Myocardial contusion [MC] is a common injury following blunt chest trauma without any specific symptoms [1Paoi M. Diagnosis of myocardial contusion after blunt chest trauma using 18F-FDG positron emission tomography Br J Radiol 2006; 79: 264-5., 2Edouard A. Contusion myocardique Conferences d'actualisation 2003; 567-74.]. It occurs in 5 - 15 % of polytraumatized population, according to the studies published in the literature [3Foot CL. Myocardial contusion Crit Care Resusc 2005; 7: 29-3.].

There is a substantial confusion concerning the diagnosis, and the definition of myocardial contusion which is not entirely clear [1Paoi M. Diagnosis of myocardial contusion after blunt chest trauma using 18F-FDG positron emission tomography Br J Radiol 2006; 79: 264-5.].

MC can induce severe complications [arrhythmias, hypotension, shock], of which most frequent is represented by the disorders of the cardiac rhythm [2Edouard A. Contusion myocardique Conferences d'actualisation 2003; 567-74.].

Myocardial contusion is characterized on microscopical examination, by focal hemorrhages with hematoma formation, as well as myofibrillar fragmentation in the wall of the heart [10Pandian NG, Skorton DJ, Doty DB, Kerber RE. Immediate diagnosis of acute myocardial contusion by two-dimensional echocardiography: study in a canine model of blunt chest trauma J Am Coll Cardiol 1983; 2: 488-96., 11Skorton DJ, Collins SM, Nichols J, Pandian NG, Bean JA, Kerber RE. Quantitative texture analysis in two dimensionel echography: Application to the diagnosis of experimental myocardial contusion Circulation 1983; 68: 217-3., 12Liedtke AJ, De Muth WE. Non penetrating cardiac injuries: a collective review Am Heart J 1973; 86: 687-97.]. The interface between the area of normal and contused tissue due to the variation of the echo reflective which increase the brightness of the ultrasound reflection [10Pandian NG, Skorton DJ, Doty DB, Kerber RE. Immediate diagnosis of acute myocardial contusion by two-dimensional echocardiography: study in a canine model of blunt chest trauma J Am Coll Cardiol 1983; 2: 488-96.]. Myocardium wall is defined as [8Shah PM, Crawford M, DeMaria A, et al. Recommendation for quantification of the left ventricle by two-dimensional echocardiography J Am Soc Echocardiogr 1989; 2: 358-67.], as follows: normal = 0; hypokinetic, [reduction of endocardial motion and thickenning] = 2; akinetic, [virtual absence of inward motion and thickening] = 3; dyskinetic, [paradoxic wall motion away from the center of the left ventricle in systole] = 4. Myocardial contusion was defined as a grade 2 or more segmental wall motion abnormality [9Brooks SW, Youg JC, Cmolik B, et al. The use of transesophageal echocardiography in the evaluation of chest trauma J Trauma 1992; 32: 761-8.].

Human observation reported that, the distinctive echocardiographic feature of myocardial contusion related to an increased brightness of the ultrasonic reflections from the contused area [10Pandian NG, Skorton DJ, Doty DB, Kerber RE. Immediate diagnosis of acute myocardial contusion by two-dimensional echocardiography: study in a canine model of blunt chest trauma J Am Coll Cardiol 1983; 2: 488-96.].

Several techniques are used to characterize MC [1Paoi M. Diagnosis of myocardial contusion after blunt chest trauma using 18F-FDG positron emission tomography Br J Radiol 2006; 79: 264-5.], such as electrocardiogram, the estimation of myocardial band fraction of creatine phosphokinase, the chest radi+ography and the scintiscanning. Unfortunately, these techniques missed the efficiency to characterize the MC [3Foot CL. Myocardial contusion Crit Care Resusc 2005; 7: 29-3., 4Elie MC. Blunt cardiac injury Mt Sinai J Med 2006; 73: 542-2., 6Boeken U, Feindt P, Gramsch-Zabel H, et al. The incidence of myocardial contusion in 160 patients with blunt chest trauma diagnostic criteria and outcome J Trauma 2000; 26: 111-5., 7Saunders CR, Doty DB. Myocadial contusion Surgery, gynecology and obstetrics 1977; 144: 595-603.] through another acquisition technique, based on the transoesophagien echocardiography [TEE] [5Goarin JP. Échographie transoesophagienne dans les traumatismes fermés du thorax, Conférences d'actualisation SFAR 1996.], anatomical structures, cardiac and vascular and hemodynamic functions on the polytraumatized patients with high quality of images, can be obtained.

