Detection of occult vertebral fractures by quantitative assessment of bone marrow attenuation values at MDCT

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1 Detection of occult vertebral fractures by quantitative assessment of bone marrow attenuation values at MDCT Poster No.: C-1582 Congress: ECR 2014 Type: Scientific Exhibit Authors: F. O. Henes, M. Groth, C. Schaefer, M. Regier, T. Derlin, G. Adam, P. Bannas; Hamburg/DE Keywords: DOI: Musculoskeletal bone, Musculoskeletal spine, CT, MR, Comparative studies /ecr2014/C-1582 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 15

2 Aims and objectives Multidetector computed Tomographie (MDCT): regarded as the first imaging technique of choice for the evaluation of vertebral fractures after trauma 1-2 # Diagnostic limitations 3-5 : Non displaced insufficiency fractures Differentiation between fresh and older fracture components Magnetic Resonance Imaging (MRI): - Higher diagnostic accuracy compared to MDCT High sensitivity for detection of bone marrow oedema (BME) 6-7 Aim of the study: to evaluate the bone marrow with objective comparative Region of Interest (ROI) - based Hounsfield attenuation units (HU) measurements to determine a HU cut-off value for valid and reliable detection of bone marrow oedema related to occult vertebral fractures. Methods and materials Study Population Retrospective study 36 consecutive patients (19#, 17#; mean age: 72,4 years) with backpain after spinal trauma In all patients additional MRI was performed after MDCT imaging to rule out occult vertebral fractures of the thoracolumbar spine during the diagnostic workup Delay between MRI and MDCT with a maximum of 7 days Page 2 of 15

3 In all patients no underlying secondary osseous disease such as metastasis or inflammatory osseous disease were recorded Image analysis: Standard visual image analysis in consensus by two radiologists Analysis in a randomised and blinded fashion Each vertebral body was visually evaluated for the presence or absence of a fresh fracture. Criteria for a acute bone fracture on MDCT were as follows 3,8 : - Presence of a fracture line within the trabecular bone pattern - Disruption in the continuity of the cortex - Sharp step in the cortex - Dislocation of bone fragments Quantitative image analysis: HU measurements in each vertebral body on sagittal images within the trabecular bone independently perfomed by two radiologists Placement of polygonal ROI on two adjacent image slices in the centre of the vertebral body, at the level of the processus spinosus # Calculation of means for further statistical analysis (Fig. 1). Calculation of HU-differences from the vertebral body with the lowest HU value to each other vertebral body in the same patient (Fig. 2). Reference-Standard: Consensus review of MRI examinations by both observers after an interval of 8 weeks. Each of the vertebral bodies was evaluated for the presence or absence of bone marrow oedema and/or fracture lines Page 3 of 15

4 Bone marrow oedema: defined as an area of signal intensity increase on T2-weighted and signal intensity reduction on T1-weighted MR images in the bone marrow pattern (9, 10) Fracture line: defined as a linear structure visualised on either STIR, T1-weighted, or fat-saturated T2-weighted fast spin-echo sequences (9, 10) Statistical analysis I: With MRI serving as the standard of reference, diagnostic accuracy of consensus visual MDCT readings for detection of vertebral fractures was determined by calculation of: # Sensitivity (S) # Specificity (SP) # Positive predictive value (PPV) # Negative predictive value (NPV) Statistical analysis II: Bland-Altman analysis (BAA) and intraclass correlation coefficient (ICC): To assess the agreement of independent quantitative HU measurements of both readers and to demonstrate the bias and limits of agreement of both readings Student's t Test: a) Comparison of absolute attenuation values of affected and unaffected vertebrae as confirmed by MRI b) Comparison of differences of HU values between the vertebra with lowest HU-value and the remaining vertebrae of each patient Receiver operating characteristic (ROC) curve analysis: Page 4 of 15

5 Optimal cut-off derived from ROC curves at the point of highest accuracy was used to calculate the mean S, SP, PPV and NPV Images for this section: Fig. 1 Page 5 of 15

