Diffusion-Weighted Magnetic Resonance Imaging of Spinal Infection and Malignancy

Rapid MRI for acute pediatric MSK infections: survey of current utilization and procedural practices

BACKGROUND

Some institutions have implemented rapid MRI protocols for acute musculoskeletal (MSK) infections as an attempt to improve early diagnosis.

OBJECTIVE

To assess current utilization of pediatric rapid MSK MRI protocols (abbreviated protocol, no IV (intravenous) contrast, and no sedation) using a survey.

MATERIALS AND METHODS

A 10-question survey was sent to members of the Society for Pediatric Radiology (SPR) and the Society of Skeletal Radiology, which differed depending on whether a rapid protocol was used or not. The survey was conducted by the SPR MSK and MRI committees.

RESULTS

A total of 134 surveys (representing 99 institutions) were completed. Twenty-two percent (22/99) of institutions used a rapid protocol. Pediatric institutions were more likely to perform it when compared to adult institutions (P-value<0.01, 37% (14/38) vs. 13% (8/61)). Comparing institutions that use rapid protocol with institutions that do not, the availability of on-call MRI technologists did not differ (P-value=0.33), and pediatric radiologists were more likely to interpret these studies (73% (16/22) vs. 36% (28/77), P-value=0.02). Reported rapid MRI completion times took less than 15 min in 64% (14/22) of the institutions. Seventy-three percent (16/22) of institutions performing rapid protocols have radiologists check images to evaluate the need for additional sequences or contrast. Sixty-eight percent (25/37) reported being very satisfied with rapid protocols. Seventy-seven of 99 institutions do not use a rapid protocol due to a lack of a consensus protocol and concerns about missing findings. Of these institutions, 62% (48/77) administer IV contrast routinely.

CONCLUSION

There is limited and variable utilization of rapid MRI protocols for acute pediatric MSK infection. Lack of accepted consensus protocol is the most common reason for non-implementation, highlighting the need for consensus-driven rapid protocols.

Echo-planar DWI variants: A comparative study in vertebral marrow pathology

PURPOSE

Single-shot echo-planar imaging (ss-EPI) has limited application in vertebral column imaging due to numerous artifacts. Therefore, we aimed to compare readout-segmented echo-planar imaging (rs-EPI) to ss-EPI and assess its value in the differential diagnosis of vertebral infectious, tumoral infiltrative, and degenerative disorders.

MATERIALS AND METHODS

Sixty-six adult patients with spondylodiscitis (SD, n = 26), tumoral infiltration (TI, n = 20), or Modic type I degeneration (DE, n = 20) findings on spinal magnetic resonance imaging (MRI) included in this retrospective study. Two radiologists scored images for quality on a 4-point scale (image resolution, degree of geometric distortion, lesion selectivity, and diagnostic reliability) and measured signal intensity (SI), apparent diffusion coefficient (ADC), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). DE and SD groups also united to form the benign group.

RESULTS

In all groups, rs-EPI performed better than ss-EPI in image quality, SNR, and CNR (p < 0.05). The difference between mean pathological ADC (ADCP) in the two sequences was statistically significant (p < 0.05). There was no significant difference between the groups in terms of ADCP in rs-EPI (p = 0.229), unlike ss-EPI (p = .025). Pathological SI (SIP) and CNR in rs-EPI were significantly higher in the malignant group than benign group (p = 0.002, p < 0.001). In rs-EPI, no significant difference was found between malignant and benign groups' ADCP (p = 0.13).

CONCLUSION

The rs-EPI is a diffusion-weighted imaging (DWI) method with higher image quality that diminishes motion-induced phase errors and increases resolution through phase corrections. However, the distinction of malignant and benign vertebral bone marrow pathologies is unsatisfactory for rs-EPI compared with ss-EPI.

The advancement of MRI in differentiating Modic type I degenerative changes from early spinal infections

MRI is the most sensitive and specific imaging method for the detection of advanced spinal infections. However, the differential diagnosis of early spinal infection and Modic Type I degenerative changes based on conventional MRI is difficult clinically, as they both may mimic each other by showing hypointensity on T1 weighted images and hyperintensity on T2 weighted spine MRI images. This review summarizes recent advancements in MRI, which may be useful in discriminating degenerative Modic Type I endplate changes from early spinal infection, and evaluates the diagnostic accuracy and limitations of MRI. We aim to provide indications for early differential diagnosis to help initiate appropriate treatment in a timely manner so that associated complications can be avoided.

Incremental value of diffusion weighted imaging over conventional MRI for the diagnosis of osteomyelitis of extremities

OBJECTIVE

To determine the incremental value of diffusion weighted imaging (DWI) over conventional MR imaging in diagnosing extremity osteomyelitis (OM).

MATERIALS AND METHODS

In this cross-sectional study, three experienced musculoskeletal radiologists evaluated clinically suspected cases of extremity OM in two rounds-first on conventional MR imaging, and then conventional MR imaging combined with DWI 4-6 weeks later. The readers recorded a result of the presence or absence of OM and their diagnostic confidence on a 1-5 scale. Mean and minimum apparent diffusion coefficient (ADC) were measured. Pathology diagnosis served as the reference standard. Statistical analysis utilized intraclass correlation (ICC) and Conger's kappa.

