• Users Online: 119
  • Print this page
  • Email this page


 
 
Table of Contents
ORIGINAL ARTICLE
Year : 2020  |  Volume : 11  |  Issue : 2  |  Page : 70-75

Evaluation of clinico–Radiological profile and correlation with ultrasonography of the chest in coronavirus disease 2019 pneumonia


1 Department of General Medicine, SMS Medical College and Attached Group of Hospital, Jaipur, Rajasthan, India
2 Department of Radiodiagnosis, SMS Medical College and Attached Group of Hospital, Jaipur, Rajasthan, India
3 Department of General Medicine, SMS Medical College, Jaipur, Rajasthan, India
4 Department of Research Committee and Infectious Disease Prevention, SMS Medical College and Attached Group of Hospital, Jaipur, Rajasthan, India

Date of Submission01-Jun-2020
Date of Acceptance01-Jun-2020
Date of Web Publication07-Jul-2020

Correspondence Address:
Dr. Govind Rankawat
Department of General Medicine, SMS Medical College, Jaipur, Rajasthan
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/INJMS.INJMS_55_20

Rights and Permissions
  Abstract 


Background: The present study was undertaken to investigate imaging features of emerging coronavirus disease 2019 (COVID-19) pneumonia by chest ultrasound point-of-care ultrasonography (POCUS) and digital radiographs (chest radiograph [CXR]) and their correlation with clinical manifestation and severity of the disease. Methods: The present ongoing single-center study assessed patients admitted from April 20 to May 15, 2020, with laboratory-confirmed COVID-19 pneumonia at SMS Medical College Hospital, Jaipur, India. The clinical features, laboratory investigations, CXR, and POCUS findings were evaluated and compared. Results: Fifty-two patients with a manifestation of COVID-19 pneumonia were studied. Most of the patients were in the fifth and sixth decade of age group with a mean age of 56.57 years. There was an overall male preponderance (80% men and only 20% women). All pneumonitis patients were symptomatic with fever (88.46%), cough (82.69%), and dyspnea (55.77%) being the major symptoms. Thirty-four patients had underlying comorbid conditions. The digital radiograph-chest findings of 55.77% patients exhibited classic COVID-19 pneumonia findings. The ultrasonography of the chest findings revealed pleural and lungs changes in 94% of patients with COVID-19-positive pneumonia. CURB-65 score for the severity of pneumonia had a positive correlation with POCUS severity score and CXR visual score with P = 0.0013 and 0.0018, respectively. The duration of some major symptoms for COVID-19 pneumonia also had a positive correlation with the POCUS severity score and CXR visual score. Conclusion: The spectrum of COVID-19 pneumonia has a predilection for advancing age and male gender. Although both POCUS and CXR are important tools to detect severity of pneumonia, POCUS has higher sensitivity as compared to that of CXR to detect characteristics of COVID-19 pneumonia, especially interstitial involvement or acute respiratory distress syndrome.

Keywords: Clinico-radiological, coronavirus disease 2019, CURB-65, point of care ultrasonography


How to cite this article:
Bhandari S, Singh A, Bagarhatta M, Rankawat G, Dube A, Kakkar S, Tak A. Evaluation of clinico–Radiological profile and correlation with ultrasonography of the chest in coronavirus disease 2019 pneumonia. Indian J Med Spec 2020;11:70-5

How to cite this URL:
Bhandari S, Singh A, Bagarhatta M, Rankawat G, Dube A, Kakkar S, Tak A. Evaluation of clinico–Radiological profile and correlation with ultrasonography of the chest in coronavirus disease 2019 pneumonia. Indian J Med Spec [serial online] 2020 [cited 2023 Mar 31];11:70-5. Available from: http://www.ijms.in/text.asp?2020/11/2/70/289146