Several studies have proved that TEE can provide high-quality images [13El-hawary A, Hesham H, Magdy I, Miguel Z, Fathi M. Simultaneous dobutamine transthoracic and trans-esophageal echordiography in assesing coronary arthery disease Egypt Heart J 1997; 83-93.], great sensitivity to diagnose the myocardial disease compared to echography transthoracic. The TEE may visualize segmental wall motion abnormalities which are interpretated as contusion, in patients without previous myocardial infarction or coronary artery disease [9Brooks SW, Youg JC, Cmolik B, et al. The use of transesophageal echocardiography in the evaluation of chest trauma J Trauma 1992; 32: 761-8., 14Frazee RC, Farnel MB, Miller FA. Objective evaluation of blunt cardiac trauma J Trauma 1986; 26: 510-20.].

The 2D-echocardiography image is essential to evaluate the pathologies of the cardiac muscle and specially the MC. In case of blunt chest polytraumatized patients, MC is identified qualitatively [1Paoi M. Diagnosis of myocardial contusion after blunt chest trauma using 18F-FDG positron emission tomography Br J Radiol 2006; 79: 264-5., 2Edouard A. Contusion myocardique Conferences d'actualisation 2003; 567-74.] and quantitatively [3Foot CL. Myocardial contusion Crit Care Resusc 2005; 7: 29-3.] respectively on the echographic image by:

1. An increase thickness of the myocardium at the end of the diastole.
2. An increase in the reflectivity of the echoes coming from the area contuse.
3. The measurement of the systolic ventricular function which changes when the myocardium is contused [9Brooks SW, Youg JC, Cmolik B, et al. The use of transesophageal echocardiography in the evaluation of chest trauma J Trauma 1992; 32: 761-8.].

is developed since many years in cardiology. It is a different tool which allow the assessment of certain physical feature of biological tissue based on tissue acoustic properties. Most studies, concern the estimation of the backscatter coefficient [24Wickline SA, Thomas LJ, Miller JG, Sobel BE, Perez JE. Sensitive detection of the effects of reperfusion on myocardium by ultrasonic tissue characterization with integrated backscatter Circulation 1986; 74: 389-400., 25Karpati A, Corday S, Jaffe M, Velasquez G, Aveeda J. Clinical application of ultrasonic backscatter in transesophageal echocardiography to detect ischemic myocardium J Am Coll Cardiol 1987; 13: 226A.]. In the case of a healthy heart, this parameter follows the variation of those of the cardiac cycle [24Wickline SA, Thomas LJ, Miller JG, Sobel BE, Perez JE. Sensitive detection of the effects of reperfusion on myocardium by ultrasonic tissue characterization with integrated backscatter Circulation 1986; 74: 389-400.]. In the case of an acute ischemia, the amplitude of the cyclic variation decreases [25Karpati A, Corday S, Jaffe M, Velasquez G, Aveeda J. Clinical application of ultrasonic backscatter in transesophageal echocardiography to detect ischemic myocardium J Am Coll Cardiol 1987; 13: 226A.]. The cyclic variations of the backscatter coefficient change with an hypertrophic cardiomyopathy or an acute rejection.

The texture analysis is an another approach of clinical echocardiographic image analysis. The echocardiographic image texture is related to the random interferences on the transducer surface between the waves scattered by the scatterers (small structures). Our interest is based on myocardial texture analysis of 2D echocardiography could identify the alterations attributed to abnormal tissue. The texture measurements are based on statistical descriptions of the spatial distribution of gray levels.

