Pulmonary nodule size evaluation with chest tomosynthesis and computed tomography: a phantom study

Transcription

1 Pulmonary nodule size evaluation with chest tomosynthesis and computed tomography: a phantom study Poster No.: C-1884 Congress: ECR 2014 Type: Scientific Exhibit Authors: S. S. Shim 1, Y. Kim 1, Y. W. Oh 1, K. Y. Lee 2, Y. J. Ryu 1, M. Lee 1 ; 1 2 Seoul/KR, Ansan/KR Keywords: DOI: Thorax, CT, Digital radiography, Computer Applications-Detection, diagnosis, Image verification /ecr2014/C-1884 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 21

2 Aims and objectives Solitary lung nodule detection has increased due to the widespread use of computed tomography (CT) imaging. Nevertheless, the most commonly used routine examination for lung nodule continues to be the chest radiographs as it uses low radiation doses, is economical, and easy to use. Since chest radiographic images are two-dimensional projections of three-dimensional structures, early lung cancer detection on chest radiographs is often challenging. The projection of pulmonary vessels, bones and part of the mediastinum on lung fields often partially or completely obscure the pulmonary nodules, resulting in a failure by the radiologist to detect lung nodules [1-2]. Digital tomosynthesis (TOMO) has recently been applied to chest imaging for the detection of subtle nodules on simple radiography, with promising results [3-4]. It has been introduced as a modality with the potential to provide an image comparable to CT, but with a comparably reduced cost and radiation exposure [4]. Dobbins et al. reported that 74% of lung nodules equal to or greater than 4mm that can be identified on CT can be detected using TOMO [5]. Vikgren et al. reported that 92% of these sized nodules are detectable using TOMO [6]. In 2012, Johnsson et al. compared the detection capability by nodule size of the two methods [7]. Their reported results of 20 patients found interchangeable measurement usage from TOMO and CT in follow-up pulmonary nodules. This result calls for caution as the limit of agreement (LOA) between the modalities is wider than the LOA for the intra-observer variability of each modality. Based on these studies, we hypothesized that TOMO imaging is comparable to CT imaging for the detection of nodules located in areas where size measurement is limited using simple chest radiography. Thus, we proposed to locate phantom nodules of various sizes in six lung zones wherein evaluation is limited. The purpose of this study was to assess the measurement of the size of nodules located in these zones by TOMO and chest CT. Methods and materials Thorax phantom and model nodule preparation Thorax phantom N1 (Kyoto Kagaku Co, Kyoto, Japan; materials: soft tissue and vessels are constructed of synthetic materials; i.e., polyurethane epoxy resin and calcium carbonate) was used. Model nodules witha homogenous composition of solid-type urethane foam nodules, of four sizes; 3, 5, 8, and 10 mm were used. Nodules was placed in six lung zones: the right apex; the middle of the right subpleural lung parenchyme; right upper hilum; right lower hilum; right diaphragmatic angle of the heart (right cardiophrenic angle); and the right lower retro-hepatic lung parenchyme. Page 2 of 21

