Journal of Medical Imaging and Radiation Sciences

Journal of Medical Imaging and Radiation Sciences 41 (2010) 4-11

Journal de l’imagerie médicaleet des sciences de la radiation

www.elsevier.com/locate/jmir

Correlation of Exercise and Rest Tc-99m MIBI Lung/heart Ratio atDifferent Areas of Lung with Left Ventricular Ejection Fraction in Patients

with Coronary Artery Disease

Kanwal Afsheen, MBBS, MSca and Wazir Muhammad, MSc, MSb*a Department of Nuclear Medicine, Nuclear Institute of Medicine and Radiotherapy (NIMRA), Hyderabad, Sindh, Pakistan

b Department of Physics, Kyungpook National University, Daegu, Republic of Korea

ABSTRACT

Increased lung uptake of thallium-201 (201Tl) and technetium-99m-methoxyisobutyl isonitrite (99mTc-MIBI) in myocardial perfusionimaging has been proved as a reliable marker of left ventricular dys-function. The goal of this study was to evaluate the lung uptake at

the various areas of both the right and left lung (ie, right lung baseand both lung apices) and its correlation with the left ventricular dys-function by calculating lung-to-heart (L/H) uptake ratio in exercise

and rest 99mTc-sestamibi myocardial perfusion. There were a totalof 63 patients (10 female, 53 male: age range from 30–75 years,mean age 45.3 years, median age 45 years) with chronic coronary ar-

tery disease undergoing two-dimensional (2D) echocardiogram tocalculate left ventricular ejection fraction (LVEF). Planar imageswere taken before myocardial perfusion imaging to calculate the

L/H at different sites of the lungs. The patients having LVEF �40%on 2D echo (32 patients) were included in group A, and the patientshaving LVEF >40% on 2D echo (31 patients) were included ingroup B. The L/H differs significantly during stress and rest at the

selected lung areas (P < .05). The uptake ratio at the right lungbase was greater than the ratio at apices. In group A, L/H was signif-icantly higher during stress and rest as compared with group B.

However, in both the groups, stress uptake counts were greater ascompared with rest. A statistically significant inverse correlationwas found between the L/H uptake ratio and LVEF during exercise

and rest at both the lung base and apices. Useful clinical informationregarding left ventricular dysfunction was proved by L/H, irrespec-tive of the area selected at lung.

Both authors contributed equally to the work.

* Corresponding author: Department of Physics, Kyungpook National Uni-

versity, Daegu 702-701, Republic of Korea. Tel: (0082)10-3901-4141; Fax:

(0082) 53 952-1739

E-mail address: wazir90@hotmail.com (W. Muhammad).

1939-8654/10/$ - see front matter � 2010 Elsevier Inc. All rights reserved.

doi: 10.1016/j.jmir.2009.10.002

RESUME

Il a ete demontre que l’augmentation du captage du thallium-201(201Tl) et du technetium-99m-methoxyisobutyl isonitrite (99mTc-MIBI) en imagerie de perfusion myocardique constituait un marqueurfiable de dysfonction ventriculaire gauche. Le but de la presente etude

etait d’evaluer le captage pulmonaire en differents lieux des poumons(c’est-a-dire base du poumon droit et sommet des deux poumons) et lacorrelation avec la dysfonction ventriculaire gauche en calculant le ra-

tio de captage cœur-poumon (P/C) en perfusion myocardique au ses-tamibi marque au 99mTc. L’etude a porte au total sur 63 patients (10femmes et 53 hommes, ages de 30 a 75 ans, age moyen 45,3 ans, age

median 45 ans) presentant une maladie coronarienne chronique etsoumis a un echocardiogramme 2D afin de calculer la fraction d’ejec-tion ventriculaire gauche (FEVG). Des images planaires ont ete prises

avant l’imagerie de perfusion myocardique afin de calculer le C/P a dif-ferents sites des poumons. Les patients presentant une FEVG �40%en echographie 2D (32 patients) ont ete places dans le groupe A alorsque les patients presentant une FEVG >40% en echographie 2D (31

patients) ont ete places dans le groupe B. Le ratio P/C presente unedifference significative entre les mesures a l’effort et au repos dans leszones selectionnees des poumons (P < .05). Le ratio de captage a la

base du poumon droit (BPD) etait plus eleve qu’au sommet desdeux poumons. Dans le groupe A, le P/C etait plus eleve de facon sig-nificative au repos et a l’effort comparativement au groupe B. Dans les

deux cas cependant, le captage etait plus eleve a l’effort qu’au repos.Une correlation inverse statistiquement significative a ete constatee en-tre le ratio de captage P/C et la FEVG a l’exercice et au repos, a la basecomme aux sommets des poumons. Sans egard a la zone pulmonaire

selectionnee, le ratio P/C a permis d’obtenir des renseignements clin-iques importants concernant la dysfonction ventriculaire gauche.