In the literature, quantitative texture analysis has been reported to allow identification of contused myocardium by analysis of gray level distribution in a caninemodel of myocardial contusion [25Karpati A, Corday S, Jaffe M, Velasquez G, Aveeda J. Clinical application of ultrasonic backscatter in transesophageal echocardiography to detect ischemic myocardium J Am Coll Cardiol 1987; 13: 226A.].

It has been observed that several parameters derived from the texture analysis [TA.] are discriminating. In addition, the contused area is strongly echoic. The observation shows the difference in the gray levels between the contused and normal areas i.e. the gray level of the former is higher than the latter. It is important to note that no investigations made so far on the subject.

Among these methods used in such approaches, there are also statistical approaches based on:

1. The first order statistics which exploits notably the histogram of gray level by measure of gray level average, the variance or the moments of superior degree [21Pratt WK. Digital image processing. New York: John Willey 1991.]. The Max-Min, developed initially by Mitchell [22Mitchell OR, Myers CR, Boyne W. A max-min measure for image texture analysis IEEE Transact Comput 1977; 408-14.], is an algorithm which measures the local extrema of signal and of which the textural parameters (slope and intercept) can be used to discriminate the different textures.
2. The second order statistics is based on density of probabilities of a group of pixels (minimum two pixels) and takes into consideration the relation of spatial dependence between the pixels.

Haralick [23Haralick RM. Stastical and structural approaches to texture Proc IEEE 1979; 67: 786-804.] describes eight statistical approaches which permit the measuring and characterization of texture. The robust methods more often used are the co-occurrence matrices and run length matrices.

The purpose of our study concerns the altered acoustic properties of acute myocardal contusion. This could be determined by a quantitative analysis based on texture analysis and statistical classification (Leave-one-out and multivariate method) of two-dimensional transesophageal echocardiography.

The study deals only with patients who had suffered from blunt chest trauma and benefited through transesophageal echocardiography exam.

Patients suffering from a previous coronary artery disease or having a chronic or acute pathology of the esophagus (contraindicating for transesophageal echocardiography exam) were excluded segmental wall motion abnormality was semi-quantitatively graded by two echocardiographic images of 19 patients (Table 1) with segmental wall motion abnormalities, considered to be related to myocardial contusion were further analyzed. The echography exam for all patients was taken at Henri Mendor hospital, reanimation department.

Table 1

Demographic SAPS

From each image, a region of interest at end-diastole and end-systole is taken, and 2D spatial distribution of gray level data was evaluated using three sets of quantitative texture measures. These sets of texture parameters were extracted from the first order statistics (gray level histogram & Max-Min algorithm) and the second order statistics [run-length matrix and co-occurrence matrix].

The texture parameters were calculated for each region of interest using software written in the C programming language and developed in our laboratory.

The echocardiographic images were obtained using a 5.0 MHz phased-array biplane transducer mounted to the end of a 100 cm gastroscope interfaced to an ultrasound unit ( Diasonic^® [CFM 750]). The patient fasting overnight, his oropharynx was anesthetized with viscous and spray lidocaine to reduce (diminish) gagging, retching and laryngospasm during the procedure. Intravenous midazolam hydrochloride was given to reduce anxiety and provide sedation and amnesia for a modestly unpleasant procedure. A blood pressure monitoring and a pulse-oxymeter were also connected to the patient’s arm. The examination room was equipped with suction apparatus, oxygen, anesthesia bag, face mask and oral airway to face any emergency during the operation.

The patient lied on his left side, facing the examiner. This position reduces the possibility of aspiration. The patient’s head was comfortably flexed to facilitate oropharyngeal entry. With the probe in the mid-esophagus and slightly retroflexed, a four-chamber view of the heart could be obtained. All patients were mechanically ventiled.