3 Chest CT scan A total of 48 phantom sets, composed of four nodule size types, six locations, and two imaging modalities were included in this study. We used a 64-channel CT scanner (SOMATOM Definition scanner; Siemens Medical Systems, Forchheim, Germany) for chest computed tomography. The scanning parameters were as follows: individual detector width, mm; gantry rotation time, 0.5sec; tube voltage, 120 kvp; tube current, 30mAs; and pitch, 1. Axial images were reconstructed using 2-mm section thickness. Digital TOMO TOMO examinations were performed using a commercially available unit (Sonialvision Safire II, SIMADZE, Kyoto, Japan) with a #at-panel detector system. We altered the digital TOMO parameters to establish a lower radiation dose condition suitable for chest imaging. Seventy-four low-dose projection images were acquired within 4.85s using a tube voltage of 120 kvp and 0.04mAs. The detector was #xed into position, whereas the x-ray tube was subjected to vertical continuous movement, from -20 to +20, around the standard orthogonal posteroanterior position and image data were acquired. A total of 74 projection images were obtained from one examination and were used to reconstruct 84 coronal images with a thickness of 2 mm without overlap. Radiation dose For the radiation dose assessment in the TOMO, the dosimeter (Dosimeter: UnforsThinX Intra, Billdal, Sweden) attached to the center and the surface of the chest phantom (N1, Kyoto Kagaku Co, Kyoto, Japan) recorded the absorption dose. The absorbed dose at the phantom surface for TOMO was 0.7mGy, and the absorbed dose at the phantom center was 0.2mGy. Pulmonary nodule measurement Four radiologists with 15, 4, 3 and 1 years of experience in chest image interpretation participated in the study. A total of 48 images comprising nodules of four sizes in six different locations (Fig. 1) arranged in a random order by the ViewDEX software were used. Observers were blinded to the location and size of the nodules in the phantom model. They measured the left-to-right diameter, and recorded the longest length on TOMO and CT (Figs. 2-5). The use of the zoom or enlarge tool was freely available, and the window levels for CT were from -400 to 1200H, while for TOMO they were H. These values are clinically relevant. All measurements were repeated at 20-day intervals to assess intraobserver variation. Statistical analysis Nodule size measurement errors for measurement on TOMO and CT images compared with actual size from each observer were calculated. The results are presented as means Page 3 of 21

4 with standard deviation (SD) and 95% confidence intervals of the mean. For the interand intra-observer repeatability of the measured values and the agreement between the two techniques was assessed using the method described by Bland and Altman. The 95% limit of agreement (LOA) was calculated as the mean difference ± 1.96 SD of the difference. Images for this section: Fig. 1: # Right apex # Middle of the Rt. subpleural lung parenchyme # Rt. upper hilum # Rt. lower hilum # Rt. cardiophrenic angle # Rt. lower retro-hepatic lung parenchyme Page 4 of 21

5 Fig. 2: Fig. 2. TOMO (left) vs CT (right) 3mm nodule in right apex Page 5 of 21

6 Fig. 3: Fig. 3. TOMO (left)vs CT (right) 5mm nodule in right subpleural area Fig. 4: Fig. 4. TOMO (left ) vs CT (right) 5mm nodue in right retrohepatic area Page 6 of 21

7 Fig. 5: Fig. 5. TOMO (left) vs CT (right) 10mm nodule in right lower hilum Page 7 of 21

8 Results Upon initial measurement, one observer judged two of the 3-mm nodules as nonmeasurable on the TOMO modality. One observer judged three of the 3-mm nodules as non-measurable on the CT modality, while another observer judged one of these nodules as non-measurable on CT. Upon their second evaluation, one observer judged two of the 3-mm nodules on TOMO and one 3-mm nodule on CT as non-measurable. The number of measured phantom nodules and mean relative errors for CT and TOMO measurements for each observer are given in Table 1. Table 1. Number of detectednodules, mean relative error and SD for each observer regarding measurements on TOMO images and CT images TOMO images Observer 1 Observer 2 Observer 3 Observer 4 N detected Mean measurement error (mm) SD (mm) CT images N detected Mean measurement error (mm) SD (mm) The mean measurement error for all nodules and all observers was mm (SD: 0.60 CI-0.96/-0.72mm) on TOMO and mm (SD: 0.71, CI -0.33/-0.04 mm) on CT images. The absolute measurement errors for each observer and each nodule on TOMO and CT images are given in Fig.6. On average, all manual measurements on both chest TOMO and CT images underestimated the nodulesize, with the exception of one observer using CT. Fig.7 shows the manual measurement data from TOMO images for the diameters of all nodules and observers plotted against the manual measurement data from CT images. Page 8 of 21

