, distance of the apical impulse from the midsternal line, and apical impulse diameter in the left lateral decubitus position were measured on all patients. Measurements of LVEDV, LVM, and LVEDWT were taken using ultrafast CT of the heart. Investigators performing the physical diagnostic maneuvers were blinded to the clinical history and CT results, and investigators performing the CT scans were blinded to physical findings. RESULTS: Percussion dullness distance in the left fifth intercostal space was the best discriminator of LVEDV (receiver operating characteristic [ROC] area, 0.680; 95% confidence interval [CI], 0.547 to 0.813), and dullness distance in the left sixth intercostal space was the best discriminator of LVM and LVEDWT (ROC areas, 0.831, 95% CI, 0.674 to 0.988; and 0.849, 95% CI, 0.651 to 0.999, respectively). A percussion dullness distance of greater than 10.5 cm in the left fifth intercostal space detected increased LVEDV or LVM with a sensitivity of 91.3% (95% CI, 70.5% to 98.5%) and a specificity of 30.3% (95% CI, 19.9% to 43.0%). There was moderate concordance between investigators for percussion dullness distance (kappa, 0.57; 95% CI, 0.18 to 0.96). In patients in whom an impulse was palpated, an apical impulse diameter of greater than 3.0 cm in the left lateral decubitus detected increased LVEDV or LVM with a sensitivity of 100% (95% CI, 77.1% to 100%) and a specificity of 40% (95% CI, 23.2% to 59.3%). However, an impulse was palpable in only 53% of cases and showed only slight interobserver reproducibility (kappa, 0.18; 95% CI, 0.0 to 0.58). CONCLUSION: Indirect definitive percussion of the precordium is a sensitive and moderately reproducible maneuver for excluding cardiomegaly due to increased LVEDV or LVM. Although measurement of apical impulse diameter was also sensitive in excluding cardiomegaly, lack of a palpable impulse in many patients and low precision between physicians may limit its utility in clinical practice.

Analysis of regional pulmonary enhancement in dogs by ultrafast computed tomography.

Measurement of regional pulmonary enhancement was made in five anesthetized dogs with intravenous contrast material-enhanced ultrafast computed tomography (CT). Three or four electrocardiogram-gated flow scans were performed in each dog in the prone and supine positions. Immediately after each flow scan was acquired at four levels (8-mm thick slices), 20 times per level, 0.5 mL/kg (10 mL/second) ionic contrast medium was injected into the inferior vena cavae. Each level of each lung was divided into anterior, middle, and posterior regions for time density curve analysis and regional flow estimation. Images were transferred to an off-line workstation for lung pixel colorization and subjective interpretation. There was a statistically significant gravity-related enhancement gradient in both the supine and prone positions; however, the gradient was much greater in the supine position. This study shows that gravity-related contrast medium enhancement gradients in the lung can be demonstrated by ultrafast CT.

Myocardial color perfusion images from ultrafast computed tomography.

This article presents a new method for visualization of myocardial perfusion information from ultrafast computed tomography (UFCT). Changes in myocardial density produced by intravenous contrast medium enhancement were color coded selectively and displayed in a cold to hot spectrum. Color coded images from anesthetized canines with temporarily occluded left anterior descending coronary arteries clearly showed ischemic myocardium. Other regional flow differences such as arrival times and regional heterogeneity of enhancement also were observed. An objective comparison of UFCT and microsphere data was made by the amount of ischemia and by the flow histograms of each method for control and occlusion states. The amount of ischemia detected by UFCT (5.6 +/- 2.3%) was less than that detected by microspheres (7.9 +/- 5.0%). Analysis of variance showed significant differences (P less than 0.05) caused by occluder status but not measurement method. The microsphere occlusion flow histogram was significantly different than the microsphere control and UFCT occlusion histograms at low flows. This preliminary evaluation shows promise for optimising visualization of flow patterns within the myocardium.

Validation of ultrafast computed tomographic left ventricular volume measurement.