During the echography exam, the probe was positioned to visualize the short axis-view of the left ventricle at the mid papillary muscle level. The use of the oesophagien way avoids the pulmonary parenchyma that could be an obstacle for the ultrasounds propagation. The images were acquired by using high ultrasound frequency and the probe was closed to the heart organ. Only the short axis view of the left ventricle at the mid-papillary muscle level was evaluated.

The acquisition based on transesophageal echocardiography allowed to visualize the structures of the heart with a good spatial resolution. The ultrasonic beam, in this case, did not find an obstacle to cross the thoracic wall. Images corresponding to end diastolic and end-systolic were then stored.

End-diastole was defined as the point in the cardiac cycle at the onset of the electrocardiographic R wave. End-systole was defined as the time of apparent minimal left ventricular chamber size and occurred near the peak of the T wave. One cardiac cycle (RR waves) was automatically divided into 12 frames independent of heart rate, and the images corresponding to the end-diastolic and end-systolic phases were selected with optimal visualization of the interventricular septum and left ventricular posterior wall.

For each frame of the short-axis view at end-diastole and at end-systole, four regions of interest (R.O.I.) were selected, manually using commercial software (L.U.I.S^® 1.01..), corresponding to the posterior, the anterior, the septal and the lateral walls of the left ventricular in both end systole and end diastole, including only the myocardium and excluding the endocardial and epicardial specular echoes to avoid areas of echo dropout and obvious artifacts. The selected echocardiographic images recorded on videotape were digitized offline by a frame grabber [Bioscan Snaphot^®, Washington]. The images selected to be treated were converted into frame of 512 x 512 pixels of 256 gray levels each [0 = black, 255 = white]. Each region of interest had 1cm² *size.

Segmental wall motion abnormalities related to myocardial contusion, were found out in the anterior wall in six patients, in the posterior wall in five patients, in the septal wall in seven patients and in the lateral wall in one patient.

Quantitative Texture Analysis [TA] on TEE. images provided information which could be useful for diagnosis aid of MC.

The TA was used on echographic images to accurately identify ischemic and contused myocardium in animal models [10Pandian NG, Skorton DJ, Doty DB, Kerber RE. Immediate diagnosis of acute myocardial contusion by two-dimensional echocardiography: study in a canine model of blunt chest trauma J Am Coll Cardiol 1983; 2: 488-96., 11Skorton DJ, Collins SM, Nichols J, Pandian NG, Bean JA, Kerber RE. Quantitative texture analysis in two dimensionel echography: Application to the diagnosis of experimental myocardial contusion Circulation 1983; 68: 217-3., 15Skorton DJ, Melton HE, Pandian NG, et al. Deletion of acute myocardial infarction in closed-chest dog by analysis of regional two-dimensional echocardiographic gray-level distributions Circ Res 1983; 52: 36-44.]. It has also been applied to identifying amyloid [14Frazee RC, Farnel MB, Miller FA. Objective evaluation of blunt cardiac trauma J Trauma 1986; 26: 510-20.], hypertrophic cardiomyopathies [17Chandrasekaran K, Aylward PE, Fleagle SR, et al. Feasibility of identifying amyloid and hypertrophic cardiomyopathy with the use of computerized quantitative texture analysis of clinical echocardiographic data J Am Coll Cardiol 1989; 13: 832-409.], myocarditis [18Lieback E, Hardoulin I, Meyer R. Clinical value of echocardiographic tissue characterization in the diagnosis of myocarditis Acoust Imaging 1996; 17: 22.] and myocardial ischemia [19Picano E, Faletra F, Marini C, et al. Increased echodensity of transiently asynergic myocardium in humans: a novel echocardiographic sign of myocardial ischemia J Am Coll Cardiol 1993; 21: 199-207.] or viable myocardium [20Marini C, Picano E, Varga A, et al. Cyclic variation in myocardial gray level as a marker of viability in man: a videodensitometric study Eur Heart J 1996; 17: 472-9.].