6 Fig. 2 Page 6 of 15

7 Results Overall 202 vertebral bodies were imaged in 36 patients 6 vertebral bodies were excluded from quantitative analysis, one because of vertebral hemangioma, 4 because of vertebral sclerosis due to advanced osteochondrosis and 1 because of total vertebral compression MRI, serving as the standard of reference, revealed bone marrow oedema and trabecular fracture lines in 41 (20.9%) of 196 analysed vertebral bodies in 31 (86.1%) of 36 patients (T11 = 4; T12 = 7; L1 = 8; L2 = 6; L3 = 9; L4 = 5; L5 = 1). Consensual standard visual evaluation of MDCT images: Detection of 32 of 41 fractures (S: 78.0%) Detection of 4 false positive fractures (SP: 97.3%) PPV = 88.9%, PNV = 94.4% Quantitative HU measurements: Bland-Altman analysis revealed a good interobserver agreement with a mean bias of HU (95% limits of agreement, ± 12.6 HU; Fig. 3). HU-measurements in the 41 fractured vertebrae were significantly higher than in the 155 unaffected vertebral bodies (147.1 HU ± 58.5 versus 79.8 ± 46.4 HU, p<0.0001), but with a high variance and a large overlap of HU values between affected and unaffected vertebrae (Fig. 4a). Comparison of the calculated differences of the vertebra with the lowest HU value and the other vertebrae revealed also a significant difference (p<0.0001) between affected (82.5 ± 51.0 HU) and non-affected vertebra (10.7 ± 9.8 HU), but with a reduced variance and overlap of HU values (Fig. 4b). ROC curve analysis revealed a high AUC = (95% confidence interval, ), exhibiting an ideal cut-off value of 29.6 HU density difference for differentiation between the presence and absence of bone marrow edema associated with vertebral fractures (Fig. 5). By using the derived cut-off level of 29.6 HU density difference as evaluation tool for the assessment of bone marrow edema readers achieved an overall higher diagnostic accuracy of 97.4% for fracture detection as compared to visual MDCT evaluation alone (Table 1). Image examples are presented in Figure 6 and 7. Page 7 of 15

8 Table 1 References: Department of Diagnostic and Interventional Radiology, Center for Radiology and Endoscopy, University Medical Center Hamburg-Eppendorf - Hamburg/ DE Images for this section: Page 8 of 15

9 Fig. 3: Interobserver agreement. Bland-Altman plot showing differences between measurements obtained by observer 1 and observer 2. X-axis represents the average of bone marrow density of both observers in Hounsfield units (HU). Y-axis represents the difference between the measurements of observer 1 and observer 2. On each graph, the middle solid line indicates mean bias, and dotted lines above and below indicate 95% confidence intervals. Note the mean bias of only #0.6 HU. Page 9 of 15

10 Fig. 4: Box plot analyses. (a) Box plots of absolute HU values of vertebral bodies with bone marrow oedema (BME+ n = 41) and non-affected vertebra (BME#; n = 155). (b) Calculated CT density differences of the vertebra with the lowest HU value and vertebrae with bone marrow oedema (BME+ n = 41) and non-affected vertebrae (BME#; n = 155), respectively. Both analyses show a significant difference between HU values (p = and p = 0.001, respectively). However, note the higher overlap of absolute HU values (a) and calculated HU value differences between the vertebra with lowest HU and affected and non-affected vertebrae, respectively (b). The difference is due to a significantly reduced variance of calculated differences of unaffected vertebrae (B, BME #) as compared to absolute HU values (A, BME#) of unaffected vertebrae (p < ) Fig. 5: ROC and dot plot analyses. (a) Receiver operating characteristic (ROC) analysis derived from calculated CT density differences of the vertebra with the lowest HU value and vertebrae with bone marrow oedema and non-affected vertebrae, respectively (AUC = 0.978; 95% confidence interval, ). (b) Aligned dot plot analysis of CT density differences (HU) of the vertebra with the lowest HU value and vertebrae with bone marrow oedema and non-affected vertebraeexhibiting an ideal cut-off value of 29.6 HU density difference for differentiation between the presence (BME+) and absence (BME#) of bone marrow oedema. Page 10 of 15

11 Fig. 6: Example 1: Missed occult fracture of L1 in visual CT evaluation correctly identified by quantitative HU measurements in a 89-y-old male patient. MRI demonstrated a hypointense fracture line (arrowhead) in the T1-weighted sequence (a) and a high signal intensity (arrowhead) in T2-weighted image (b) in L1. (c) On visual CT evaluation alone the fracture of L1 (asterisk) was missed. Calculated CT density differences (HU) of the vertebra with the lowest HU value (L4) and L1 revealed a difference of 49.2 HU (asterisk). Hence the presented technique with the use of the cut-off value of 29.6 HU would have detected this occult fracture and was therefore true positive. Numbers indicate absolute HU values, numbers in parentheses indicate CT density differences. Page 11 of 15