  Introduction Top


Coronavirus disease 2019 (COVID-19) is a pandemic infectious disease caused by a novel coronavirus, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 genome is similar to that of SARS and Middle East respiratory syndrome.[1] Infection by COVID-19 can result in a range of clinical outcomes, from asymptomatic to severe life-threatening course or death. Most of the afflicted patients present with high temperature and dry cough.[2] The diagnostic armamentarium of COVID-19 is inclusive of travel history, history of exposure, clinical features, and reverse transcriptase–polymerase chain reaction (RT-PCR) assay from specimens obtained by oropharyngeal or nasopharyngeal swab, assisted with ancillary workup of ultrasound (US), digital Chest radiograph (CXR), and computed tomography (CT).[3] point-of-care ultrasonography (POCUS) is a new tool in the assessment of the lungs as it scans and examines 14 categorical zones of the lungs (so segregated) and can be performed quickly and easily in critically ill patients (at bedside) and also can be repeated to assess deterioration/recovery. The present study was designed to systematically image lungs through POCUS and compare its sensitivity with that of digital CXR and to evaluate the association, if any, of findings of POCUS with that of clinical manifestations and severity of disease in such patients.


  Methods Top


Study design

The present descriptive, retrospective analysis was done on 52 patients of pneumonia with laboratory-confirmed RT-PCR for COVID-19 admitted in SMS Medical College Hospital, Jaipur, India, from April 20 to May 15, 2020. Our institutional review board approved this retrospective study. The data used were anonymized to protect the privacy and confidentiality of participants. The patients were examined clinically and were assessed for duration of symptoms, comorbid conditions, and severity of pneumonia. All patients underwent a digital CXR examination upon admission along with POCUS. Pneumonia was defined as an acute respiratory tract illness such as fever, cough, sore throat, dyspnea, and chest pain with radiographic pulmonary shadowing which was diffuse or segmental. Patients presented with clinical features of respiratory tract infection with radiographic pulmonary shadowing were included in the study group, while patients with normal CXR or asymptomatic were excluded from the study group. The 6-point CURB-65 scale was calculated to assess the severity of pneumonia[4] (CURB-65: confusion: 1; blood urea nitrogen > 20 mg/dL: 1; respiratory rate >30/min: 1; systolic blood pressure <90 mmHg or diastolic blood pressure <60 mmHg: 1; and Age >65 year: 1).

Data collection

The diagnosis of COVID-19 was made based on the World Health Organization interim guidance, wherein confirmed cases denoted patients whose RT-PCR assay findings for nasal and pharyngeal swab specimens were positive for SARS-CoV-2.[5] The epidemiological data of COVID-19 pneumonia patients were recorded inclusive of recent exposure history, clinical symptoms with duration, and comorbidities. A detailed clinical evaluation was done. Routine biochemistry and hematologic evaluation were performed.

Image acquisition

Taking into account the infectivity profile of COVID-19, dedicated image scanners inclusive of digital radiograph and ultrasonography (USG) lung scan specific machine with linear and convex probes were employed for such patients observing strict disinfection protocol both for health-care workers and patients as laid down by regulatory bodies.[6]

Digital chest radiograph

It was acquired and images were evaluated for presence and distribution of the following image abnormalities inclusive of ground-glass opacity (GGO), consolidation, cavity, and nodular pattern with their respective distribution being central, peripheral, apical, or basal.[7] The presence of lymphadenopathy, pleural effusion, and underlying lung disease (chronic obstructive pulmonary disease [COPD], interstitial lung disease, and pulmonary tuberculosis) was evaluated and severity score was recorded accordingly. The scoring pro forma was drawn on the said variables and observations were documented as normal (no findings on CXR but COVID-19 positive), classic/probable COVID-19 (basal and peripheral predominant, multiple, bilateral, ground glass haziness), indeterminate (does not satisfy criteria for classic or non-COVID-19 conditions), and non-COVID-19 (inclusive of pneumothorax, pleural effusion, and pulmonary edema). A severity score of CXR based on visual assessment of the overall area of lung involvement was assessed[8] [Table 1]. Observation of CXR correlated with duration of major symptoms, POCUS, and severity of disease (CURB-65 score).
Table 1: Severity score of chest X-ray based on visual assessment of overall area of lung involvement