The aim of this approach is to characterize the stochastic proprieties of spatial distribution of the gray level of image. The statistical approach is used when the extraction of primitive and spatial organization is not evident. The ultrasound field is defined as a stochastic environment or quasi stochastic (micro-textures). The basic primitive is then reduced to the whole pixel or to one pixel which is named as the microscopic texture [27Amichi A. Importance of texure analysis in medical imaging: Apply to MRI and ultrasound images PhD Thesis, Parametric imaging laboratory: University Orsay Paris XI. 1998.]. The statistical approaches are the better and the adapted method to analyze the micro-textures tied to the stochastic distributions of echographic images.

Among these methods used :

In this study, it has been observed that the texture parameters extracted from gray level histogram in case of anterior, posterior, lateral and septal wall, do not disriminate between normal and contused myocardium.

In case of the anterior wall : the measurements of the short run-Lenght (SRE) in the horizontal direction were different between normal and contused myocardium (0.178 ± 0.021 versus 0.147 ± 0.020 respectively, p = 0.023, p < 0.05) at the end-diastolic.

In case of the posterior wall : the measurements of the variance (VAR) derived from the co-occurence matrix are different between normal and contused myocardium 4.66 ± 0.498 versus 2.482 ± 0.3339 respectively, p=0.023, p < 0.05] at the end-diastolic.

In case of the septal and the lateral wall, grouped on the same group, four texture features at the end-diastolic and two features at the end-systolic were different (p<0.05) between normal and contused myocardium as shown in Table 2.

Table 2

Texture Measures that Distinguished Normal from Contused Myocardium [p<0.05]

This observation is different from that reported by Skorton et coll [11Skorton DJ, Collins SM, Nichols J, Pandian NG, Bean JA, Kerber RE. Quantitative texture analysis in two dimensionel echography: Application to the diagnosis of experimental myocardial contusion Circulation 1983; 68: 217-3.], where eleven texture parameters derived from the second order statistics to the diagnosis of myocardial contusion. This study was used in the closed chest dog, using transthoracic echocardiography, before and after experimental contusion. This experimental approach is different from the routine echocardiography. Obviousely, discriminant texture features obtained from transthoracic echocardiography are different than the texture parameters obtained from transesophageal echocardiography. Echo amplitudes are influenced by transducer center frequencies used for this study (2.4 Mhz for transthoracic and 5 Mhz for transesophageal) [12Liedtke AJ, De Muth WE. Non penetrating cardiac injuries: a collective review Am Heart J 1973; 86: 687-97., 30Eaton MH, Lappas D, Waggoner AD, Pérez JE, Miller JG, Barzilai B. Ultrasonic myocardial tissue characterization in the operating room: initial results using transesophageal echocardiography J Am Soc Echocardiogr 1991; 4: 541-6.]. Gray levels is affected by instrument setting such as adjustment parameters, preprocessing, postprocessing curves, and the compression function [27Amichi A. Importance of texure analysis in medical imaging: Apply to MRI and ultrasound images PhD Thesis, Parametric imaging laboratory: University Orsay Paris XI. 1998.].

Skorton et coll found twelve texture features which are able to differentiate the normal from the contused myocardium [11Skorton DJ, Collins SM, Nichols J, Pandian NG, Bean JA, Kerber RE. Quantitative texture analysis in two dimensionel echography: Application to the diagnosis of experimental myocardial contusion Circulation 1983; 68: 217-3.]. Only one texture parameter was derived from the gray level histogram statistics (mean gray level). The others parameters were derived from the second order statistics.

In our study, none of the first order parameters was effective in differentiating normal and contused myocardium. Analysis of the gray level histogram (first order statistics) is an analysis of the overall distribution of echo amplitudes in an image, but cannot provide information on the spatial distribution of echo amplitudes. The number of discriminant parameters were limited and lacked the discriminating power.

It is observed that measurents of image gray level using second order statistics (Gray level run-lenght statistics and co-occurrence matrix), are capable to discriminate contused myocardium. It is also noted that the discrimaning texture parameters are different between regions of interest.