Whole-body MRI in children and adolescents: Can T2-weighted Dixon fat-only images replace standard T1-weighted images in the assessment of bone marrow?

OBJECTIVE: When performing whole-body MRI for bone marrow assessment in children, optimizing scan time is crucial. The aim was to compare T2 Dixon fat-only and TSE T1-weighted sequences in the assessment of bone marrow high signal areas seen on T2 Dixon water-only in healthy children and adolescents. MATERIALS AND METHODS: Whole-body MRIs from 196 healthy children and adolescents aged 6 to 19 years (mean 12.0) were obtained including T2 TSE Dixon and T1 TSE-weighted images. Areas with increased signal on T2 Dixon water-only images were scored using a novel, validated scoring system and classified into "minor" or "major" findings according to size and intensity, where "major" referred to changes easily being misdiagnosed as pathology in a clinical setting. Areas were assessed for low signal on T2 Dixon fat-only images and, after at least three weeks to avoid recall bias, on the T1-weighted sequence by two experienced pediatric radiologists. RESULTS: 1250 high signal areas were evaluated on T2 Dixon water-only images. In 1159/1250 (92.7%) low signal was seen on both T2 Dixon fat-only and T1-weighted sequences while in 24 (1.9%) it was not present on either sequence, with an absolute agreement of 94.6%. Discordant findings were found in 67 areas, of which in 18 (1.5%) low signal was visible on T1-weighted images alone and in 49 (3.9%) on T2 Dixon fat-only alone. The overall kappa value between the two sequences was 0.39. The agreement was higher for major as compared to minor findings (kappa values of 0.69 and 0.29, respectively) and higher for the older age groups. CONCLUSION: T2 Dixon fat-only can replace T1-weighted sequence on whole-body MRI for bone marrow assessment in children over the age of nine, thus reducing scan time.

Whole body magnetic resonance imaging in healthy children and adolescents. Bone marrow appearances of the axial skeleton.

OBJECTIVE: To describe the findings of focal high signal on T2 weighted (T2W) images of the bone marrow in the axial skeleton as assessed by whole-body MRI in healthy and asymptomatic children and adolescents. MATERIAL AND METHODS: We assessed the bone marrow of the mandible, shoulder girdle, thorax, spine, and pelvis on water-only Dixon T2W sequences as part of a whole-body MRI protocol in 196 healthy and asymptomatic children aged 5-19 years. Intensity (0-2 scale) and extension (1-4 scale) of focal high signal areas in the bone marrow were scored and divided into minor or major findings, based on intensity and extension to identify the potentially conspicuous lesions in a clinical setting. RESULTS: We registered 415 areas of increased signal in the axial skeleton whereof 75 (38.3%) were major findings. Fifty-eight (29.6%) individuals had at least one major finding, mainly located in the pelvis (54, 72%). We found no differences according to gender. The number of minor findings increased with age (p = 0.020), but there were no significant differences in the number of major findings. The most conspicuous findings were in the pelvis, spine and sternum. CONCLUSION: Non-specific bone marrow T2W hyperintensities in the axial skeleton are frequently detected on whole-body MRI in healthy, asymptomatic children. Awareness of this is important as some findings may resemble clinically silent lesions in children with suspected multifocal skeletal disease.

Whole body magnetic resonance imaging in healthy children and adolescents: Bone marrow appearances of the appendicular skeleton.

OBJECTIVE: To describe the appearances of bone marrow in the appendicular skeleton on fat-suppressed T2-weighted sequences as assessed by whole-body MRI in healthy and asymptomatic children and adolescents. MATERIAL AND METHODS: Following ethical approval, we assessed the bone marrow of the extremities on water-only Dixon T2-weighted images as part of a whole-body MRI in 196 healthy and asymptomatic children aged 5-19 years. Based on a newly devised and validated scoring system, we graded intensity (0-2 scale) and extension (1-4 scale) of focal high signal bone marrow areas, and divided them into minor or major findings, based on intensity and extension, reflecting their potential conspicuousness in a clinical setting. RESULTS: In the upper extremity, we registered 366 areas with increased signal whereof 79 were major findings. In the lower extremities there were 675 areas of increased signal of which 340 were major findings. Hundred-and-fifteen (58.79%) individuals had at least one major finding, mainly located in the hand and proximal humerus, and the feet and knees. We found no differences according to gender, reported hours of sports activity, handedness, or age group, except for more minor findings in the upper extremities amongst 15-18-year-olds as compared to those aged 5-8 years. CONCLUSION: Focal areas of high signal intensity on whole-body MRI, T2-weighted fat suppressed images that, in a clinical setting could cause concern, were seen in more than half of healthy, asymptomatic children and adolescents. Awareness of this is important when interpreting whole-body MRI in this age group, particularly in the assessment of clinically silent lesions.

Automated segmentation of magnetic resonance bone marrow signal: a feasibility study.