RESULTS

A total of 213 scans of suspected OM were reviewed by three musculoskeletal radiologists with no significant changes in sensitivity (0.97, 0.97), specificity (0.97, 0.94), positive predictive value (0.91, 0.87), or negative predictive value (0.98, 0.98) between conventional MR imaging and MR imaging combined with DWI, respectively. Reader confidence did not significantly change with the addition of DWI (4.55 and 4.70, respectively). A high inter-reader agreement was observed for the diagnosis of OM, soft tissue abscess, and intraosseous abscess in both rounds. A higher mean (1.46+/-0.43 × 10-3 mm2/s > 0.64+/-0.47 × 10-3mm2/s) and minimum (1.18+/-0.45 × 10-3mm2/s > 0.37+/-0.44 × 10-3mm2/s) ADC value was associated with OM (p-value < 0.0001) with odds ratios of 1.34 and 1.31, respectively, for mean and minimum ADC of the involved bone.

CONCLUSION

DWI-derived ADC increase is associated with OM. The use of DWI slightly increases reader confidence in the diagnosis of OM; however, no significant incremental value over conventional MR imaging is seen for the final diagnosis of OM.

Advances in Bone Marrow Imaging: Strengths and Limitations from a Clinical Perspective

Conventional magnetic resonance imaging (MRI) remains the modality of choice to image bone marrow. However, the last few decades have witnessed the emergence and development of novel MRI techniques, such as chemical shift imaging, diffusion-weighted imaging, dynamic contrast-enhanced MRI, and whole-body MRI, as well as spectral computed tomography and nuclear medicine techniques. We summarize the technical bases behind these methods, in relation to the common physiologic and pathologic processes involving the bone marrow. We present the strengths and limitations of these imaging methods and consider their added value compared with conventional imaging in assessing non-neoplastic disorders like septic, rheumatologic, traumatic, and metabolic conditions. The potential usefulness of these methods to differentiate between benign and malignant bone marrow lesions is discussed. Finally, we consider the limitations hampering a more widespread use of these techniques in clinical practice.

Diffusion-Weighted Imaging Distinguishes Between Osteomyelitis, Bone Marrow Edema, and Healthy Bone on Forefoot Magnetic Resonance Imaging

BACKGROUND

Diagnosis of osteomyelitis by imaging can be challenging. The feasibility of diffusion-weighted imaging (DWI) as ancillary sequence was evaluated in this study.

PURPOSE

To evaluate DWI for differentiation between osteomyelitis, bone marrow edema, and healthy bone on forefoot magnetic resonance imaging (MRI).

STUDY TYPE

Prospective.

SUBJECTS

A total of 60 consecutive patients undergoing forefoot MRI divided into three study groups (20 subjects each): osteomyelitis, bone marrow edema, and healthy bone.

FIELD STRENGTH/SEQUENCE

A 1.5T and 3T MRI scanners; readout-segmented multishot echo planar DWI.

ASSESSMENT

Two independent radiologists measured apparent diffusion coefficient (ADC) values within abnormal or healthy bone.

STATISTICAL TESTS

ADC values were compared between groups (pairwise t-test with Bonferroni-Holm correction for multiple testing). Intraclass correlation coefficient (ICC) was calculated to assess inter-reader agreement. Threshold ADC values were determined as the cutoffs that maximized the sum of sensitivity and specificity. Receiver operating characteristic (ROC) analysis was performed with statistical threshold of P < 0.05.

RESULTS

Inter-reader agreement was 0.92 in the healthy bone group and 0.78 in both the edema and osteomyelitis groups. Average ADC values were significantly different between groups: 1432 ± 222 × 10^-6  mm² /sec (osteomyelitis), 1071 ± 196 × 10^-6  mm² /sec (bone marrow edema), and 277 ± 89 × 10^-6  mm² /sec (healthy bone). A threshold ADC value of 534 × 10^-6  mm² /sec distinguishes between healthy and abnormal bone with specificity and sensitivity of 100% each. For distinction between osteomyelitis and bone marrow edema, two cutoff values were determined: a 95%-specificity cutoff indicating osteomyelitis (>1320 × 10^-6  mm² /sec) and a 95%-sensitivity cutoff indicating bone marrow edema (<1155 × 10^-6  mm² /sec). Diagnostic accuracy of 95% was achieved for 73% (29/40) of the subjects.

DATA CONCLUSION

DWI with ADC maps distinguishes between healthy and abnormal bone on forefoot MRI. Calculated cutoff values allow confirmation or exclusion of osteomyelitis in a high proportion of subjects.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Magnetic resonance imaging protocols for pediatric acute hematogenous osteomyelitis

Pediatric musculoskeletal infection can be a challenging clinical diagnosis. MRI protocols should be tailored appropriately to diagnose and localize sites of infection, to determine alternative pathologies that could explain the child's presentation, and to identify complications that could alter treatment or lead to devastating consequences in growing bones. In this review, we discuss MRI protocols tailored for suspected acute appendicular musculoskeletal infection in children. These protocols are based on patient age in order to generally reflect the developmental stage of the child, the corresponding relevant anatomy and physiology, and the skeletal maturity-dependent physiopathology of musculoskeletal infections.