Introduction

Coronary artery disease (CAD) is a complex disease in whichreduced or absent blood flow in one or more of the arter-iesdthose that supply blood to the heartdis usually ob-served. CAD is usually a degenerative disease and it isuncommon as a clinical problem before age 30, apart from

Figure 1. (a) Regron of Interest (ROI) was drawn and counts of myocardium were determined. (b) ROI drawn on myocardium was copied at the base of lung to

calculate the base counts. (c) ROI drawn on myocardium was copied at the apices of the lung to calculate the apices counts. (d) Heart to lung ratio was determined

by dividing the counts at the apices/base of lung by the counts of myocardium.

rare congenital abnormalities (birth defects). It is common byage 60 [1]. Pakistan contains the highest incidence of CADcompared with the other areas of the world. The most prev-alent risk factors for coronary artery disease in Pakistan arehypertension, diabetes mellitus, hypercholesteremia, physicalinactivity, and being older than age 40.

The severity of CAD can be defined by the technetium-99m (99mTc) sestamibi myocardial perfusion scintigraphy.There are many noninvasive cardiac parameters that can beused as prognostic markers, such as transient ischemic dilata-tion and perfusion defect size. Lung/heart (L/H) uptake ratiohas been proved as marker of severe and extensive coronary ar-tery disease both for the thallium and 99mTc sestamibi [2–5].Exercise causes increased left ventricular end-diastolic pres-sure, which leads to pulmonary edema. This interstitial wateris the cause of lung uptake. Thallium and technetium bothdiffer in kinetics. Thallium (201Tl) is a potassium analogueand its lung uptake is a dynamic process that tends to normal-ize within 18 minutes after stress [6]. 99mTc is retained withinthe cellular mitochondrial matrix [7] and has limited washout

Table 1

Lung to Heart Ratio at Different Area of the Lungs during Stress and Rest in Gro

RLB/H Stress RLB/H Rest LLA/H Stress

Maximum 0.69 0.68 0.57

Minimum 0.61 0.58 0.39

Mean 0.66 0.64 0.45

SD 0.024 0.027 0.038

RLB/H, right lung base-to-heart; LLA/H, left lung apex-to-heart; RLA/H, righ

deviation.

K. Afsheen and W. Muhammad/Journal of Medical Im

until 60 minutes after its injection [8]. This makes delayed ac-quisition possible after the administration of theradiopharmaceutical. However, sestamibi uptake 1 hour afterexercise shows poor sensitivity for the detection of severeCAD [9]; recent studies show that clinically importantwashout from the lungs occur in the patients imaged after60–120 minutes [10]. In addition, lung uptake in 201Tl and99mTc-sestamibi myocardial perfusion imaging has beenproven to predict left ventricular dysfunction.

Lung uptake for the thallium as well as the 99mTc-sestamibihas been proved for the noninvasive quantitative assessment ofthe left ventricular systolic function [2–5, 11–14]. However,the study was designed to assess the ability of predicting thelung uptake on different areas of the lung (ie, at apices and atright lung base) and their correlation with left ventricularejection fraction (LVEF) using the 99mTc-sestamibi MPSstudy. It was proved that the L/H ratio at the apices of thelung quantification of ejection fraction is also possible, andit also gives clinical information regarding left ventriculardysfunction.

up A

LLA/H Rest RLA/H Stress RLA/H Rest LVEF

0.52 0.53 0.51 40.00

0.38 0.39 0.37 27.00

0.43 0.45 0.44 35.19

0.038 0.036 0.038 3.922

t lung apex-to-heart; LVEF, left ventricular ejection fraction; SD, standard

aging and Radiation Sciences 41 (2010) 4-11 5

Table 2

Lung to Heart Ratio at Different Area of the Lungs during Stress and Rest in Group B

RLB/H Stress RLB/H Rest RLA/H Stress RLA/H Rest LLA/H Stress LLA/H Rest LVEF

Maximum 0.51 0.48 0.39 0.38 0.39 0.37 72.00

Minimum 0.40 0.38 0.29 0.27 0.30 0.27 45.00

Mean 0.44 0.42 0.33 0.32 0.34 0.33 61.48

SD 0.028 0.029 0.028 0.029 0.026 0.030 7.293

RLB/H, right lung base-to-heart; LLA/H, left lung apex-to-heart; RLA/H, right lung apex-to-heart; LVEF, left ventricular ejection fraction; SD, standard

deviation.

