André Capderou

Modeling, segmentation, and caliber estimation of bronchi in high resolution computerized tomography

Accurate estimation of bronchial caliber in high resolution computerized tomography (HRCT) is essential for physicians in the management and following of patients with airway disease. Although there are at present different methods of bronchi analysis, none of them can provide an absolute diagnosis of bronchial caliber. The present paper addresses a new approach of bronchi segmentation in HRCT in order to estimate the bronchial caliber. The method developed is based on mathematical morphology theory, and relies on morphological filtering, marking techniques derived from the concept of connection cost, and conditional watershed-based segmentation. In order to evaluate the robustness of the segmentation and the accuracy of the caliber estimates, a realistic bronchi modeling based on physiological characteristics has been developed. It is shown that, according to the size of the bronchi, the estimation accuracy is up to 90%.

Comparison of bedside measurement of cardiac output with the thermodilution method and the Fick method in mechanically ventilated patients

IntroductionBedside cardiac output determination is a common preoccupation in the critically ill. All available methods have drawbacks. We wished to re-examine the agreement between cardiac output determined using the thermodilution method (QTTHERM) and cardiac output determined using the metabolic (Fick) method (QTFICK) in patients with extremely severe states, all the more so in the context of changing practices in the management of patients. Indeed, the interchangeability of the methods is a clinically relevant question; for instance, in view of the debate about the risk–benefit balance of right heart catheterization.Patients and methodsEighteen mechanically ventilated passive patients with a right heart catheter in place were studied (six women, 12 men; age, 39–84 years; simplified acute physiology scoreII, 39–111). QTTHERM was obtained using a standard procedure. QTFICK was measured from oxygen consumption, carbon dioxide production, and arterial and mixed venous oxygen contents. Forty-nine steady-state pairs of measurements were performed. The data were normalized for repeated measurements, and were tested for correlation and agreement.ResultsThe QTFICK value was 5.2 ± 2.0 l/min whereas that of QTTHERM was 5.8 ± 1.9 l/min (R = 0.840, P < 0.0001; mean difference, -0.7 l/min; lower limit of agreement, -2.8 l/min; upper limit of agreement, 1.5 l/min). The agreement was excellent between the two techniques at QTTHERM values <5 l/min but became too loose for clinical interchangeability above this value. Tricuspid regurgitation did not influence the results.Discussion and conclusionsNo gold standard is established to measure cardiac output in critically ill patients. The thermodilution method has known limitations that can lead to inaccuracies. The metabolic method also has potential pitfalls in this context, particularly if there is increased oxygen consumption within the lungs. The concordance between the two methods for low cardiac output values suggests that they can both be relied upon for clinical decision making in this context. Conversely, a high cardiac output value is more difficult to rely on in absolute terms.

Multidetector row computed tomography to assess changes in airways linked to asthma control.

Background: In asthma, multidetector row computed tomography (MDCT) detects abnormalities that are related to disease severity, including increased bronchial wall thickness. However, whether these abnormalities could be related to asthma control has not been investigated yet. Objective: Our goal was to determine which changes in airways could be linked to disease control. Methods: Twelve patients with poor asthma control were included and received a salmeterol/fluticasone propionate combination daily for 12 weeks. Patients underwent clinical, functional, and MDCT examinations before and after the treatment period. MDCT examinations were performed using a low-dose protocol at a controlled lung volume (65% TLC). Bronchial lumen (LA) and wall areas (WA) were evaluated at a segmental and subsegmental level using BronCare software. Lung density was measured at the base of the lung. Baseline and end-of-treatment data were compared using the Wilcoxon signed-rank test. Results: After the 12-week treatment period, asthma control was achieved. Airflow obstruction and air trapping decreased as assessed by the changes in FEV1 (p < 0.01) and expiratory reserve volume (p < 0.01). Conversely, LA and WA did not vary significantly. However, a median decrease in LA of >10% was observed in half of the patients with a wide intra- and intersubject response heterogeneity. This was concomitant with a decrease in lung density (p < 0.02 in the anteroinferior areas). Conclusions: MDCT is insensitive for demonstrating any decrease in bronchial wall thickness. This is mainly due to changes in bronchial caliber which may be linked to modifications of the elastic properties of the bronchopulmonary system under treatment.

