sixteen client - owned cats , presented to the irion animal hospital , seoul , korea , over a period of 7 months ( november 2014 may 2015 ) were included in the study . all of these cats were undergoing minor dental treatment , and all of owners of these cats 
 were voluntarily participated in this study . the mean age of cats was 3.8 years ( range 17 years ) with a mean body weight of 4.0 kg ( range 2.86.0 kg ) . all cats were considered clinically healthy except for dental disease , by the owners at the time of the 
 investigation , and this observation was supported by findings on physical examination , complete blood count , serum chemistry and thoracic radiography . after ct 
 examination , microscopic examination via tracheal washing was performed , and animal with suspected infectious condition was excluded . four asthmatic cats were selected from patients who have visited irion animal hospital from 2014 to 2015 , and they showed clinical signs of wheezing and 
 coughing , obvious bronchial and interstitial pattern in radiograph and therapeutic response to glucocorticoid . the mean age of cats was 7.8 years old ( range 511 
 years old ) with a mean body weight of 5.2 kg ( range 2.77.0 kg ) . four cats were 2 russian blue cats , 1 abyssinian cat and 1 domestic short hair cat . the animals 
 of both healthy group and asthmatic group were fasted approximately 8 hr for general anesthesia . , 
 seoul , korea ) was injected rapidly ( 6 mg/ kg , iv ) for induction . the tracheal tube was intubated , and anesthesia was maintained with isoflurane 
 ( ifran , hana pharm . heart rate , respiratory rate , body temperature and end tidal carbon dioxide ( etco2 ) were 
 monitored continuously during anesthesia . studies were performed with 4 channels ct scanner ( lightspeed plus , general electric medical system , san 
 francisco , ca , u.s.a . ) . ct power injector ( liebel - flarsheim , mallinckrodt , cincinnati , oh , 
 u.s.a . ) was used for control injection of iohexol ( omnihexol , korea united pharm . infused contrast media were 
 600 mg i / kg . single breathe hold technique was performed that airway pressure was maintained at 15 cm of water to the airway during the ct scan . computed 
 tomography was performed using hrct : 1.25 mm thick transverse images spaced 5 mm apart . the 
 gantry rotation time was 1 sec , tube potential was kv 120 , and tube current was mas 200 . analysis of dicom ct images was performed using a commercially viewing and analysis software ( spectra , infinitt healthcare co. , ltd . , all measurements were obtained on contrast enhanced transverse images , using moderately edge enhancing reconstruction algorithm at the lung window ( window 
 width=1,500 hounsfield unit ( hu ) , window level= 600 hu ) . bronchial lumen , entire bronchial diameter and adjacent arterial diameter were measured in four locations : the cranial part of left cranial , left caudal , right 
 cranial and right caudal lung lobes . the right middle lung lobe was excluded , because the bronchus of the right middle lung lobe was visible longitudinally in 
 transverse image . the caudal part of the left cranial lobe was also excluded due to lack of reproducibility and image quality . pulmonary artery , bronchial lumen and whole bronchial 
 diameter were measured for the entire hyper - dense region associated with wall and artery ( fig . 1.high resolution computed tomography image of the caudal lung lobe . whole transverse image ( a ) and magnified image ( b ) . the whole diameter ( thick white 
 arrows ) and internal diameter ( thin white arrow ) of caudal bronchus and the diameter of the adjacent pulmonary artery ( black arrow ) in transverse image were 
 measured . all measurements were tried to caliper bronchi or arteries that were mostly circular . however , if circular bronchus and artery were not identified , oval 
 bronchus and artery were measured for smallest diameters to avoid any effect of obliquity in determining the exact diameter . by measuring the overall bronchial 
 diameter , bronchial lumen and adjacent artery , a total of three values ( ba ratio , td ratio and ta ratio ) were calculated ( fig . the calculation of bronchial wall thickness was derived indirectly 
 from overall and luminal diameter of bronchus ( t=(d - l)/2 ) . ) . because the bronchial wall thickness had relatively small values than other values , directly measuring of bronchial wall thickness could be erroneous . therefore , wall thickness ( t ) was derived indirectly from overall ( d ) and luminal ( l ) diameter of bronchus ( t=(d - l)/2 ) . high resolution computed tomography image of the caudal lung lobe . the whole diameter ( thick white 
 arrows ) and internal diameter ( thin white arrow ) of caudal bronchus and the diameter of the adjacent pulmonary artery ( black arrow ) in transverse image were 