BACKGROUND: Manual assessment of bone marrow signal is time-consuming and requires meticulous standardisation to secure adequate precision of findings. OBJECTIVE: We examined the feasibility of using deep learning for automated segmentation of bone marrow signal in children and adolescents. MATERIALS AND METHODS: We selected knee images from 95 whole-body MRI examinations of healthy individuals and of children with chronic non-bacterial osteomyelitis, ages 6-18 years, in a longitudinal prospective multi-centre study cohort. Bone marrow signal on T2-weighted Dixon water-only images was divided into three color-coded intensity-levels: 1 = slightly increased; 2 = mildly increased; 3 = moderately to highly increased, up to fluid-like signal. We trained a convolutional neural network on 85 examinations to perform bone marrow segmentation. Four readers manually segmented a test set of 10 examinations and calculated ground truth using simultaneous truth and performance level estimation (STAPLE). We evaluated model and rater performance through Dice similarity coefficient and in consensus. RESULTS: Consensus score of model performance showed acceptable results for all but one examination. Model performance and reader agreement had highest scores for level-1 signal (median Dice 0.68) and lowest scores for level-3 signal (median Dice 0.40), particularly in examinations where this signal was sparse. CONCLUSION: It is feasible to develop a deep-learning-based model for automated segmentation of bone marrow signal in children and adolescents. Our model performed poorest for the highest signal intensity in examinations where this signal was sparse. Further improvement requires training on larger and more balanced datasets and validation against ground truth, which should be established by radiologists from several institutions in consensus.

Joint Fluid, Bone Marrow Edemalike Changes, and Ganglion Cysts in the Pediatric Wrist: Features That May Mimic Pathologic Abnormalities-Follow-Up of a Healthy Cohort.

OBJECTIVE: The presence of findings at wrist MRI that may mimic disease is a diagnostic problem. The purpose of this study is to examine the occurrence of bone marrow changes resembling edema, joint fluid, and ganglion cysts over time, in a cohort of healthy children. MATERIALS AND METHODS: Seventy-four of 89 healthy children included in a study of normal MRI findings of the wrists were reexamined after a period of 4 years, using the same 1.5-T MRI technique-namely, a coronal T1-weighted and a T2-weighted fat-saturated sequence. A history of handedness, diseases, and sports activity was noted. RESULTS: Bone marrow edema or edemalike changes were seen in 29 of 74 (39.2%) wrists in 2013 as compared with 35 of 72 (48.6%) wrists in 2009 (p = 0.153), all in different locations. Changes were found in central parts of the bone, on both sides of a joint, or near bony depressions. Fifty percent of all subjects had at least one fluid pocket greater than or equal to 2 mm. The location was unchanged in 47% of the joints. In 24% of the individuals, at least one ganglion cyst was seen. Six ganglion cysts present on the first scan were not seen on the follow-up scan, and 11 new ganglion cysts had appeared. CONCLUSION: Awareness of normal MRI appearances of the growing skeleton is crucial when interpreting MRI of children, and such findings must not be interpreted as pathologic abnormalities.

The many shades of enhancement: timing of post-gadolinium images strongly influences the scoring of juvenile idiopathic arthritis wrist involvement on MRI.

BACKGROUND: Potential long-term side effects of treatment for juvenile idiopathic arthritis are concerning. This has necessitated accurate tools, such as MRI, to monitor treatment response and allow for personalized therapy. OBJECTIVE: To examine the extent to which timing of post-contrast MR images influences the scoring of inflammatory change in the wrist in children with juvenile idiopathic arthritis. MATERIALS AND METHODS: We studied two sets of post-contrast 3-D gradient echo MRI series of the wrist in 34 children with juvenile idiopathic arthritis. These images were obtained immediately after administration of intravenous contrast material and again after approximately 10 min. The dataset was drawn from a prospective multicenter project conducted 2006-2010. We assessed five wrist locations for synovial enhancement, effusion and overall inflammation. Examinations were scored by one radiologist in two sessions - the first was based on the early post-contrast images, and the later session, for which the previous findings were masked, was based on the later post-contrast images. RESULTS: Fifty-two of the 170 locations (30.6%) received a higher synovial enhancement score based on the late post-contrast images as compared to the early images. Sixty of the 170 (35%) locations received a higher total inflammation score. The mean scores of synovial enhancement and total inflammation were significantly higher when based on the late post-contrast images as compared to the early post-contrast images. CONCLUSION: An MRI-based scoring system for the presence and degree of synovitis should be based on a standardized MR-protocol with a fixed interval between intravenous contrast injection and post-contrast images.

Erosion or normal variant? 4-year MRI follow-up of the wrists in healthy children.

BACKGROUND: A large proportion of healthy children have wrist changes on MRI, namely carpal depressions, findings that have been described as pathological in children with juvenile idiopathic arthritis. OBJECTIVE: We performed follow-up imaging in a cohort of healthy children to evaluate carpal surface depressions over time, focusing on the presence of overlying cartilage as a potential discriminator between normal variants and true erosions. MATERIALS AND METHODS: 74 of the initial cohort of 89 healthy children (83%) had a re-scan of their wrists using the same protocol, including coronal T1 and fat-saturated T2 sequences. A cartilage-selective sequence was added for this study. We registered number and location of bony depressions and presence of overlying cartilage. RESULTS: The total number of carpal depressions increased by age group and over time; their location was unchanged in 370 of 487 (76%) carpal sites and 91 of 117 (78%) metacarpal sites. In total, 426 of the 1,087 (39.2%) bony depressions were covered by cartilage, with a decreasing percentage by age (P = 0.001). CONCLUSION: Normal appearances during growth, such as bony depressions, should not be mistaken for pathology. There must be additional findings to support a diagnosis of disease. A cartilage sequence may add to the diagnostic image analysis.