Materials and Methods

For the present study, 63 patients with CAD who wereregistered at the Karachi Institute of Radiotherapy and Nu-clear Medicine were selected (10 female, 53 male: age range30–75 years, mean age 45.3 years, median age 45 years).The inclusion criteria included the patients who were provenangiographically as CAD patients and who were able to un-dergo the exercise stress test. The patients having any respira-tory disease were excluded, and none of the patients wereactive smokers in the last 5 years. Of the 63 patients, 32were hypertensives and 32 were diabetics. Nineteen had a his-tory of myocardial infarction and 13 had had coronary arterybypass grafting. The multiple risk factors were not assessed in-dividually with lung uptake. The patients were suffering fromsingle vessel disease to triple vessel disease.

All patients underwent two-dimensional–echocardiogramfor determination of their LVEF before undergoing myocardialperfusion study. The patients were divided into two groups, Aand B, on the basis of their LVEF. The patients having LVEF�40% on two-dimensional echo (32 patients) were included ingroup A, and the patients having LVEF >40% on two-dimen-sional echo (31 patients) were included in group B [15]. Thepatients were advised to avoid heavy meals for at least 4 hoursprior and abstain from caffeine-containing drugs and bever-ages. They also withdrew any medications that could interferewith responses to a stress test such as b-blockers, calcium chan-nel, long-acting nitrates, and nitroglycerin; stopping 72, 48,24, and 1 hour previous, respectively [16].

The standard Bruce protocol was used by all patients whileexercising on a treadmill [5]. Both the stress and rest planner im-ages were performed on the same day in the study. The 1-daystudy protocol (with stress images performed earlier than restimages) was followed, because the patients with normal stressimages were excluded from the study. Electrocardiogram with12 leads every 1–3 minutes during the exercise was monitored

Table 3

Correlation Coefficient r and P Value between Lung to Heart Ratio at Different A

RLB/H

Stress R

A Correlation Coefficient (r) with LVEF �0.86 �P value <.05

B Correlation Coefficient (r) with LVEF �0.82 �P value <.05

RLB/H, right lung base-to-heart; LLA/H, left lung apex-to-heart; RLA/H, righ

6 K. Afsheen and W. Muhammad/Journal of Medical Im

[5], and blood pressure was also determined every minute dur-

ing exercise. The exercise was kept symptom-limited and was

terminated when the subject achieved 85% of the age maximumpredicted heart rate or a workload of at least 5 minutes [5]. A

compact bolus of 7 mCi of 99mTc-sestamibi was injected into

the intravenous line 1–2 minutes before the cessation of exercise

and flushed with 10 mL of normal saline [17]. The patients weremonitored frequently for abnormal change in blood pressure,

marked ST changes on the electrocardiogram, development of

serious arrhythmias, or severe chest pain. With developmentof angina, stress was discontinued and the reason was noted.

Planar images were obtained after 15–20 minutes of the

injection of 99mTc-sestamibi before the patient had breakfast

[10]. The patients underwent an image with a large field-of-view Gamma Camera (Siemens Single Head E-Cam)

equipped with a low-energy collimator and a photo peak set

at 140 keV with a 15% window [15]. The planar imageswere obtained with 800 kilo counts in the anterior projection

with camera as close as possible to the chest of the patient by

using a 128� 128 matrix format with a zoom of 1.8 [15].The patients were advised to have breakfast after the planar

images and before starting their single photon emission com-

puted tomography (SPECT) studies. Then, SPECT images

were acquired by using a 64� 64 matrix through a 180�

rotation, at an angular interval of 3� from right anterior obli-

que 45� to left posterior oblique 45�, and a 20-second acqui-

sition time per projection was used [15]. Reconstruction wasperformed by a standard back projection using a Hanning

Filter for a 64� 64 matrix image [15]. These transaxial

images were then reoriented in the short, vertical long, andhorizontal long axes of the left ventricle.