 measured . the calculation of bronchial wall thickness was derived indirectly 
 from overall and luminal diameter of bronchus ( t=(d - l)/2 ) . all calculations in statistical analyses were performed using non - commercial software ( r , the r foundation ) and commercial software ( spss 19 , spss inc . one way analysis of variation ( anova ) was performed to identify differences between each lobe ( cranial part of left cranial , left caudal , right 
 cranial and right caudal ) in healthy group . a welch two sample t - test was used to compare difference between male and female . a welch two sample t - test was used to compare difference between healthy group 
 and clinically asthmatic group . sensitivity , specificity , positive 
 predictive value and negative predictive value were calculated using the standard approaches at various cut - off ratios . for all statistical analyses , a p value of less than 0.05 was considered significant . sixty four bronchi and arteries were obtained from heathy 16 cats , and 16 bronchi and arteries were obtained from 4 asthmatic cats . in obtained image , ba ratio , the calculated indices from healthy cats and asthmatic cats are described at table 1table 1.mean of each index measured in clinically healthy cats and clinically asthmatic catshealthy groupasthmatic groupp - value(n=16)(n=4)ba ratio0.86  0.120.93  0.21p=0.24td ratio0.18  0.020.22  0.02p<0.05ta ratio0.25  0.050.37  0.06p<0.05ba ratio , bronchial lumen to artery ratio ; td ratio , bronchial wall to whole bronchial diameter ratio ; ta ratio , bronchial wall to artery ratio .. td ratio and ta ratio in asthmatic cats were significantly greater than those in healthy cats ( p<0.05 ) . but , ba ratio showed no 
 significant difference between asthmatic cats and healthy cats ( p=0.24 ) . there were no significant differences in td ratio and ta ratio between 
 each lobe . and , there were no significant differences in td ratio and ta ratio in either ages or gender . ba ratio , bronchial lumen to artery ratio ; td ratio , bronchial wall to whole bronchial diameter ratio ; ta ratio , bronchial wall to artery ratio . given these findings , a receiver operating characteristic curve ( roc ) of td ratio and ta ratio was created using the data from healthy group and asthmatic group 
 ( fig . 3fig . 3.receiver operating characteristic curve of the td ratio and ta ratio in cats with asthma and healthy cats . the both td ratio and ta ratio were significantly different from 0.5 ( p<0.05 ) . ) . the area under curve ( auc ) of td ratio was 0.869 , and auc of ta ratio was 0.945 . the both aucs of td ratio and ta ratio were significantly greater than 
 0.5 ( p<0.05 ) . cut - off ratio of 0.203 was best balanced with sensitivity 81.3% and specificity 81.3% in td ratio . cut - off ratio of 0.316 was 
 best balanced with sensitivity 87.5% and specificity 92.2% in ta ratio ( table 2table 2.result using various cut - off ratios to predict bronchial wall thickening in multiple indicescut - off ratiotptnfpfnsensspecppvnpvaccuracytd ratio0.19414432120.8750.67290.40000.9560.71250.20313521230.8120.81250.52000.9450.81250.20512531140.7500.82810.52170.9300.8125ta ratio0.3031555910.9380.8590.62500.98210.8750.3161459520.8750.9220.73640.96720.91250.3311160450.6880.9380.73330.92300.8875td ratio , bronchial wall to whole bronchial diameter ratio ; ta ratio , bronchial wall to artery ratio tp , true positive ; tn , true negative ; fp , false 
 positive ; fn , false negative ; sens , sensitivity ; spec , specificity ; ppv , positive predictive value ; npv , negative predictive value . ) . receiver operating characteristic curve of the td ratio and ta ratio in cats with asthma and healthy cats . solid line represents td ratio , and dotted line 
 represents ta ratio . the both td ratio and ta ratio were significantly different from 0.5 ( p<0.05 ) . td ratio , bronchial wall to whole bronchial diameter ratio ; ta ratio , bronchial wall to artery ratio tp , true positive ; tn , true negative ; fp , false 
 positive ; fn , false negative ; sens , sensitivity ; spec , specificity ; ppv , positive predictive value ; npv , negative predictive value . as a result , the td ratio and ta ratio in cats with asthma were significantly greater than those in clinically healthy cats . however , the ba ratio was not 
 significantly different between the healthy group and the asthmatic group . that is because , if the whole diameters of bronchi in feline asthma are the same , the 
 luminal diameters will be smaller due to bronchial wall thickening . if the ba ratio is measured in lesions , such as bronchiectasis , it is considered that ba ratio 