9 The mean measurement errors for the different observers ranged from to mm for TOMO and from to 0.08 for CT. The mean measurement errors with LOA for each observer and size are provided in Table 2. Table 2. Mean measurement error and LOA for real size of the nodules by each observer and size Observer TOMO Mean Lower measurement error LOA (mm) (mm) Upper LOA (mm) CT Mean Lower measurement error LOA (mm) (mm) Upper size LOA (mm) The intra-observer 95% LOA for diameter measurements calculated using the mean of the two measurements as a reference ranged from to 0.50 mm for the least variable observer to to 2.31 mm for the most variable observer using the TOMO modality. For CT measurements, the intra-observer 95% LOA ranged from mm to 0.58 mm to mm to 2.45 mm for the least and most variable observer, respectively. The intraobserver 95% LOA for all observers and each imaging type are provided in Table 3. The inter-observer 95% LOA concerning diameter estimates for each possible pair of radiologists ranged from to 0.83 mm for the least variable pair of radiologists to to 2.36 mm for the most variable pair of radiologists using the TOMO modality. For measurements using the CT modality, the inter-observer 95% LOA ranged from to 0.22 mm to to 2.19 mm for the least and most variable observer pairs, respectively. The inter-observer 95% LOA for all observers and each image type is provided in Table 3. Table 3. Intraobserver and interobserver mean measurement error by observer Page 9 of 21

10 TOMO Intraobserver Mean Lower measurement error LOA (mm) (mm) Upper LOA (mm) CT Mean Lower measurement error LOA (mm) (mm) Upper Interobserver 1 and and and and and and LOA (mm) Assessing the agreement between nodule size measurements of using TOMO and CT by the difference between observers' mean diameter measurement for the two modalities resulted in mean measurement errors of mm (95% confidence interval: -0.91, -0.40) with 95% LOA of to 1.22 mm for comparison of TOMO to CT.Bland-Altman plots illustrating the agreement are provided in Fig.8. The 95% LOA of diameter measurements for individual observers using TOMO and CT images ranged from to 0.37 mm for the least variable observer, to to 2.04 mm for the most variable observer. The 95% LOA for all observers and sizes regarding measurement of the nodule diameter on TOMO and CT are provided in Table 4. Table 4. Mean measurement error at TOMO in comparison to CT by observer and size Observer TOMO compared with CT Mean measurement error (mm) Lower LOA (mm) Upper LOA (mm) Page 10 of 21

11 Size (mm) Bland-Altman plots of the agreement between measurements on TOMO and CT images for the most- and least- experienced radiologists (Fig. 9). Images for this section: Page 11 of 21

12 Fig. 1: # Right apex # Middle of the Rt. subpleural lung parenchyme # Rt. upper hilum # Rt. lower hilum # Rt. cardiophrenic angle # Rt. lower retro-hepatic lung parenchyme Page 12 of 21

13 Fig. 6: Fig. 6 Measurement error for each observer and each nodule on TOMO (left) and CT (right) images compared with the known diameter of the nodule. Dashed line (center) represents the mean measurement error for all nodules and all observers. Dotted lines (top and bottom) represent the mean measurement error #2SD. Page 13 of 21

14 Fig. 7: Fig. 7. Manual measurement data from TOMO images for the diameters of all nodules and observers plotted against manual measurement data from CT images. In plots, the 45 line of equality is drawn to help assess agreement between the measurements. Page 14 of 21

15 Fig. 8: Fig. 8. Bland-Altman plot illustrating the agreement between two modalities. Dashed line (center) = mean difference (-0.65mm [95% confidence interval: -0.91, -0.40]). Dotted lines (top and bottom) = upper and lower limits of agreement. Page 15 of 21

16 Fig. 9: Fig. 9. Plots shows the difference between the nodule diameter measurement on TOMO and CT against the average of the measurements. Graphs show for the most experienced radiologist (left) and least experienced radiologist (right). Page 16 of 21