Four hours after the stress imaging, a compact bolus of

20 mCi 99mTc-sestamibi was injected into the intravenous

line and flushed with 10 mL of normal saline to ensure the uti-lization of the full dose to the patient [18]. The planar images

reas of the Lung in Group A and Group B

LLA/H RLA/H

est Stress Rest Stress Rest

0.72 �0.80 �0.72 �0.90 �0.80

<.05 <.05

0.82 �0.86 �0.80 �0.88 �0.78

<.05 <.05

t lung apex-to-heart; LVEF, left ventricular ejection fraction.

aging and Radiation Sciences 41 (2010) 4-11

Figure 2. Graph between right lung base-to-heart (RLB/H) ratios of stress and

left ventricular ejection fraction (LVEF) for group A.Figure 4. Graph between right lung apex-to-heart (RLA/H) ratio at stress and

left ventricular ejection fraction (LVEF) for group A.

were taken after 15–20 minutes of injection of 99mTc-sestamibi[10]. The SPECT images were also taken for the rest portion ofthe study after 1 hour of administration of the dose, but the lunguptake was not quantified for these images because planar im-ages taken early were considered superior for calculating lunguptake. All the images were corrected for background.

The heart and lung activities were quantified by manuallydrawing a region of interest (ROI) over the part of the myo-cardium with the maximal count density and copying thesame ROI over the part of the right lung base with the max-imal count density as shown in Figure 1(a-d). In this study,the early anterior planar images were used for the assessmentof L/H ratio [10, 19]. The right lung base-to-heart (RLB/H)ratio was calculated by dividing the counts in the lung ROI bythe counts in the heart ROI (Figure 1) [20]. In patients withsignificant ischemia, ROI was drawn on the heart, includingthe infarcted area. Previously, in all the studies, the lungROI was drawn on the left lung adjacent to the heart. Theright lung apex-to-heart (RLA/H) uptake ratio and left lungapex-to-heart (LLA/H) uptake ratio was also calculated (Fig-ure 1). ROI drawn at the base of right lung was copied atthe apices of both right and left lung and its ratio was deter-mined by dividing the counts at the apices of lung by the

Figure 3. Graph between right lung base-to-heart (RLB/H) ratios of rest and

left ventricular ejection fraction (LVEF) for group A.

K. Afsheen and W. Muhammad/Journal of Medical Im

counts of myocardium. The L/H ratios at base of right lungand at apices of both right and left lung (RLB/H, LLA/H,and RLA/H) were correlated with the ejection fraction. Pairedsample t-test was applied by using software SPSS version 14;on the LB/H, LLA/H, and RLA/H ratios, both at stress andrest, correlation coefficient (r) was also calculated betweenthe ejection fraction and L/H, LLA/H, and RLA/H ratiofor both groups A and B.

Results and Discussion

Echocardiography was performed and LVEF were calcu-lated for each patient. According the LVEF results, patientswere divided in groups A or B. Thirty-two and 31 patientswere in groups A and B, respectively. The minimum, maxi-mum, mean, and standard deviation (SD) was listed in Table1 and 2 for groups A and B, respectively. All patients under-went rest and exercise 99mTc-sestamibi myocardial perfusionimaging as part of their routine evaluation for CAD. RLB/H, RLA/H, and LLA/H ratios were calculated both after stressand rest after 99mTc-sestamibi injection by drawing the ROI

Figure 5. Graph between right lung apex-to-heart (RLA/H) ratio at rest and

left ventricular ejection fraction (LVEF) for group A.

aging and Radiation Sciences 41 (2010) 4-11 7

Figure 6. Graph between left lung apex-to-heart (LLA/H) ratio at stress and

left ventricular ejection fraction (LVEF) for group A.