Click here to view


POCUS imaging was done on 14 selected lung zones inclusive of two anterior (below and above the intermammary line in mid-clavicular plane), two lateral (upper and lower in mid-axillary line), and three posterior (upper, middle, and lower in mid-scapular line) on each side. POCUS of the lungs was performed in all cases (100%). Serial images and video clips (of 10 s) were saved. The following findings on POCUS imaging were taken as positive, namely thickening of pleural line with irregularity or indentation or broken pleural line, effacement of A-lines that are horizontal lines deep to pleural line as observed in normal lungs morphology on USG, appearance of B-lines (multiple hyperechoic lines, like laser beams) that could be thin, thick, multiple, or confluent leading to white out lung and obliterating A-line as observed in acute respiratory distress syndrome (ARDS), the appearance of small sub-pleural consolidation adjacent to broken pleural line, large area of consolidation with air bronchogram, minimal pleural effusion, and appearance of A-line during recovery phase.[9] The observations of sonographic lung scans were correlated with duration of major symptoms, severity of disease (CURB-65), and CXR scan. A scoring system has been devised to assess severity of lung involvement in POCUS [Table 2]. A metered reporting format was used to enter findings of POCUS in 14 different zones so examined, and subsequently, POCUS findings were classified on sliding scoring scale of severity on basis of these 14 zone severity scores ranging from a minimum = 0 to maximum = 42, and consequently, based on said sliding score scale, the lung involvement can be categorized as mild (with a score below 14), moderate (with a score between 14 and 28), and severe (with a score of more than 28).
Table 2: Scoring system to assess severity of lung involvement in pneumonia by chest ultrasound

Click here to view


Statistical analysis

The descriptive statistics for quantitative data was expressed as mean and standard deviation and qualitative data was expressed as proportions. After appropriate assumption checks, bivariate correlation (“'r” value) and P value were estimated between various quantitative variables. Correlation represents linear relationship between variables. To estimate the association between qualitative variables, coefficient of contingency (C) was estimated. The value of “C” varies from 0 to 1 (for infinite number of classes). There is no strength of association when the coefficient of contingency is 0 (C = 0). Statistical significance was tested with Chi-square tests at 5% level of significance. JASP Team (2020). JASP (Version 0.12.2)[Computer software]. University of Amsterdam, Netherlands Copyright 2013-2019.


  Results Top


Retrospective data from COVID-19 pneumonia patients were collected, evaluated, interpreted, and correlated with each other. Fifty-two patients (42 men and 10 women) with manifestation of pneumonia were admitted in SMS Medical College Hospital, Jaipur. Men constituted 78% of the sample population. Most of the patients (79%) were above 50 years of age with a mean age of patients is 56.5 years (95% confidence interval [CI]: 56.57 ± 2.72, standard deviation [SD] = 10.03). Pneumonitis patients were symptomatic and presented with chief complaints of fever (88.46%), cough (82.69%), dyspnea (55.77%), headache (32.69%), vomiting (13.46%), drowsiness (9.62%), chest pain (7.69%), arthralgia (5.77%), and hemoptysis (3.85%) [Table 3]. Thirty-four patients (65%) had underlying comorbid conditions of either hypertension (21.15%), diabetes mellitus (19.23%), coronary artery disease (15.38%), chronic obstructive pulmonary disease (11.54%), and pulmonary tuberculosis (9.62%). The severity of pneumonia in all COVID-19-infected patients was measured by the predesigned CURB-65 score with an average score found to be 1.07 (95% CI: 1.09 ± 0.255, SD = 0.93). In our study, 32.69% of the patients had CURB-65 score 0, another 32.69% patients had score 1, 28.85% patients had score 2, while remaining 5.77% patients had a score of 3. Twenty-nine patients (55.77%) on CXR had classic COVID-19 pneumonia findings of bilateral, multiple, peripheral, and lower zone predominant area of GGOs [Figure 1], 38.46% patients had indeterminate findings of discrete lobar pneumonia and hilar enlargement, and 5.77% had non-COVID CXR findings. POCUS of the chest was performed on all patients. USG chest scan documented pleural and lungs involvement in 94% of COVID-19 pneumonia patients [Figure 2], with sliding score scale categorizing 44% of patients afflicted with mild, 39% moderate, and 17% severe disease process with a mean USG severity score being 16.69 (95% CI: 16.69 ± 3.11, SD = 11.69).
Table 3: Clinical, comorbid, radiographic features, and CURB-65 score of coronavirus disease 2019 pneumonia