12 Fig. 7: Example 2: False-positive rated fracture of L3 in visual CT evaluation correctly ruled out by quantitative HU measurements in a 48-year-old female patient. In MRI neither intravertebral fracture lines in T1-weighted images (a) nor bone marrow oedema in STIRimages (b) were noted. (c) On visual CT evaluation alone the sintered upper endplate of L3 were rated false positively as a fresh vertebral compression fracture (arrow). By chance, the vertebra with lowest HU was L3; hence the calculated difference is 0. In this case the presented technique with the use of the cut-off value of 29.6 HU would have ruled out this false-positively rated fracture by visual CT evaluation and was therefore true-negative. Numbers indicate absolute HU values, numbers in parenthesis indicate CT density differences Page 12 of 15

13 Conclusion Disscussion: Visual MDCT readings failed to detect 9 occult vertebral fractures in 34 patients, which were detected on MRI serving as the standard of reference. This is in line with results of previous studies 6, 7. Our study demonstrates that differences in bone marrow density can be used as a valid tool for the detection of post-traumatic bone marrow oedema associated with vertebral fractures. In correlation with increased amounts of interstitial fluid in the medullary cavity as confirmed by MRI, we observed significantly higher HU values within affected vertebral bodies compared with non-affected levels. Reliable and valid detection of bone marrow oedema was feasible by the establishment of an intraindividual comparative approach. Therefore, for each patient the HU-differences between the vertebra with the lowest HU value and all of the other vertebral bodies were calculated. ROC curve analyses derived the highest diagnostic accuracy with a cut-off value of 29.6 HU difference, particularly by increasing the sensitivity for detection of vertebral fractures occult on visual MDCT readings. Conclusion: Based on the results of our study we recommend the quantitative assessment of bone marrow CT attenuation values in clinical practice as an objective tool during CT reading. This strengthens the decision process and is helpful in deciding whether or not bone marrow oedema is present in the vertebral body after trauma. For the routine use, HU measurements should be simply performed in the centre of all captured vertebral bodies. If differences in means of HU between any of the vertebral bodies are higher than 30 HU than bone marrow oedema due to an occult vertebral fracture in this level is very likely. Limitations: The HU measurement technique cannot detect bone marrow alterations directly adjacent to cortical bone. Degenerative changes that are Page 13 of 15

14 often confined to this area and partial volume effects may falsify HU measurements. Accurate assessment of bone marrow density may be difficult or not possible in some cases including subtotal compression fractures or synchronous vertebral pathology, e.g. benign tumours like hemangioma or suspected malignant underlying disease. Our study population did not include a control group of healthy individuals to assess age- and genderrelated differences in bone marrow density. Personal information References 1. Bagley LJ. Imaging of spinal trauma. Radiol Clin North Am 2006;44:1-12, vii. 2. Parizel PM, van der Zijden T, Gaudino S, et al. Trauma of the spine and spinal cord: imaging strategies. Eur Spine J 2010;19(Suppl ):S Cabarrus MC, Ambekar A, Lu Y, Link TM. MRI and CT of insufficiency fractures of the pelvis and the proximal femur. AJR Am J Roentgenol 2008;191: Henes FO, Groth M, Bley TA, et al. Quantitative assessment of bone marrow attenuation values at MDCT: an objective tool for the detection of bone bruise related to occult sacral insufficiency fractures. Eur Radiol 2012;22(October (10)): Pache G, Krauss B, Strohm P, et al. Dual-energy CT virtual noncalcium technique: detecting posttraumatic bone marrow lesions-feasibility study. Radiology 2010;256(August (2)): Benz BK, Gemery JM, McIntyre JJ, Eskey CJ. Value of immediate preprocedure magnetic resonance imaging in patients scheduled to undergo vertebroplasty or kyphoplasty. Spine (Phila Pa 1976) 2009;34: Spiegl UJ, Beisse R, Hauck S, Grillhosl A, Buhren V. Value of MRI imaging prior to a kyphoplasty for osteoporotic insufficiency fractures. Eur Spine J 2009;18: Page 14 of 15

15 8. Memarsadeghi M, Breitenseher MJ, Schaefer-Prokop C, et al. Occult scaphoid fractures: comparison of multidetector CT and MR imaging-initial experience. Radiology 2006;240: Moulopoulos LA, Yoshimitsu K, Johnston DA, Leeds NE, Libshitz HI. MR prediction of benign and malignant vertebralcompression fractures. J Magn Reson Imaging 1996;6: Jung HS, Jee WH, McCauley TR, Ha KY, Choi KH. Discrimination of metastatic from acute osteoporotic compression spinal fractures with MR imaging. Radiographics 2003;23: Page 15 of 15