Table 4

Correlation Coefficient between Right and Left Lung Apices to Heart Ratio

during Stress and Rest in Group A and Group B

Correlation Coefficient (r)

Stress Rest

Group RLA/H LLA/H RLA/H LLA/H

A 0.94 0.86

B 0.85 0.93

RLB/H, right lung base-to-heart; LLA/H, left lung apex-to-heart; RLA/H,

right lung apex-to-heart.

on the planar images. The ratios were correlated with the ejec-tion fraction. In group A, the mean of stress and rest RLB/Hratios were 0.66� 0.024 and 0.64� 0.027, respectively(Table 1); in group B, the mean of stress and rest RLB/H ratioswere 0.44� 0.028 and 0.42� 0.029, respectively (Table 2).In group A, the mean of stress and rest LLA/H ratios were0.45� 0.038 and 0.43� 0.038, respectively, and the RLA/H ratio at stress was 0.45� 0.036 and at rest was0.44� 0.038 (Table 1). In group A, RLB/H ratio after restinjection was significant in majority of the patients with theratio ranged from 0.58 to 0.68.

In group A, by comparing the L/H ratios of the stress andrest studies at different selected areas of the lungs (base andapices), a decreased trend was observed for apices as comparedwith the base of the right lung. For stress studies, the decreaseof mean value of RLB/H ratio with LLA/H and RLA/H ratiosis 21%, whereas the decrease of the mean value of RLB/H ra-tio with LLA/H and RLA/H radios are 23% and 22%, respec-tively, for rest study. For the same area (apices) on both rightand left lung, the decrease in RLB/H ratio at rest and stressstudies is not significant (within 1%). The ratio >0.47 wasconsidered as indication of exercise induced left ventriculardysfunction [13], but for the apices, the same limit may not

Figure 7. Graph between LLA/H ratio at rest and left ventricular ejection frac-

tion (LVEF) for group A.

8 K. Afsheen and W. Muhammad/Journal of Medical Im

be applied because the lower ratios at apices were observedfor higher ratio at base.

In group B, the stress and rest RLA/H ratio were0.33� 0.028 and 0.32� 0.029, respectively. The LLA/H ratioat stress is 0.34� 0.026, and, similarly, LLA/H ratio after restinjection gives a mean of 0.33� 0.030 (Table 2). Group A hada higher L/H ratio than group B during exercise and rest. Stressimages (after 15–20 minutes) in group A with ejection fractionof�40 show marked uptake of 99mTc MIBI and L/H ratio wassignificant. The RLB/H ratio ranged from 0.61 to 0.69 witha mean of 0.65 and standard deviation of 0.028 (Table 1).

In group B, the same decreased trend was observed for api-ces as compared with the base of the lung by comparing theL/H ratios of the stress and rest studies at different selectedareas of the lungs (base and apices). For stress studies, the de-crease of RLB/H ratio with LLA/H and RLA/H ratios are11% and 10%, respectively, whereas the decrease of RLB/Hratio with LLA/H and RLA/H ratios are 10% and 9%, respec-tively, for rest study. The decrease in L/H ratios at rest andstress studies is also not significant (1%) for group B for thesame areas (apices) on both right and left lung.

Paired sample t-test was applied on the RLB/H, LLA/H,and RLA/H ratios both at stress and rest and correlation co-efficient (r) was also calculated between the ejection fractionand RLB/H, LLA/H, and RLA/H ratios for both group Aand B (Table 3). No significant change was observed in the rvalue between the ejection fraction and for the L/H ratios of

Figure 8. Graph between right lung base-to-heart (RLB/H) ratios at stress and

left ventricular ejection fraction (LVEF) for group B.

aging and Radiation Sciences 41 (2010) 4-11

Figure 9. Graph between right lung base-to-heart (RLB/H) ratios at rest and

left ventricular ejection fraction (LVEF) for group B.Figure 11. Graph between right lung apex-to-heart (RLA/H) ratio at rest and

left ventricular ejection fraction (LVEF) for group B.

different lung areas (base and apices). While calculating r, sta-tistically significant inverse correlations were found betweenLVEF and the RLB/H ratio, LLA/H, and RLA/H ratios duringexercise (r¼ -0.86, -0.80, and -0.90 for RLB/H, LLA/H, andRLA/H ratios, respectively) and rest (r¼ -0.72, -0.72, and-0.80 for RLB/H, LLA/H, and RLA/H ratios, respectively)for group A (Figures 2–7). The same inverse correlation wasfound for both stress and rest studies in group B (Table 4, Fig-ures 8–13). The stress and rest RLA/H and LLA/H ratiosshowed inverse correlation with the LVEF irrespective of thelung area. It shows that there is no significant difference be-tween the uptake at the apices during either stress or rest.The P value (paired Student t-test) between uptake ratios dur-ing stress and rest was <.05 for group B; that is highly signif-icant. In addition, significant changes in the L/H ratio werefound in group A (P¼ .05) between exercise and rest notonly at the lung base, but also at the apices. In patients withthe higher ejection fraction, the uptake is less as comparedwith those with the lower ejection fraction that showed thatlung uptake can differentiate the patients with lower ejectionfraction (<40% group A) than those with higher ejection

Figure 10. Graph between right lung apex-to-heart (RLA/H) ratio at stress

and left ventricular ejection fraction (LVEF) for group B.