Click here to view
Figure 1: Chest X-ray of three different patients of coronavirus disease 2019 pneumonia presented with cough, fever, shortness of breath (SOB), and decreased oxygen saturation. (a) Classical bilateral basal and peripheral opacities with obscured right CP angle, (b) Bilateral, peripheral, ground-glass opacities with right side predominant, (c) Indeterminate for coronavirus disease 2019 have peripheral and central involvement with spared right basal zone

Click here to view
Figure 2: A 55-year-old male patient presented with complaints of fever, cough, SOB, and hemoptysis. Chest X-ray have classic coronavirus disease 2019 pneumonia, ultrasonography chest show typical findings of coronavirus disease 2019. (a) Thickened, irregular pleura, subpleural consolidation, pleural effusion and thick B-lines in the right basal lateral zone of the chest. (b) Broken pleural line, small subpleural consolidation and thick B-lines in left basal posterior zone of the chest. (c) Indented pleural line with thick B-lines in the right upper posterior zone of the chest

Click here to view


About 17% of the patients (9 of 52) of COVID-19 pneumonia had minimal pleural effusion without any underlying other identifiable cause [Figure 2]a. The radiological scoring (POCUS severity score and CXR visual score) was compared with the severity of pneumonia (CURB-65). A positive correlation was noted between POCUS severity score and CURB-65 score (r = +0.4331, P = 0.0013), CXR visual score and CURB-65 score (r = +0.4227, P = 0.0018), and POCUS severity score and CXR visual score (r = +0.7325, P < 0.001) [Table 4]. The duration of major symptoms of COVID-19 pneumonia was also compared with the radiological scoring system. We found a positive correlation between the duration of symptoms and radiological scoring system. POCUS severity score showed statistically significant correlation with the duration of cough (r = +0.4742, P = 0.0011) and dyspnea (r = +0.4718, P = 0.0097), while CXR visual score showed statistically significant correlation with only duration of dyspnea (r =+0.608, P = 0.0004). Prevalence of two major clinical features that is cough and dyspnea was noted significantly higher in patients who achieved more score on POCUS with P = 0.0065 and 0.0145, respectively. The POCUS scan documented basal involvement in 88% of sample COVID-19 pneumonia patients, of which 93% typically had posterior basal lung involvement [Table 5]. The POCUS scans document focal B lines as the main characteristic feature of an early stage of disease (patients with lesser duration of symptoms) with mild clinical symptoms.
Table 4: Comparison between radiological scoring system and duration of symptoms in patients of coronavirus disease 2019 pneumonia

Click here to view
Table 5: Chest zone affection by coronavirus disease 2019 pneumonia as detected by 14-zone ultrasonography chest

Click here to view



  Discussion Top


The dread and specter of COVID-19 made its first appearance in Wuhan, China, in the month of December 2019 and it has spread like wildfire out and across precincts of China across the globe with a pace that has taken everyone by surprise. Confirmed cases of COVID-19 are being reported from all corners of the world, and subsequently, the World Health Organization officially declared COVID-19 a pandemic on March 11, 2020.[10]