Non-invasive assessment of technetium-99m albumin transit time distribution in the pulmonary circulation by first-pass angiocardiography

This study describes a non-invasive method for assessment of the lung transit time distribution of a tracer, using first-pass technetium-99m albumin angiocardiography and a model-free method of deconvolution. Ten patients received a first injection of 1 MBq kg−1 in the external jugular vein to position a gamma camera in the left anterior oblique position and two additional injections (5 MBq kg−1 to record first-pass angiocardiographic data. Right and left ventricular time-activity curves were derived from regions of interest every 0.5 s over a 1-min period. The left ventricular curve was deconvoluted by the right ventricular curve to obtain the lung transport function. The deconvolution procedure was based on a modified version of the Kalman filtering technique. The procedure was repeated at an interval of 30 min in eight patients. Two patients were re-examined up to 2 years later. Skewness, kurtosis and relative dispersion of the distributions did not change over time. We also found that the distribution, once normalized by its first moment, was independent of isolated changes in heart rate or cardiac output. Comparison of curve shapes at an interval of 30 min by point by point analysis demonstrated the reproducibility of the technique. We conclude that computation of the pulmonary transit time distribution of99mTc-albumin from a standard angiocardiography procedure by model-free deconvolution is reliable and reproducible over time. We suggest that it may be a valuable toot for the non-invasive follow-up of the pulmonary circulation.

Diagnosis of Functionally Significant Coronary Stenosis with Exercise CT Myocardial Perfusion Imaging

PURPOSE To assess the feasibility of exercise perfusion computed tomography (CT) in patients suspected of having hemodynamically significant coronary stenosis. MATERIALS AND METHODS This study had institutional review board approval, and all patients gave informed consent. Thirty-two consecutive patients (26 men [mean age, 63 years] and six women [mean age, 71 years]) with 55 coronary stenoses of at least 50% underwent coronary CT angiography (one stenosis in 13 patients, two stenoses in 15 patients, and three stenoses in four patients). CT myocardial perfusion imaging was performed within 1 minute after patients performed supine exercise on an ergometer secured to the CT table. The pressure-rate product was computed to assess level of exercise. The myocardial enhancement ratio between stenotic and normally perfused territories was determined for each stenosis. Fractional flow reserve less than 0.8, as measured during invasive coronary angiography, was the reference for defining significant stenoses. Receiver operating characteristic curves were constructed to determine the myocardial enhancement ratio cutoff value. RESULTS In the per-patient analysis, a myocardial enhancement ratio cutoff of 0.8 performed best for identifying functionally significant stenosis: Sensitivity was 95% (21 of 22 patients), specificity was 90% (nine of 10 patients), positive predictive value was 95% (21 of 22 patients), negative predictive value was 90% (nine of 10 patients), and accuracy was 94% (30 of 32 patients). Corresponding values in the per-stenosis analysis were 97% (29 of 30 stenoses), 96% (23 of 24 stenoses), 97% (29 of 30 stenoses), 96% (23 of 24 stenoses), and 96% (52 of 54 stenoses), respectively. CONCLUSION Exercise CT myocardial perfusion imaging is feasible and accurate for assessment of the functional significance of coronary stenosis.

Assessment of Lung Physiology Using Pulmonary Function Tests

The lung combines two basic functions linked to respiration; first gas exchange, consisting of the oxygenation of the incoming desaturated venous blood and the removal of carbon dioxide, thus producing arterialized blood, and second, and consequently, the removal of protons (H+) from this incoming blood, permitting fast regulation of the blood concentration of H+ (pH) (Dejours 1975). To perform this task adequately, ventilation and circulation within the lung must be matched so that the ratio of the distribution of ventilation to that of perfusion is optimum. The ventilation-perfusion ratio ultimately determines the functional performance of the lung in terms of gas exchange at a given level of ventilation (Riley and Cournand 1949). Measurement of blood gases is the most relevant test available to give a global assessment of gas exchange in a given patient. Unfortunately blood gas values, when abnormal, give no clue as to what aspect of lung function is impaired. Furthermore, these values tend to become abnormal only in the late or acute phase of lung diseases, because of the remarkable flexibility of ventilationperfusion control.