17 Conclusion In the present study, we evaluated TOMO-derived parameters including nodule diameter; the repeatability of TOMO observations; and the extent of agreement between TOMO data and those afforded by CT. A recent study found that the repeatability values of manual measurements made by TOMO and CT were comparable [7]. In the cited study, clinical nodules that were considered to be adequately segmented were investigated. However, missed nodules on simple radiography are usually at the apices, lung bases, or in central locations adjacent to vessels. It is difficult to perform adequate segmentation of such nodules [8]. Several TOMO phantom studies reported limited underestimation of the true diameter, whereas CT under-or over-estimated nodule size [7, 9-10]. In the present study, both modalities underestimated the diameters of phantom nodules. TOMO appeared to slightly underestimate nodule size (mean measurement error, -0.84mm); however, such an error is clinically relevant, because nodule management is based on an absolute nodule size threshold. In addition, we found that CT also slightly underestimated nodule size (mean measurement error, -0.18mm). The extent of nodule size underestimation by TOMO was somewhat more marked than that affected nodule delineation [11-12]. Such artifacts were mostly investigated in TOMO images for breasts [13-14]. Although we measured nodule diameters from left-to-right (thus not in the direction of the scan), darker areas created a halo around the nodule. This halo was not included in manual measurements of nodule diameter, which affected the results. A more relevant issue is the possible effect of in-plane artifacts on clinical images. Recently, underestimation of nodule size associated with manual measurement of clinical nodules on TOMO has been reported [7]. Svahn et al. found that the extent of in-plane artifacts varied linearly with the spherical diameter and the relative contrast of nodules [15]. Our finding that the tendency toward size underestimation on TOMO images increased as the nodule diameter rose seem to be consistent with their result. The contrast afforded by the 40 acquisition angle of our TOMO images may be greater than that of the images of Johnsson et al in 2010 [16] who used an acquisition angle of 30. This may aggravate in-plane artifacts and underestimation of the sizes of larger nodules since TOMO image contrast increases as the acquisition angle rises. Despite these limitations of TOMO, our present phantom study suggested that the measurement values on CT and TOMO were comparable; the mean difference was -0.65mm. Even with larger nodules (# 5 mm in diameter), the mean difference was less than -1.1mm. Page 17 of 21

18 With regard to repeatability, the inter-observer 95% LOA for measurement of TOMO diameters by the pair of radiologists who recorded most similarly was -0.06~0.83 mm, thus similar to the CT data. These figures were slightly less than the -1.3~1.5 mm variation in measurement of clinical nodules reported by Johnnson et al in 2012 [7]. The intra-observer agreement was of similar magnitude. It is possible that the even shape of phantom nodules was associated with less variation in measurements than was true of clinical nodules. We found that TOMO data including measurement errors, intra- and inter-observer agreement levels, and LOAs, improved in proportion to years of experience. This is also true of CT measurements. Our study had several limitations. As one major drawback in measurement study in phantom nodule is that the observers could guess the true sizes of the studied objects during the two times observation resulting increased repeatability, thus we sought to make observers completely unaware of nodule size and location by presenting random images taken using either imaging modality. Also, the intrinsic limitation of TOMO discussed above has affected our results. Optimization of the TOMO technique, including the plane and angle of acquisition, and construction of the phantom nodule, requires further work. A clinical nodule may vary in shape. Thus, a limitation of TOMO is that size can be estimated in only a single plane, whereas MDCT is three-dimensional. However, the thoracic coronal projection of TOMO is larger than the routine axial image afforded by CT, therefore, it is possible to measure superior-to-inferior nodule diameter on TOMO images more rapidly than is possible using CT data. Moreover, the entire thorax is presented by TOMO with less radiation and shorter study timethan CT. Therefore, TOMO is thought to be taken into account in the nodule detection and follow up for cases with young patients (especially young woman with a risk of breast cancer) and probable benign lesion In conclusion, our results suggest that nodule sizes obtained using TOMO and chest CT are comparable even for thenodules located in areas where size measurement is limited on simple radiograph, because the size difference was less than 1mm, the LOAs of similar width, and the repeatability values similar. However, measurements made by TOMO tended to be smaller than those by CT, and the fact that this tendency was amplified as nodule diameter increased may be of concern if TOMO and CT are to be used interchangeably during nodule follow-up. These concerns may be alleviated in the near future by upgrading TOMO to reduce the number of artifacts encountered in clinical practice. Personal information Page 18 of 21