Left ventricular volume has been measured with ultrafast computed tomography. However, the accuracy with which this can be done is unknown. We therefore imaged with ultrafast computed tomography 11 rectangular phantoms, 20 to 225 ml, and 17 left ventricular casts, 15 to 112 ml. Two observers planimetered serial tomographic images and computed volume from sequential tomograms. There was no significant inter- or intraobserver difference in measurement of phantoms. Deviation of ultrafast computed tomographic volume from true phantom volume was -0.1 +/- 3.5% SD, range 9.0 to -7.6%. Correlation of true phantom volume with ultrafast computed tomographic volume was 0.99, SEE = 1.9 ml. No significant difference was observed between merged and single ultrafast computed tomographic scanning sequences. Left ventricular cast volume determined by ultrafast computed tomography deviated from true volume by 6% +/- 20%, range 54% to -45%. Correlation of true volume with ultrafast computed tomographic volume was 0.99, SEE = 5.1 ml. There was no interobserver significant difference in measurement of left ventricular cast volume. Correlation between ultrafast computed tomographic volume and cineradiographic volume of the same left ventricular casts was 0.99, SEE = 4.4 ml. Thus, phantom volumes can be measured accurately without significant intra- or interobserver variation. Merged scanning sequences did not influence volume determination. Left ventricular cast volume determination was comparable to that obtained with cineradiography.

Measurement of myocardial blood flow by UFCT: towards clinical applicability.

This review is designed to be a summary of the research conducted towards establishing ultrafast CT as a clinically appropriate tool for measuring myocardial blood flow. The methods and techniques used in the animal validation studies are presented. The results will be critically analyzed and the conclusions discussed. The proposed improvements to flow calculation algorithms will also be addressed. Technical improvements and experimental research needed will also be addressed.

Measurement of myocardial blood flow by ultrafast computed tomography.

Myocardial blood flow was analyzed by radioisotope-labeled microspheres and ultrafast computed tomography (CT) in 16 closed-chest, anesthetized dogs. The first set of 10 dogs had CT and microsphere measurements before and after chromonar-induced increases in myocardial blood flow. A second set of six dogs had flows measured at control and during temporary reductions in regional flow produced by balloon cuff occlusion of the left anterior descending coronary artery. All dogs had four-slice, 20-instance CT scans after injection of a medium bolus (0.35 ml/kg) of contrast medium into a femoral vein simultaneous with injection of microspheres into the left atrium. CT myocardial flow was calculated as the change in myocardial CT numbers divided by the area from a blood pool time-density curve. A wide range of myocardial blood flows was produced as determined by microspheres (0 to 6.7 ml/min/g). Global flow of the first set of dogs was shown to have excellent correlation (r = .95, n = 17) for a limited range (.4 less than X less than 1.4 ml/min/g) of flows. Regional flows of these measurements demonstrated less correlation (r = .63, n = 110) but extended the range of flow to 1.7 ml/min/g. At higher flows (greater than 2.5 ml/min/g) the correlation for global and regional flows was not significantly different than zero. Regional ischemic flow correlation extended the linear range of flow to 0 ml/min/g (r = .62, n = 17). These results show that CT can measure myocardial blood flow over a limited but clinically relevant range of flows defined as slightly above normal to ischemic. These results indicate that another preparation of CT flow measurement must be sought for quantification of myocardial perfusion values significantly above normal.

Determination of cardiac output by ultrafast computed tomography.

Three methods of determining cardiac output were compared in six anesthetized dogs (23-28 kg) for the purpose of evaluating the ability of ultrafast computed tomography to measure cardiac output at three points of the circulation: pulmonary artery, left ventricle, and descending aorta. Computed tomography cardiac output is calculated by indicator dilution analysis of an iodinated contrast bolus time-density curve. Computed tomography cardiac output was compared to thermodilution and radioactive microsphere cardiac output methods. The results show very good agreement between thermodilution and computed tomography methods (r = .90) and good agreement between microsphere and computed tomography (r = .88). Comparison of computed tomography cardiac output measurements from the left ventricle and pulmonary artery was excellent (r = .99), as were measurements from the left ventricle and descending aorta (r = .97). This study also showed minimal interlevel scan-density response variability (3%) and minimal variability between experiments (7%). Therefore, it is concluded that cardiac output can be accurately measured at many points in the blood pool by ultrafast computed tomography.