Pediatric skeletal diffusion-weighted magnetic resonance imaging, part 2: current and emerging applications

Diffusion-weighted imaging (DWI) complements the more established T1, fluid-sensitive and gadolinium-enhanced magnetic resonance pulse sequences used to assess several pediatric skeletal pathologies. There is optimism that the technique might not just be complementary but could serve as an alternative to gadolinium and radiopharmaceuticals for several indications. As a non-contrast, free-breathing and noninvasive technique, DWI is especially valuable in children and is readily incorporated into existing MRI protocols. The indications for skeletal DWI in children include distinguishing between benign and malignant skeletal processes, initial assessment and treatment response assessment for osseous sarcomas, and assessment of inflammatory arthropathies and femoral head ischemia, among others. A notable challenge of diffusion MRI is the dynamic nature of the growing pediatric skeleton. It is important to consider the child's age when placing DWI findings in context with potential marrow pathology. This review article summarizes the current and evolving applications of DWI for assessing the pediatric skeleton, rounding off the discussion with evolving directions for further research in this realm.

Assessment of diffusion tensor imaging in differentiation between pyogenic and tuberculous spondylitis

PURPOSE

to assess diffusion tensor imaging (DTI); an emerging technique for differentiation between pyogenic and tuberculous spondylitis.

PATIENTS AND METHODS

The study was carried out on 33 patients with infective spondylitis performing conventional MRI and DTI. The mean diffusivity (MD) and fractional anisotropy (FA) of the affected vertebral body were calculated by two readers.

RESULTS

The MD of pyogenic spondylitis of both readers (1.48 ± 0.09 and 1.47 ± 0.08 × 10^-3 mm²/s) were significantly higher values (P = 0.001) than tuberculous spondylitis (1.11 ± 0.15 and 1.18 ± 0.08 × 10^-3 mm²/s). The FA of pyogenic spondylitis of both readers (0.18 ± 0.09 and 0.20 ± 0.08) were significantly lower values (P = 0.001) than tuberculous spondylitis (0.30 ± 0.05 and 0.32 ± 0.03). There was a strong inter-reader agreement between both readers using MD (K = 0.963) and FA (K = 0.858). The thresholds MD and FA used for differentiating pyogenic and tuberculous spondylitis of both readers were 1.37 and 1.33 × 10^-3 mm²/s and 0.21 and 0.25 with the area under the curve (AUC) of 0.927 and 0.831 respectively. Combined MD and FA revealed increased AUC to 0.97 and 0.98 of both readers respectively.

CONCLUSION

DTI with its parameters can be considered a noninvasive beneficial quantitative method that can help in differentiation between pyogenic and tuberculous spondylitis.

Clinical suspicion of spondylodiscitis with equivocal MRI findings: does diffusion-weighted imaging prove helpful here?

BACKGROUND

Despite the high sensitivity of magnetic resonance imaging (MRI), early detection of spondylodiscitis (SpD) remains challenging due to its low specificity.

PURPOSE

To assess the diagnostic value of diffusion-weighted imaging (DWI) in suspected cases of SpD with ambiguous early MRI findings in the differentiation of degenerative disorders (DD).

MATERIAL AND METHODS

In this prospective study, 52 patients suspected of having SpD underwent a whole-spine 3-T MRI scan comprising sagittal DWI. Of 58 conspicuous, T2-weighted, signal increased discs, 39 were successfully evaluated using DWI. Apparent diffusion coefficient (ADC) values and ADC maps were blindly analyzed using the region of interest of the conspicuous disc and a normal adjacent reference disc. Intraindividual ratios (conspicuous disc: reference disc) were calculated.

RESULTS

All conspicuous discs showed increased absolute ADC values, which did not differ significantly between SpD (n = 22) and DD (n = 17). However, ADC ratio was significantly higher in SpD vs. DD (P < 0.05). In receiver operating characteristic curve analysis, an ADC ratio threshold of 1.6 resulted in 45% sensitivity and 88% specificity (area under the curve = 0.69) for SpD diagnosis.

CONCLUSION

The absolute ADC value does not provide a reliable diagnosis of SpD. Increased diffusivity can be an indication of infection but should always be discussed in the context of existing disc degeneration.

Intravoxel incoherent motion MR imaging for differentiating malignant lesions in spine: A pilot study

PURPOSE

To determine the diagnostic potential of Intravoxel Incoherent Motion (IVIM) MRI for differentiating malignant spinal tumours from acute vertebral compression fractures and tuberculous spondylitis, and to compare IVIM with diffusion-weighted imaging (DWI) and chemical shift imaging (CSI).

