Bone marrow lesions in knee osteoarthritis: MR-assessment by manual segmentation and computer-assisted tresholding

Transcription

1 Bone marrow lesions in knee osteoarthritis: MR-assessment by manual segmentation and computer-assisted tresholding Poster No.: P-0073 Congress: ESSR 2012 Type: Scientific Exhibit Authors: F. K. Nielsen, A. G. Jurik, D. Peters, N. Egund; Aarhus/DK DOI: /essr2012/P-0073 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 11

2 Purpose The purposes of the study were to evaluate a manual segmentation method and a computer-assisted thresholding technique for estimating bone marrow lesions (BMLs) in knee osteoarthritis (KOA) over time and compare the results with the most used conventional grading systems. In the commonly used grading methods BMLs are evaluated regarding their approximate size of the total area and in three grades. Thus, in the newly published MOAKS method (1), representing a synthesis of the two most common grading tools, WORMS and BLOKS (2;3), there are three grades of BMLs; grade 1=<33% BML of the total area, grade 2=33-66% and grade 3=>66%.. Methods and Materials A total of 13 patients with medial femorotibial KOA according to the ACR criteria were examined by MRI at baseline and follow-up after 3-12 months. Female/male ratio =12/1; median age 60.5 years ( ). Among several sequences performed using a 1.5 T unit (Vision, Siemens, Erlangen, Germany) with a transmit receive four-channel knee coil, the post-contrast sagittal T1 fat-suppressed (T1FS) sequence was analyzed. The technical sequence parameters were: TR/TE = 860/20 ms, FOV = 16 cm, slice thickness/ interslice gap = 4.0/0.8 mm, matrix 256 x 256, one excitation, TA The dose of Gadolinium (Gd-DTPA 0.2 mmol/ml) was standardized to 0.1 mmol/kg. BMLs were defined as ill-delineated areas of increased signal intensity (SI) on the postcontrast T1FS images. Volumes (mm 3 ) of BMLs in the medial weight-bearing femoral and tibial condyle (52 observations) were measured/calculated on anonymized images by two observers. The manual segmentation (MS) was performed using Agfa Impax software and 2K Bracho screens. The computer assisted tresholding (CAT) method was performed using agraphical user interface for drawing regions of interest (ROIs) and thresholding images written in MATLAB (the MathWorks, Sweden) by D.P. at the Medico-technical Department, Aarhus University Hospital. The areas/volumes of interest of the femoral condyles were separated from the trochlea area/volume as suggested in BLOKS/MOAKS (Fig. 1-3). The area/volume of the tibia included the proximal 2 cm's of the tibial condyles (MS only). By both methods the mean SI (gray scale value, GY) plus one standard deviation (STD) of the normal bone marrow Page 2 of 11

3 of the lateral femoral condyle was used as a relative reference (Figs. 1A and 2). Areas/ volumes with contiguous pixels above this gray scale threshold were considered bone marrow lesions. The total volume of BML was obtained by multiplying the BML areas in each section with the section thickness including the intersection gap. By the manual segmentation, the margins of the areas of BML in each section were constructed by a curved line joining the pixels with threshold values. The correct position of the borderline were controlled by a 5 mm 2 ROI (Figs. 1B, 6) and the margins were adjusted if necessary. The computer calculated BML area was based on counting (with visual coloring) the number of pixels above the threshold in the ROI (Figs. 3, 4). Small clusters of pixels <5 and areas <3 mm 2 were not registered by the CAT and manual method, respectively. The MS and CAT method were tested regarding inter-observer reliability. The results of MS and CAT estimation of BMLs were compared and related to a MOAKS grading of BML. Images for this section: Fig. 1: Manual segmentation. Post-contrast fat suppressed T1-weighted sagittal MR images of the left knee in a 61-year-old female with medial femoro-tibial osteoarthritis. The condylar and trochlear area were separated and constructed according to BLOKS/ modified MOAKS. The reference signal intensity (SI) of normal bone marrow was obtained on a MR section of the lateral femoral condyle (A). The reference area was Page 3 of 11