 may be different between asthmatic cats from healthy cats . the auc of td ratio had relatively high accuracy in predicting bronchial wall thickening in asthma patients , with a value of 0.869 . the auc of ta ratio was 
 0.945 , which was greater than that of td ratio . therefore , ta ratio is a more accurate index to detect bronchial wall thickening in asthmatic patients than td 
 ratio . the td ratio cut off value of 0.203 had the best balance of sensitivity and specificity , while the ta ratio cut off value of 0.316 had the best . therefore , 
 to determine the bronchial wall thickening in cats with asthma , ta ratio and cut - off threshold of td ratio could be used . several studies have evaluated the bronchial wall thickness in human medicine . since bronchial wall thickness can be changed according to airway generation , we 
 calculated the ratios of bronchial and arterial dimensions rather than their absolute values . one of the ratios was the td ratio which was dividing bronchial wall 
 thickness by the whole diameter of bronchus . the percentage of wall area ( wa% ) has also been used in the quantification of bronchial wall thickness in human 
 asthma patients . in the case of bronchiectasis , simple measurement of bronchial wall thickness divided by bronchial luminal diameter could cause spurious 
 underestimation of intrinsic bronchial wall thickening . thus , to obtain an estimation of bronchial wall thickness , we used ta ratio , which was the ratio of mean 
 bronchial wall thickness divided by mean diameter of the accompanying pulmonary artery used previously . as a result , we found that the ta ratio was more 
 accurate than td ratio . in human medicine , many studies have reported of correlation between the severity of asthma and images of bronchial changes in hrct . the forced expiratory volume 
 in one second ( fev1 ) has been reported to be correlated with wa% . td ratio and wa% have been reported to be negatively correlated with carbon monoxide transfer 
 coefficient . in veterinary medicine , bronchial wall thickness ratios will be helpful to assess the severity of feline asthma , because it is quantitative . however , indexing for the severity of asthma , such as fev1 , in human medicine has not been established in veterinary medicine . furthermore , the breed of cats used in this study was not diverse . therefore , it was difficult to 
 compare difference between breeds . research studies are needed to determine the differences in normal ranges of bronchial wall for a variety of feline breeds . for 
 example , in brachycephalic breed cat , such as persian cat , bronchial wall can be thicker than other breeds , even though there is no clinical sign . dogs with 
 brachycephalic airway syndrome may contribute to the loss of small airway wall rigidity . based on this finding , the ba ratio in brachycephalic breed dogs is 
 found to be different from that in non - brachycephalic dogs . in persian cat , brachycephalic syndrome including stenotic nares and elongated soft palate has 
 been reported . for the first time , this study reported the evaluation of bronchial wall thickness of normal cats and clinically asthmatic cats using hrct . our results suggest 
 that quantification indices of bronchial wall thickness , such as td ratio and ta ratio , can be used to diagnose feline asthma syndrome and other diseases 
 involving bronchial wall thickening . in conclusion , hrct is a useful modality to quantify bronchial wall thickness to diagnose diseases involving the thickening 
 of bronchial wall , including feline asthma .
the objective of study is to determine the thickness of bronchial walls of clinically diagnosed asthmatic cats using high resolution computed tomography ( hrct ) 
 compared to that of healthy cats . 
 the bronchial walls and pulmonary arteries were measured in healthy 16 cats and clinically asthmatic 4 cats . 
 the bronchial 
 walls and pulmonary arteries were measured under general anesthesia with positive pressure inspiration using hrct . in healthy and asthmatic cats , bronchial 
 lumen to the artery ratio ( ba ratio ) , the ratio of bronchial wall thickness to bronchial diameter ( td ratio ) and ratio of bronchial wall thickness to pulmonary 
 artery ( ta ratio ) were measured . 
 the mean ba ratio , td ratio and ta ratio in healthy cats were 0.86  0.12 , 0.18  0.02 and 0.25  0.05 , respectively . under the 
 same condition , the mean ba ratio , td ratio and ta ratio in asthmatic cats were 0.93  0.21 , 0.22  0.24 and 0.37  0.06 . 
 the td ratio and ta ratio in asthmatic 
 cats were significantly higher than healthy cats ( p<0.001 ) . 
 ba ratio was not significantly different in both groups 
 ( p>0.05 ) . 
 the evaluation of bronchial wall thickness by hrct could be useful for diagnosis of disease of bronchial wall thickening , such as 
 feline asthma .