METHODS

The Institutional Review Board approved this prospective study, and informed consent was obtained. IVIM MRI, DWI, and CSI at 1.5 T were performed in 25 patients with 12 acute compression fractures, 14 tuberculous spondylitis, and 18 malignant spinal tumours. The parameters of these techniques were assessed using the Kruskal-Wallis test. The diagnostic performance of the parameters was evaluated using receiver operating characteristic (ROC) analysis.

RESULTS

ADC, SIR, D_slow, D_fast, and f values of malignant tumours were significantly different from those of acute compression fracture (for all, p < 0.05). The mean D_slow and D_fast values of malignant spinal tumours had significant differences compared with those of tuberculous spondylitis (for all, p < 0.05). However, no significant differences were observed in any quantitative parameters between the acute compression fracture and the tuberculous spondylitis (p > 0.05). D_slow•f showed the highest AUC value of 0.980 (95%CI: 0.942-1.000) in differentiating acute compression fracture and malignant spinal tumours. D_slow showed the highest AUC value of 0.877 (95%CI: 0.713-0.966) in differentiating tuberculous spondylitis and malignant spinal tumours.

CONCLUSIONS

IVIM MR imaging may be helpful for differentiating malignant spinal tumours from acute vertebral compression fractures and tuberculous spondylitis.

Differentiation of breast tuberculosis and breast cancer using diffusion-weighted, T2-weighted and dynamic contrast-enhanced magnetic resonance imaging

Background

The use of multi-parametric magnetic resonance imaging (MRI) in the evaluation of breast tuberculosis (BTB).

Objectives

To evaluate the value of diffusion-weighted imaging (DWI), T2-weighted (T2W) and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in differentiating breast cancer (BCA) from BTB.

Method

We retrospectively studied images of 17 patients with BCA who had undergone pre-operative MRI and 6 patients with pathologically proven BTB who underwent DCE-MRI during January 2014 to January 2015.

Results

All patients were female, with the age range of BTB patients being 23–43 years and the BCA patients being 31–74 years. Breast cancer patients had a statistically significant lower mean apparent diffusion coefficient (ADC) value (1072.10 ± 365.14), compared to the BTB group (1690.77 ± 624.05, p = 0.006). The mean T2-weighted signal intensity (T2SI) was lower for the BCA group (521.56 ± 233.73) than the BTB group (787.74 ± 196.04, p = 0.020). An ADC mean cut-off value of 1558.79 yielded 66% sensitivity and 94% specificity, whilst the T2SI cut-off value of 790.20 yielded 83% sensitivity and 83% specificity for differentiating between BTB and BCA. The homogeneous internal enhancement for focal mass was seen in BCA patients only.

Conclusion

Multi-parametric MRI incorporating the DWI, T2W and DCE-MRI may be a useful tool to differentiate BCA from BTB.

Diffusion imaging of the vertebral bone marrow

Diffusion-weighted MRI (DWI) of the vertebral bone marrow is a clinically important tool for the characterization of bone-marrow pathologies and, in particular, for the differentiation of benign (osteoporotic) and malignant vertebral compression fractures. DWI of the vertebral bone marrow is, however, complicated by some unique MR and tissue properties of vertebral bone marrow. Due to both the spongy microstructure of the trabecular bone and the proximity of the lungs, soft tissue, or large vessels, substantial magnetic susceptibility variations occur, which severely reduce the magnetic field homogeneity as well as the transverse relaxation time T^*₂ , and thus complicate MRI in particular with echoplanar imaging (EPI) techniques. Therefore, alternative diffusion-weighting pulse sequence types such as single-shot fast-spin-echo sequences or segmented EPI techniques became important alternatives for quantitative DWI of the vertebral bone marrow. This review first describes pulse sequence types that are particularly important for DWI of the vertebral bone marrow. Then, data from 24 studies that made diffusion measurements of normal vertebral bone marrow are reviewed; summarizing all results, the apparent diffusion coefficient (ADC) of normal vertebral bone marrow is typically found to be between 0.2 and 0.6 × 10^-3  mm² /s. Finally, DWI of vertebral compression fractures is discussed. Numerous studies demonstrate significantly greater ADCs in osteoporotic fractures (typically between 1.2 and 2.0 × 10^-3  mm² /s) than in malignant fractures or lesions (typically 0.7-1.3 × 10^-3  mm² /s). Alternatively, several studies used the (qualitative) image contrast of diffusion-weighted acquisitions for differentiation of lesion etiology: a very good lesion differentiation can be achieved, particularly with diffusion-weighted steady-state free precession sequences, which depict malignant lesions as hyperintense relative to normal-appearing vertebral bone marrow, in contrast to hypointense or isointense osteoporotic lesions. Copyright © 2015 John Wiley & Sons, Ltd.

Vertebral bone marrow diffusivity in healthy adults at 3T diffusion-weighted imaging

BACKGROUND

There has been controversy surrounding the relationship between diffusivity and age in vertebral bone marrow. In particular, gender-related factors that influence the vertebral bone marrow conditions have not yet been identified.

PURPOSE

To determine the age- and gender-related diffusivity changes of the lumbar bone marrow by measuring the apparent diffusion coefficient (ADC) values.