4 682 mm2, mean SI = 330 GY (gray scale value) with STD = 31. The relative reference SI used was 361 GY (330+31). (B) MR section of the medial femoral condyle with contrast enhancement of bone marrow lesions. The manually segmented area with GY > 361(relative reference GY) was 325 mm2, mean SI = 541 GY. The SI of two 5 mm2 test areas was 342 GY (arrow) and 380 GY (arrowhead), respectively. Fig. 2: Computer assisted thresholding (Figures 2 and 3, A and B) of bone marrow lesions in the same patient and MR sections as in Figure 1. (A) The area of interest of the normal bone marrow of the lateral femoral condyle was 546 mm2. The vertical red line in the histogram shows a threshold value of GY (mean SI GY plus one STD = 28.05) which was used in the medial compartment (B, Figure 3). (B, Figure 3) The total area of interest of the medial femoral condyle was 767 mm2. The number of pixels above threshold (red) was 3924 = 55% of the total area or mm2. The thresholded pixels on the histogram had a mean of 433 GY. Page 4 of 11

5 Fig. 3: Computer assisted thresholding (Figures 2 and 3, A and B) of bone marrow lesions in the same patient and MR sections as in Figure 1. (A) The area of interest of the normal bone marrow of the lateral femoral condyle was 546 mm2. The vertical red line in the histogram shows a threshold value of GY (mean SI GY plus one STD = 28.05) which was used in the medial compartment (B, Figure 3). (B, Figure 3) The total area of interest of the medial femoral condyle was 767 mm2. The number of pixels above threshold (red) was 3924 = 55% of the total area or mm2. The thresholded pixels on the histogram had a mean of 433 GY. Page 5 of 11

6 Fig. 4: Artifact recognition (Figures 4-6) by manual segmentation and computer assisted thresholding (CAT) of bone marrow lesions. Same patient and left knee as in Figures 1-3. (A, Figure 4) The CAT of the MR section lateral to the section in Figure 1B and Figure 3 shows an area with extensive number of pixels above the threshold (red). (B, Figure 5) The second next lateral section included enhancing soft tissue of the intercondylar region influencing the pixel values by CAT. (C, Figure 6) The same section as in Figure 4 (A). The area/volume D (arrow) with partial volume artifacts can manually be excluded from the total volume of bone marrow lesions. Page 6 of 11

7 Fig. 5: Artifact recognition (Figures 4-6) by manual segmentation and computer assisted thresholding (CAT) of bone marrow lesions. Same patient and left knee as in Figures 1-3. (A, Figure 4) The CAT of the MR section lateral to the section in Figure 1B and Figure 3 shows an area with extensive number of pixels above the threshold (red). (B, Figure 5) The second next lateral section included enhancing soft tissue of the intercondylar region influencing the pixel values by CAT. (C, Figure 6) The same section as in Figure 4 (A). The area/volume D (arrow) with partial volume artifacts can manually be excluded from the total volume of bone marrow lesions. Page 7 of 11

8 Fig. 6: Artifact recognition (Figures 4-6) by manual segmentation and computer assisted thresholding (CAT) of bone marrow lesions. Same patient and left knee as in Figures 1-3. (A, Figure 4) The CAT of the MR section lateral to the section in Figure 1B and Figure 3 shows an area with extensive number of pixels above the threshold (red). (B, Figure 5) The second next lateral section included enhancing soft tissue of the intercondylar region influencing the pixel values by CAT. (C, Figure 6) The same section as in Figure 4 (A). The area/volume D (arrow) with partial volume artifacts can manually be excluded from the total volume of bone marrow lesions. Page 8 of 11

9 Results The inter-observer agreement for BML volumes by MS was good, linear weighted kappa value 0.88 (CI ) with no difference regarding femoral and tibial volumes (kappa 0.85), respectively. Based on 24 estimations the inter-observer agreement for BML volume bycat was also good, linear weighted kappa values 0.84 (CI ). The CAT methodfailed in two examinations due to apparently uneven contrastenhancement with varying signal intensity of normal bone across the knee. A consensus was made regarding these examinations by drawing the ROI in close proximity to observed BML and avoiding areas of unwanted signal variation (Figs. 4-6). The consensus results were used in the comparison with the MS results. The BML values obtained by MS and CAT, respectively, were significantly correlated (#=0.94 (CI )) and the median values were similar. MOAKSgrade/percentage BML of the total femoral or tibial condyle volume were 1/<33%: n=19; 2/33-66%: n=4; 3/>66%: n=3. Detected BML changes in volumes during follow-up were: <4%: n=15; <33%: n= 9; 33-66%: n=0; >66%: n=2. Thus, the change over time was only detectable in two knees by MOAKS. Conclusion MS and CAT can estimate BML changes over time not detectable by MOAKS. The CAT method should, however, be used with caution. The presented manual segmentation grading method, though time consuming, can be used without dedicated computer software. It was found to be sensitive to detecting even minor changes in BML volume making it advantageous specifically given the fluctuating nature of BML (4). Thresholding is a popular technique in image segmentation (5;6)in which a number of pixels are selected based on pixel intensity. The results can be obtained fast and theuse of computerized thresholding therefore seems encouraging but should be used with caution. In two of the present examinations the CAT method failed due to the signal intensity of normal bone varying from the outside toward the inside of the knee. The source of error is most likely due to partial volume artifact, poor positioning of the knee inside the receiving coil, B1 inhomogeneity or poor shimming. This has not been fully Page 9 of 11