K. Afsheen and W. Muhammad/Journal of Medical Im

fraction (>40% group B). There is significant difference be-tween the uptake during stress and rest in both the groups ir-respective of the area drawn on the lung with the P value of<.05 between stress and lung uptake at both the apices andalso at the lung base. Mean lung uptake ratio was high inour studies as compared to some previous studies [5, 13,14]. The values of lung uptake at the apices are low as com-pared with the uptake at the base because of the increased vas-cularity at the base of the lung, and also from the effect ofgravity.

There is also another technical factord‘‘shine-through’’dto explain this result. Shine-through is a pitfallin the image evaluation; a portion of positron escaped fromthe source crosses the air-filled alveoli and annihilates at theopposite end, falsely suggesting activity at that location. Incase of 99mTc-sestamibi, there are no positrons, but activityfrom the hepatic area can shine-through and increase the ac-tivity measured in the lung base. Also, the vascularity in thelung base is denser; activity can accumulate in vessels and itcan shine-through from delayed clearance. When a ROI is ob-tained at the base of the lung, there is some significant shine-

Figure 12. Graph between left lung apex-to-heart (LLA/H) ratio at stress and

LVEF for group B.

aging and Radiation Sciences 41 (2010) 4-11 9

Figure 13. Graph between left lung apex-to-heart (LLA/H) ratio at rest and

LVEF for group B.

through phenomenon, which is much more important at thebase (more tissues) than at the apex (very little tissue). Uptakeratio at both the apices can differentiate the patients with thecompromised left ventricular function from those withthe higher ejection fraction. In group A when we compare thestress uptake at both the apices, it shows positive r value of0.94. This shows that the uptake at both the sides of thelung increases linearly, which shows a significant positive cor-relation (Table 4). The rest uptake at the apices also on boththe sides shows a positive r value of 0.86, which also showsa significant positive correlation (Table 4). Hence it wasproved that the ratio increased and decreased simultaneouslyat both sides of the lung.

The patients with more compromised ejection fractionshow an increase in the lung uptake after exercise. The differ-ence between the L/H ratio during stress and rest is mainlyrelated to the multiple risk factors, which were present inthe study (diabetics, hypertensives, post myocardial infarction,post-stenting, and post coronary artery bypass grafting). Therisk factors cannot be discussed separately because each ofthe patients was having multiple risk factors. The informationobtained from lung uptake can predict the possible myocar-dial event, left ventricular dysfunction, and CAD severity.In patients having either double vessel or triple vessel coronaryartery disease and also myocardial infarction, the lung uptakeis 0.67–0.68, which is comparatively higher. The majority ofthe patients who were having single vessel disease have left an-terior descending coronary stenosis, which has been alreadyassociated with ventricular dysfunction [20]. This increasein the ratio may be due to decreased myocardial activity ratherincreased lung activity [13]. The pharmacologic stress patientswere not evaluated in the study and the similar study for suchpatients can be designed. The lung uptake at the apices alsocorrelate with left ventricular dysfunction, but its associationwith myocardial event and CAD should be further sought.

Conclusion

In conclusion, the lung uptake quantification not only atthe lung base, but also at the apices, allows the identification

10 K. Afsheen and W. Muhammad/Journal of Medical Im

of patients with left ventricular dysfunction. Although thevalue of uptake at the apices is low as compared with the up-take at the base, statistically significant inverse correlation wasfound between the L/H and LVEF during exercise and rest atboth the lung base and apices. Useful clinical information re-garding left ventricular dysfunction can be provided by L/Hirrespective of the area selected at lung.

Acknowledgments

The authors would like to express their sincere thanks toDr. Maseeh-us-Zaman, head nuclear cardiology KIRANhospital Karachi, and Prof. Mudassir-ud-din, Departmentof Statistics University of Karachi, for their cordial help andcooperation during this study.

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