MATERIAL AND METHODS

A total of 125 healthy adult volunteers were enrolled in this study. Sagittal magnetic resonance (MR) diffusion-weighted imaging (DWI) of the lumbar spine was performed. The ADC values of vertebral bone marrow were measured and compared between gender and age groups. Correlation analysis was used to evaluate the correlation between the ADC values and age.

RESULTS

The ADC values of the female participants were significantly higher than those of the male participants (P = 0.023). Among individuals aged less than 50 years, the ADC values of the female participants were significantly higher than those of the male participants (P < 0.001). The ADC values of the pre-menopausal female participants were significantly higher than post-menopausal female participants (P < 0.001). The ADC value was also significantly and negatively correlated with age (r = -0.334, P = 0.001), particularly among women (r = -0.581, P < 0.001).

CONCLUSION

Bone marrow ADC values of the lumbar spine demonstrated gender- and age-related differences. In particular, gender difference occurred among participants aged less than 50 years. These findings likely reflect changes in the cellular component of the lumbar bone marrow.

Diffusion-weighted magnetic resonance imaging in differentiating acute infectious spondylitis from degenerative Modic type 1 change; the role of b-value, apparent diffusion coefficient, claw sign and amorphous increased signal

OBJECTIVE

To examine the effect of using different b-values on the utility of diffusion-weighted (DW) MRI in differentiating acute infectious spondylitis from Modic type 1 and the discriminative accuracy of related apparent diffusion coefficient (ADC), claw-sign and amorphous increased signal.

METHODS

43 patients with equivocal diagnosis of acute infectious spondylitis/Modic type 1 by using MR images were prospectively studied. The discriminative accuracy of DW MRI using three b-values of 50, 400, 800 s mm(-2), ADC, claw sign and amorphous increased signal was examined.

RESULTS

DW MRI differentiated infectious spondylitis from Modic type 1 change most accurately when a b-value of 800 s mm(-2) was chosen [sensitivity, 91.7%; specificity, 96.8%; positive-predictive value (PPV), 91.7%; negative-predictive value (NPV), 96.8%; and accuracy, 95.3%]. The optimal cut-off ADC value was 1.52 × 10(-3) mm(2) s(-1) (sensitivity, 91.7%; specificity, 100%; PPV, 100%; NPV, 96.9%; and accuracy, 97.7%). Best visualized at a b-value of 50 s mm(-2), claw sign (for degeneration) and amorphous increased signal (for infection) were 100% accurate.

CONCLUSION

Should DW MRI be used in differentiating acute infectious spondylitis from degeneration, large b-values are required. With low b-values, however, claw sign and amorphous increased signal are very accurate in this regard.

ADVANCES IN KNOWLEDGE

DW MRI using large b-values could be used in differentiating acute infectious spondylitis from Modic type I.

Pediatric and adult spinal tuberculosis: imaging and pathophysiology

The prevalence of tuberculosis (TB) has increased in developing and developed countries as a consequence of the AIDS epidemic, immigration, social deprivation, and inadequate TB control and screening programs. Spinal TB may be osseous or nonosseous. Classic findings of multiple contiguous vertebral body involvement, gibbus formation, and subligamentous spread with paravertebral abscesses are optimally evaluated with MR imaging. Nonspondylitic spinal TB is less well described in the literature, may develop in the absence of TB meningitis, and is often associated with meningovascular cord ischemia. Radiologists should be familiar with the spectrum of imaging findings, allowing early diagnosis and treatment of this serious condition.

Infections of the spine and spinal cord

Predisposing factors for developing spinal infections include: immunodeficiency; drug abuse; the widespread use of broad-spectrum antibiotics, corticosteroids, and immunosuppressive drugs; diabetes mellitus; and spinal surgery. Infections can be bacterial, fungal, parasitic, or viral in origin. This chapter reviews current knowledge in clinical and imaging findings in the most common spinal infections divided according to the compartment primarily involved.

Pyogenic and non-pyogenic spinal infections: emphasis on diffusion-weighted imaging for the detection of abscesses and pus collections

The incidence of spinal infections has increased in the past two decades, owing to the increasing number of elderly patients, immunocompromised conditions, spinal surgery and instrumentation, vascular access and intravenous drug use. Conventional MRI is the gold standard for diagnostic imaging; however, there are still a significant number of misdiagnosed cases. Diffusion-weighted imaging (DWI) with a b-value of 1000 and apparent diffusion coefficient (ADC) maps provide early and accurate detection of abscess and pus collection. Pyogenic infections are classified into four types of extension based on MRI and DWI findings: (1) epidural/paraspinal abscess with spondylodiscitis, (2) epidural/paraspinal abscess with facet joint infection, (3) epidural/paraspinal abscess without concomitant spondylodiscitis or facet joint infection and (4) intradural abscess (subdural abscess, purulent meningitis and spinal cord abscess). DWI easily detects abscesses and demonstrates the extension, multiplicity and remote disseminated infection. DWI is often a key image in the differential diagnosis. Important differential diagnoses include epidural, subdural or subarachnoid haemorrhage, cerebrospinal fluid leak, disc herniation, synovial cyst, granulation tissue, intra- or extradural tumour and post-surgical fluid collections. DWI and the ADC values are affected by susceptibility artefacts, incomplete fat suppression and volume-averaging artefacts. Recognition of artefacts is essential when interpreting DWI of spinal and paraspinal infections. DWI is not only useful for the diagnosis but also for the treatment planning of pyogenic and non-pyogenic spinal infections.