19 Department of Radiology, Mokdong Hospital, Ewha Womans University School of Medicine, Seoul , Korea; Yookyung Kim, M.D. Department of Radiology, Mokdong Hospital, Ewha Womans University School of Medicine, Seoul, Korea Yu-Whan Oh, M.D. Department of Radiology, Anam Hospital, Korea University, Seoul, Korea; Ki Yeol Lee, M.D. Department of Radiology, Ansan Hospital, Korea University, Seoul, Korea Yon Ju Ryu, M.D. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Mokdong Hospital, Ewha Womans University School of Medicine, Seoul, Korea Myungjae Lee, M. D. Department of Radiology, Mokdong Hospital, Ewha Womans University School of Medicine, Seoul, Korea; References 1. Brogdon BG, Kelsey CA, Moseley RD, Jr. Factors affecting perception of pulmonary lesions. Radiol Clin North Am 1983;21: Shah PK, Austin JH, White CS, et al. Missed non-small cell lung cancer: radiographic findings of potentially resectable lesions evident only in retrospect. Radiology 2003;226: Page 19 of 21

20 3. Gomi T, Nakajima M, Fujiwara H, et al. Comparison between chest digital tomosynthesis and CT as a screening method to detect artificial pulmonary nodules: a phantom study. Br J Radiol 2012;85:e Svalkvist A, Johnsson AA, Vikgren J, et al. Evaluation of an improved method of simulating lung nodules in chest tomosynthesis. Acta Radiol 2012;53: Dobbins JT, McAdams HP, Song JW, et al. Digital tomosynthesis of the chest for lung nodule detection: Interim sensitivity results from an ongoing NIH-sponsored trial. Medical Physics 2008;35: Vikgren J, Zachrisson S, Svalkvist A, et al. Comparison of chest tomosynthesis and chest radiography for detection of pulmonary nodules: human observer study of clinical cases. Radiology 2008;249: Johnsson AA, Fagman E, Vikgren J, et al. Pulmonary nodule size evaluation with chest tomosynthesis. Radiology 2012;265: Girvin F, Ko JP. Pulmonary nodules: detection, assessment, and CAD. AJR American journal of roentgenology 2008;191: Willemink MJ, Leiner T, Budde RP, et al. Systematic error in lung nodule volumetry: effect of iterative reconstruction versus filtered back projection at different CT parameters. AJR Am J Roentgenol 2012;199: Revel MP, Bissery A, Bienvenu M, Aycard L, Lefort C, Frija G. Are twodimensional CT measurements of small noncalcified pulmonary nodules reliable? Radiology 2004;231: Tingberg A, Zackrisson S. Digital mammography and tomosynthesis for breast cancer diagnosis. Expert opinion on medical diagnostics 2011;5: Hu YH, Zhao B, Zhao W. Image artifacts in digital breast tomosynthesis: investigation of the effects of system geometry and reconstruction parameters using a linear system approach. Medical physics 2008;35: Svahn T, Ruschin M, Hemdal B, et al. Inplane artifacts in breast tomosynthesis quantified with a novel contrast-detail phantom. Proc SPIE 2007;6510:65104R 14. Tucker AW, Lu J, Zhou O. Dependency of image quality on system configuration parameters in a stationary digital breast tomosynthesis system. Med Phys 2013;40: Svahn T, Hemdal B, Ruschin M, et al. Dose reduction and its influence on diagnostic accuracy and radiation risk in digital mammography: an observer performance study using an anthropomorphic breast phantom. Brit J Radiol 2007;80: Page 20 of 21

21 16. Johnsson AA, Svalkvist A, Vikgren J, et al. A phantom study of nodule size evaluation with chest tomosynthesis and computed tomography. Radiat Prot Dosimetry 2010;139: Page 21 of 21