10 explored. Furthermore, CAT does not differentiate between pathological or physiological entities, including e.g. blood vessels, resulting in a potential overestimation of the BML volume. Due to large and ill-defined transitions of BMLs in KOA, precise area/volume measurements remain a challenge. Additional grading of SI and/or dynamic contrast MR imaging may add to clarify the clinical significance of BMLs in OA. References 1: Hunter DJ, Guermazi A, Lo GH, Grainger AJ, Conaghan PG, Boudreau RM, Roemer FW: Evolution of semi-quantitative whole joint assessment of knee OA: MOAKS (MRI Osteoarthritis Knee Score). Osteoarthritis Cartilage 2011, 19(8): : Peterfy CG, Guermazi A, Zaim S, Tirman PF, Miaux Y, White D, Kothari M, Lu Y, Fye K, Zhao S, Genant HK:Whole-Organ Magnetic Resonance Imaging Score (WORMS) of the knee in osteoarthritis. Osteoarthritis Cartilage 2004, 12(3): : Hunter DJ, Lo GH, Gale D, Grainger AJ, Guermazi A, Conaghan PG: The reliability of a new scoring system for knee osteoarthritis MRI and the validity of bone marrow lesion assessment: BLOKS (Boston Leeds Osteoarthritis Knee Score). Ann Rheum Dis 2008, 67(2): : Kornaat PR, Kloppenburg M, Sharma R, Botha-Scheepers SA, Le Graverand MP, Coene LN, Bloem JL, Watt I: Bone marrow edema-like lesions change in volume in the majority of patients with osteoarthritis; associations with clinical features. Eur Radiol 2007, 17(12): : Hunter DJ, Zhang Y, Niu J, Goggins J, Amin S, LaValley MP, Guermazi A, Genant H, Gale D, Felson DT: Increase in bone marrow lesions associated with cartilage loss: A longitudinal magnetic resonance imaging study of knee osteoarthritis. Arthritis Rheum 2006, 54(5): : Roemer FW, Guermazi A, Javaid MK, Lynch JA, Niu J, Zhang Y, Felson DT, Lewis CE, Torner J, Nevitt MC, MOST Study investigators: Change in MRI-detected subchondral bone marrow lesions is associated with cartilage loss: the MOST Study. A longitudinal multicentre study of knee osteoarthritis. Ann Rheum Dis 2009, 68(9): Page 10 of 11

11 7: Fotinos-Hoyer AK, Guermazi A, Jara H, Eckstein F, Ozonoff A, Khard H, Norbash A, Bohndorf K, Roemer FW: Assessment of synovitis in the osteoarthritic knee: Comparison between manual segmentation, semiautomated segmentation, and semiquantitative assessment using contrast-enhanced fat-suppressed T1- weighted MRI. Magn Reson Med 2010, 64(2): : Mayerhoefer ME, Breitenseher M, Hofmann S, Aigner N, Meizer R, Siedentop H, Kramer J: Computer-assisted quantitative analysis of bone marrow edema of the knee: initial experience with a new method. AJR.American journal of roentgenology , 182(6): : Mayerhoefer ME, Breitenseher MJ, Kramer J, Aigner N, Norden C, Hofmann S: STIR vs. T1-weighted fat-suppressed gadolinium-enhanced MRI of bone marrow edema of the knee: computer-assisted quantitative comparison and influence of injected contrast media volume and acquisition parameters. J Magn Reson Imaging 2005, 22(6): Personal Information Page 11 of 11