Therapy monitoring of skeletal metastases with whole-body diffusion MRI

Current methods of assessing tumor response at skeletal sites with metastatic disease use a combination of imaging tests, serum and urine biochemical markers, and symptoms assessment. These methods do not always enable the positive assessment of therapeutic benefit to be made but instead provide an evaluation of progression, which then guides therapy decisions in the clinic. Functional imaging techniques such as whole-body diffusion magnetic resonance imaging (MRI) when combined with anatomic imaging and other emerging "wet" biomarkers can improve the classification of therapy response in patients with metastatic bone disease. A range of imaging findings can be seen in the clinic depending on the type of therapy and duration of treatment. Successful response to systemic therapy is usually depicted by reductions in signal intensity accompanied by apparent diffusion coefficient (ADC) increases. Rarer patterns of successful treatment include no changes in signal intensity accompanying increases in ADC values (T2 shine-through pattern) or reductions in signal intensity without ADC value changes. Progressive disease results in increases in extent/intensity of disease on high b-value images with variable ADC changes. Diffusion MRI therapy response criteria need to be developed and tested in prospective studies in order to address current, unmet clinical and pharmaceutical needs for reliable measures of tumor response in metastatic bone disease.

Paediatric acquired pathological vertebral collapse

Vertebral collapse is a significant event in the paediatric patient with a real potential for associated deformity and morbidity. While in adults the causes tend towards the malignant, particularly metastatic and metabolic disease, the paediatric population demonstrates a different range of diagnoses. This article reviews the typical imaging findings of the more common underlying acquired pathological causes of vertebral collapse in children, including Langerhans cell histiocytosis, chronic recurrent multifocal osteomyelitis, osteogenesis imperfecta. Other causes include pyogenic osteomyelitis and tuberculosis and neoplastic lesions, either primary, metastatic or of haematological origin.

Assessing the relation between bone marrow signal intensity and apparent diffusion coefficient in diffusion-weighted MRI

OBJECTIVE

The purposes of this study were to observe the relation between signal intensity (SI) on MR images with a high b value and the apparent diffusion coefficient (ADC) of bone marrow on body diffusion-weighted MR images, to determine cutoff values that enable separation of malignant and normal bone marrow, and to identify the upper ADC values of untreated multiple myeloma lesions and bone metastatic lesions of breast cancer.

MATERIALS AND METHODS

Retrospective evaluations of 16 patients without bone disease, 21 patients with untreated metastases of breast cancer, and 12 patients with myeloma undergoing body diffusion-weighted MRI were performed (b values, 50 s/mm(2) and 800 or 900 s/mm(2)). Normal yellow and red bone marrow regions were compared with metastatic breast and myeloma bone marrow lesions (one to five regions of interest per patient). SI values were normalized to kidney, muscle, and spinal cord SI. Signal-to-noise ratio and ADC for each lesion were recorded. Nonparametric, receiver operating characteristic, and nonlinear regression analyses were performed.

RESULTS

Yellow bone marrow and red bone marrow ADC values were lower than the tumor values (p < 0.001; area under the curve, 0.94; cutoff, 774 μm(2)/s). Tissue-normalized SI and the signal-to-noise ratio of normal bone marrow were also lower than those in tumor regions (p < 0.001; area under the curve, 0.86-0.88). Second-order polynomial curve fitting between SI and ADC was observed (muscle normalized SI, R(2) = 0.4). The 95th percentile and maximum values for mean tumor ADC distribution were 1209 μm(2)/s and 1433 μm(2)/s.

CONCLUSION

Both tissue-normalized SI and ADC measurements allow differentiation between normal bone marrow and tumors of myeloma and breast cancer. The presence of a nonlinear relation between bone marrow SI and ADC values enables definition of an upper limit of ADC value for untreated myeloma lesions and metastatic lesions of breast cancer.

Whole-body diffusion-weighted MR imaging in cancer: current status and research directions

Diffusion-weighted (DW) magnetic resonance (MR) imaging is emerging as a powerful clinical tool for directing the care of patients with cancer. Whole-body DW imaging is almost at the stage where it can enter widespread clinical investigations, because the technology is stable and protocols can be implemented for the majority of modern MR imaging systems. There is a continued need for further improvements in data acquisition and analysis and in display technologies. Priority areas for clinical research include clarification of histologic relationships between tissues of interest and DW MR imaging biomarkers at diagnosis and during therapy response. Because whole-body DW imaging excels at bone marrow assessments at diagnosis and for therapy response, it can potentially address a number of unmet clinical and pharmaceutical requirements. There are compelling needs to document and understand how common and novel treatments affect whole-body DW imaging results and to establish response criteria that can be tested in prospective clinical studies that incorporate measures of patient benefit.