In a setting of high clinical suspicion of characteristic typical clinical symptoms with a history of previous exposure to individuals with confirmed RT-PCR SARS-CoV-2 diagnosis, a combination of chest imaging elements and repeat laboratory RT-PCR protocol could help to increase the chances of diagnosing COVID-19 with certitude. Subsequently, imaging pattern of COVID-19 pneumonia might be used for early detection of lung involvement and categorized patients according to their severity for definitive management. In the present study, multimodality imaging hallmarks of 52 patients with laboratory-confirmed COVID-19 features and clinico–radiographic pneumonia were evaluated during the initial phases of the disease, and it was observed that COVID-19 pneumonia most commonly affects the old age population (>50 years of age) with men getting affected more than women. COVID-19 pneumonia patients presented primarily with cough, fever, and dyspnea as predominant symptoms, though other symptoms such as headache, vomiting, drowsiness, and hemoptysis were present in some patients. COVID-19 pneumonia was more common in patients with underlying comorbid conditions such as hypertension, diabetes mellitus, coronary artery disease, COPD, and pulmonary tuberculosis. The salient features of classic COVID-19 findings of bilateral, multiple, peripheral, and lower zone GGOs on CXR could be appreciated in nearly half of the patients (55.77%), and the remaining sample population exhibited increased hazy opacities suggestive of indeterminate COVID-19 pneumonia and few of them had non-COVID manifestation of pneumonia. It has been observed and documented by Ng et al.[11] that CXR lacks sensitivity in diagnosing and picking up COVID-19 early in its disease course of afflicting the lungs. Lung USG was performed on all patients and various features of thickened/irregular/indented/broken pleura and subpleural consolidation with diffuse B lines (multiple/confluent/white out lung) and A-lines could be appreciated. Fourteen zones of the POCUS chest scan also detected COVID-19 pneumonia with a distribution primarily in the posterior–basal segments of the lungs. The severity and course of COVID-19 infection could be detected through POCUS scan, and the results correlated with clinical symptoms with their duration, severity of disease, and CXR findings. Subsequently, a lung USG scan could be an integral part of management protocol of SARS-CoV-2-positive patients with pneumonia giving the requisite framework for rapid diagnosis and regular monitoring of COVID-19 pneumonia and its antecedent probable evolution into ARDS in critically ill patients. The pulmonary lesion of bilateral and multifocal lung involvement as documented by POCUS lung scan has also been detailed by previous studies.[9] The severity of pneumonia as documented by CURB-65 score system had found a positive correlation with lung involvement in terms of radiological scoring system. We have also tried to find a correlation between the duration of major symptoms and radiological scoring system, and we found that the duration of symptoms had positive correlation with POCUS severity score and CXR visual score. Among major symptoms of COVID-19 pneumonia, cough and dyspnea had a significant positive correlation with POCUS severity score, while only dyspnea significantly correlated with CXR visual score. The advantages of employing POCUS scan in COVID-19-positive pneumonia patients are its ease, efficacy, sensitivity, and reliability in rapid assessment of severity (and its score) of disease process at bedside at the time of admission that CXR may fail to detect [Figure 3] and document in early stages of lung involvement that may not show typical findings in the early stage of disease. Moreover, POCUS scan has the added advantage of being admissible in pregnant women as well. POCUS is also helpful to differentiate non-COVID-19 pulmonary shadows detected by CXR from COVID-19 findings [Figure 4]. The limitation of USG is that strict guidelines have to be followed before and after examination for the person and machine to prevent the spread of infection. The validity of USG severity scoring system requires larger studies.
Figure 3: A 60-year-old male of coronavirus disease 2019 pneumonia admitted with complaints of fever and cough, (a) Chest X-ray shows indeterminate findings (no classical coronavirus disease 2019 findings). (b) Ultrasonography chest show features of coronavirus disease 2019 pneumonia that is broken pleural line, subpleural consolidation, and confluent B-lines

Click here to view
Figure 4: A 55-year old male known case of chronic obstructive pulmonary disease and pulmonary tuberculosis admitted with cough, fever and positive coronavirus disease 2019 test. (a) Chest X-ray shows bilateral, diffuse, multiple, patchy consolidation. (b) Ultrasonography of the chest of the same patient showing broken pleura, collapse/consolidation, and A-line (resolved pneumonia) without B-lines suggest that there is no active coronavirus disease pneumonia

Click here to view



  Conclusion Top


In the ongoing pandemic, we have used POCUS in patients diagnosed with COVID-19 pneumonia. The application of POCUS has allowed for identification of patients with lung involvement and severity. POCUS can detect the severity of COVID-19 pneumonia. COVID-19 pneumonia primarily and predominantly involves posterior–basal zone of the lungs, detectable with a high level of sensitivity by USG chest that could be used to prognosticate and serially corroborate with clinical pattern. POCUS is also helpful to differentiate non-COVID-19 pulmonary shadows detected by CXR from COVID-19 findings.

Limitations

The limitations of the study include its small sample population size with a lack of follow-up. A serial POCUS USG lung scan follow-up would have indeed given the time-course and evolutionary characteristics of COVID-19 pneumonia.

Acknowledgments

I want to give special thanks to Dr. C. L. Nawal, Dr. S. Banerjee, Dr. Prakash Keswani, Dr. Abhishek Agrawal, Dr. Vishal Gupta, Dr. Vidyadhar Singh, Dr. Dileep Wadhwani, Dr. Kapil Gupta, Dr. Jitendra Gupta, and Dr. Sunil Mahavar and team Department of General Medicine, SMS Medical College Hospital, Jaipur, for their valuable support.

