Date Published: July 3, 2017
Publisher: Public Library of Science
Author(s): Timothy J. P. Bray, Saurabh Singh, Arash Latifoltojar, Kannan Rajesparan, Farzana Rahman, Priya Narayanan, Sahar Naaseri, Andre Lopes, Alan Bainbridge, Shonit Punwani, Margaret A. Hall-Craggs, Quan Jiang.
To determine which of four Dixon image types [in-phase (IP), out-of-phase (OP), fat only (FO) and water-only (WO)] is most sensitive for detecting multiple myeloma (MM) focal lesions on whole body MRI (WB-MRI) images.
Thirty patients with clinically-suspected MM underwent WB-MRI at 3 Tesla. Unenhanced IP, OP, FO and WO Dixon images were generated and read by four radiologists. On each image type, each radiologist identified and labelled all visible myeloma lesions in the bony pelvis. Each identified lesion was compared with a reference standard consisting of pre- and post-contrast Dixon and diffusion weighted imaging (read by a further consultant radiologist) to determine whether the lesion was truly positive. Lesion count, true positives, sensitivity, and positive predictive value were compared across the four Dixon image types.
Lesion count, true positives, sensitivity and confidence scores were all significantly higher on FO images than on IP images (p>0.05).
FO images are more sensitive than other Dixon image types for MM focal lesions, and should be preferentially read by radiologists to improve diagnostic accuracy and reporting efficiency.
In recent years, whole body-MRI (WB-MRI) has emerged as a valuable tool for assessing disease activity in multiple myeloma (MM).[1–5] MRI is a key component of the Durie-Salmon PLUS staging system, and the number of lesions identified on MRI correlates closely with mortality. As a result, WB-MRI is developing into a first-line imaging modality in MM.[8,9]
Four radiologists read four image series for each of 30 patients (120 image series per radiologist), and identified 610, 955, 549 and 734 lesions respectively compared to 1560 reference lesions. An example of a focal lesion, as shown on the four Dixon image types, is given in Fig 2. A summary of the mean lesion count, true positives, sensitivity, positive predictive value and confidence score for each of the four image types is given in Table 3; these values are also shown graphically in Fig 3. The results of the regression analysis including confidence intervals are also provided in Table 3.
In this study, lesion counts, true positive counts, sensitivity, positive predictive value and reader confidence were compared across the four Dixon images types. We have shown that FO images are superior to other image types and in particular IP images in terms of lesion counts, true positives, sensitivity and confidence. Furthermore, our data suggest that focal lesions demonstrate greater contrast compared to background marrow on FO images than on IP images, which may account for the superior sensitivity of FO images. The positive predictive values for FO images were similar to those for IP and WO images and higher than those for OP images, suggesting that the increase in sensitivity reflects a true increase in lesion conspicuity rather than a lower reader threshold for lesion identification. The use of FO images offered the greatest advantage for patients with focal lesions, but also provided superior sensitivity in patients with diffuse disease.
Fat-only Dixon images offer higher lesion detection rates compared to in-phase images alone in multiple myeloma. We suggest that radiologists should preferentially review the fat-only images when reading to improve diagnostic accuracy and reporting efficiency.