Diffusion-weighted imaging (DWI) in musculoskeletal MRI: a critical review

Magnetic resonance imaging (MRI) is the mainstay of diagnosis, staging and follow-up of much musculoskeletal pathology. Diffusion-weighted magnetic resonance imaging (DWI) is a recent addition to the MR sequences conventionally employed. DWI provides qualitative and quantitative functional information concerning the microscopic movements of water at the cellular level. A number of musculoskeletal disorders have been evaluated by DWI, including vertebral fractures, bone marrow infection, bone marrow malignancy, primary bone and soft tissue tumours; post-treatment follow-up has also been assessed. Differentiation between benign and malignant vertebral fractures by DWI and monitoring of therapy response have shown excellent results. However, in other pathologies, such as primary soft tissue tumours, DWI data have been inconclusive in some cases, contributing little additional information beyond that gained from conventional MR sequences. The aim of this article is to critically review the current literature on the contribution of DWI to musculoskeletal MRI.

Diffusion-weighted imaging for non-invasive and quantitative monitoring of bone marrow infiltration in patients with monoclonal plasma cell disease: a comparative study with histology

Bone marrow plasma cell infiltration is a crucial parameter of disease activity in monoclonal plasma cell disorders. Until now, the only way to quantify such infiltration was bone marrow biopsy or aspiration. Diffusion-weighted imaging (DWI) is a magnetic resonance imaging-technique that may mirror tissue cellularity by measuring random movements of water molecules. To investigate if DWI is capable of assessing bone marrow cellularity in monoclonal plasma cell disease, we investigated 56 patients with multiple myeloma or monoclonal gammopathy of undetermined significance, and 30 healthy controls using DWI of the pelvis and/or the lumbar spine. In 25 of 30 patients who underwent biopsy, bone marrow trephine and DWI could be compared. Of the patients with symptomatic disease 15 could be evaluated after systemic treatment. There was a positive correlation between the DWI-parameter apparent diffusion coefficient (ADC) and bone marrow cellularity as well as micro-vessel density (P<0·001 respectively). ADC was significantly different between patients and controls (P<0·01) and before and after systemic therapy (P<0·001). In conclusion, DWI enabled bone marrow infiltration to be monitored in a non-invasive, quantitative way, suggesting that after further investigations on larger patient groups this might become an useful tool in the clinical work-up to assess tumour burden.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and diffusion-weighted imaging of bone marrow in healthy individuals

BACKGROUND

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) displays microcirculation and permeability by application of contrast-media and diffusion-weighted imaging (DWI) is a tool for quantification of cellularity in the investigated area. Recently published examples cover breast cancer, CNS tumors, head and neck cancer, gastrointestinal cancer, prostate cancer as well as hematologic malignancies.

PURPOSE

To investigated the influence of age, sex, and localization of the investigated region on findings of DCE-MRI and DWI.

MATERIAL AND METHODS

DCE-MRI-parameters amplitude A and exchange rate constant kep as well as the DWI-parameter ADC of the bone marrow of the lumbar vertebral column of 30 healthy individuals covering the typical range of age of tumor patients were evaluated. ADC was calculated using b=0 and a maximal b value of either 400 or 750 s/mm(2).

RESULTS

Amplitude A of DCE-MRI decreased with age (P = 0.01) and amplitude A, exchange rate constant kep as well as ADC based on b = 400 s/mm(2) and b = 750 s/mm(2,) respectively, decreased significantly from the first to the fifth lumbar vertebra with P = 0.02, P = 0.05, P = 0.003, and P = 0.002, respectively.

CONCLUSION

Quantitative parameters of functional imaging techniques in bone marrow are influenced by the age of the examined individual and the anatomical location of the investigated region.

Diffusion magnetic resonance imaging to differentiate degenerative from infectious endplate abnormalities in the lumbar spine

STUDY DESIGN

A retrospective observational study of healthy volunteers and patients with degenerative and infectious endplate abnormalities in the lumbar spine.

OBJECTIVES

Our purpose was to evaluate the usefulness of diffusion-weighted imaging (DWI) for the differentiation of degenerative and infectious endplate abnormalities using 1.5-T magnetic resonance imaging (MRI).

SUMMARY OF BACKGROUND DATA

DWI can provide valuable structural information about tissues that may be useful for clinical applications in differentiation between degenerative and infectious endplate abnormalities.

METHODS

Sixteen consecutive patients with endplate abnormalities that was detected by MRI of the lumbar spine, and 15 healthy volunteers were studied. DWI was performed using whole-body imaging with background body signal suppression with a b value of 1000 s/mm2. Apparent diffusion coefficient values of normal and abnormal vertebral bone marrow were calculated.

RESULTS

Twenty-nine vertebral abnormalities were found in 16 patients. Nine vertebral abnormalities in 5 patients were because of infections and 20 vertebral abnormalities in 11 patients were because of degenerative changes; 7 levels were classified as Modic type 1, 7 levels as type 2, and 6 levels as type 3. DWI showed hyperintensity in all patients with infection, similar to that used in positron emission tomography, but not in the intervertebral spaces of any patients with degenerative disease. Apparent diffusion coefficient values of infectious bone marrow were significantly higher than normal and degenerative bone marrow.