Financial support and sponsorship

None.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Rothan HA, Byrareddy SN. The epidemiology and pathogenesis of coronavirus disease (COVID-19) outbreak. J Autoimmun. 2020;109:102433. doi:10.1016/j.jaut.2020.102433.  Back to cited text no. 1
    
2.
Guan WJ, Ni ZY, et al. China Medical Treatment Expert GroupforCovid-19, Clinical Characteristics of Coronavirus Disease 2019 in China, N. Engl.J. Med.(2020), https://doi.org/10.1056/NEJMoa2002032.   Back to cited text no. 2
    
3.
Zu ZY, DiJiang M, Xu PP, Chen W, Ni QQ, Lu GM, et al, Coronavirus Disease2019(COVID-19):A Perspective from China, Radiology(2020)200490, https://doi.org/10.1148/radiol.2020200490.  Back to cited text no. 3
    
4.
Lim WS, van der Eerden MM, Laing R, Boersma WG, Karalus N, Town GI, et al. Defining community acquired pneumonia severity on presentation to hospital: An international derivation and validation study. Thorax 2003;58:377-82.  Back to cited text no. 4
    
5.
World health organization Laboratory testing for coronavirus disease (COVID-19) in suspected human cases Interim guidance 19 March 2020, 1-7.  Back to cited text no. 5
    
6.
HICC, AIIMS, New Delhi Infection, Prevention &Control Guidelines for 2019-nCoV (COVID-19) Version 1.2 26 March 2020. 1-25.  Back to cited text no. 6
    
7.
Hansell DM, Bankier AA, MacMahon H, McLoud TC, Müller NL, Remy J. Fleischner Society: Glossary of terms for thoracic imaging. Radiology. 2008;246:697-722. doi:10.1148/radiol.2462070712.  Back to cited text no. 7
    
8.
Warren MA, Zhao Z, Koyama T, Bastarache JA, Shaver CM, Semler MW, et al. Severity scoring of lungs oedema on the chest radiograph is associated with clinical outcomes in ARDS. Thorax. 2018;73:840-6. doi:10.1136/thoraxjnl-2017-211280.  Back to cited text no. 8
    
9.
Peng QY, Wang XT, Zhang LN, Chinese Critical Care Ultrasound Study Group (CCUSG). Findings of lung ultrasonography of novel corona virus pneumonia during the 2019-2020 epidemic. Intensive Care Med 2020;46:849-50. doi:10.1007/s00134-020-05996-6.  Back to cited text no. 9
    
10.
Coronavirus (COVID-19) events as they happen (n.d.). https://www. who.int/emergencies/diseases/novel-coronavirus-2019/events-as-they happen [Last accessed on 2020 Mar 20].  Back to cited text no. 10
    
11.
Ng MY, Lee EYet al. Imaging profile of the COVID 19 infection: Radiologic findings and literature review. Radiol Cardiothorac Imaging 2020;2; e200034. https://doi.org/10.1148/ryct.2020200034  Back to cited text no. 11
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


This article has been cited by
1 CLINICO RADIOLOGICAL CORRELATION IN COVID-19 PATIENTS.
Bhanu Rekha Bokam, Sireesha Puvvadi, K.charan Lakshmi
INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH. 2022; : 17
[Pubmed] | [DOI]
2 Lung Ultrasound Predicts Clinical Severity of COVID-19 Pneumonia
Ashish Bhalla,Arun Sharma,Navdeep Kaur,Mandeep Garg,Neeti Dogra,Goverdhan D Puri,Rajarajan Ganesan,Karan Singla,Subhrashis G Niyogi,Alisha Goel,Narender Kaloria,Vighnesh Ashok,Nischitha Gowda,Varun Mahajan,Sujitha R Karri
Journal of Perioperative Echocardiography. 2019; 7(2): 28
[Pubmed] | [DOI]



 

Top
 
  Search
 
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

 
  In this article
Abstract
Introduction
Methods
Results
Discussion
Conclusion
References
Article Figures
Article Tables

 Article Access Statistics
    Viewed3878    
    Printed162    
    Emailed0    
    PDF Downloaded403    
    Comments [Add]    
    Cited by others 2    

Recommend this journal