CONCLUSION

DWI is useful for differentiation of degenerative and infectious endplate abnormalities. Moreover, MRI is widely used clinically because of the lack of ionizing radiation, low cost, and fast imaging time as compared with positron emission tomography. Therefore, DWI has the potential to be used as a screening tool.

A comparative study of pyogenic and tuberculous spondylodiscitis

STUDY DESIGN

We performed a retrospective review of 126 cases of infectious spondylodiscitis over a 4-year period.

OBJECTIVE

Differentiation between pyogenic spondylodiscitis (PS) and tuberculous spondylodiscitis (TS) is essential for deciding on the appropriate therapeutic regimen. The aim of this study was to compare the characteristics of the 2 forms of spondylodiscitis.

SUMMARY OF BACKGROUND DATA

There has been much effort to distinguish the radiologic findings in PS versus TS, but classification based on radiologic findings alone had limitations yet.

METHODS

We compared the predisposing factors or associated illnesses, clinical, radiologic, and laboratory features of microbiologically confirmed cases of PS and TS in 2 university hospitals.

RESULTS

Of 126 patients, 79 had PS and 47 TS. PS was more frequently associated with the followings: previous invasive spinal procedures (PS vs. TS: 32.9% vs. 8.5%), preceding bacteremia (13.9% vs. 0%), chronic renal failure (12.7% vs. 0%), liver cirrhosis (13.9% vs. 0%), fever (temperature >38°C) (48.1% vs. 17.0%), white blood cell counts over 10,000/mm (41.8% vs. 19.1%), fraction of neutrophils >75% (49.4% vs. 27.7%), C-reactive protein levels over 5 mg/dL (58.2% vs. 27.7%), erythrocyte sedimentation rate levels over 40 mm/h (84.4% vs. 66.0%), and ALP levels over 120 IU/L (45.6% vs. 17.0%). TS was frequently associated with active tuberculosis of other organs (0% vs. 31.9%), longer diagnostic delay (47.6 vs. 106.3 days), involvement of thoracic spines (21.5% vs. 38.3%), and involvement of ≥3 spinal levels (11.4% vs. 36.2%).

CONCLUSION

Previous invasive spinal procedures, preceding bacteremia, fever, higher white blood cell counts, C-reactive protein, ALP, and higher fraction of neutrophils are suggestive of PS. Concurrent active tuberculosis, more indolent course and involvement of thoracic spines are suggestive of TS. When the causative organism is not identified despite all efforts at diagnosis, combination of the clinical, radiologic, and laboratory characteristics of the patient is helpful.

[Diffusion-weighted MR imaging of the spine and cord]

Due to its excellent sensitivity, MR imaging is invaluable for the evaluation of lesions of the cord and spine. Several studies dedicated to diffusion-weighted MR evaluation of the cord and spine have been published. While diffusion-weighted MR imaging of the brain is routinely performed, it is seldom performed when imaging the spine due to serious limitations. While anatomical limitations may not be changed, the voxel size, phase-encoding direction, mode of k-space filling, and acceleration factor are all parameters that can be optimized in order to routinely obtain diffusion-weighted imaging of the spine on 1.5T and 3T scanners.

Whole-body MR imaging, bone diffusion imaging: how and why?

Whole-body MRI (W-B MRI) and diffusion-weighted imaging (DWI) are two novel techniques that greatly facilitate the evaluation of many disorders of childhood. In the musculoskeletal system, these techniques primarily aid in the evaluation of the marrow, although there is increasing interest in the study of soft-tissue abnormalities with W-B MRI and of cartilage with DWI.The normal pattern of marrow transformation affects both modalities throughout childhood. Haematopoietic marrow has a much higher signal intensity than fatty marrow on W-B MRI short tau inversion recovery (STIR) images (Darge et al. Eur J Radiol 68:289-298, 2008). Diffusion is greater in haematopoietic marrow than in fatty marrow and decreases in the skeleton with age (Jaramillo et al. Pediatr Radiol 34:S48, 2004). It is important therefore to remember that the entire skeleton is haematopoietic at birth and that there is a process of marrow transformation to fatty marrow. Marrow conversion proceeds from the fingers to the shoulders and from the toes to the hips. Within each bone, fatty marrow transformation begins in the epiphyses, and within the shaft of the long bones fatty marrow transformation begins at the diaphysis and proceeds towards the metaphyses.

Brucellar spondylodiscitis: magnetic resonance imaging features with conventional sequences and diffusion-weighted imaging

PURPOSE

In this retrospective study, we evaluated the contribution and role of diffusion-weighted imaging (DWI) in differentiating acute and chronic forms of brucellar spondylodiscitis. We also describe the characteristics and some indistinguishable features of brucellar spondylodiscitis on magnetic resonance imaging (MRI) to emphasise the importance and limitations of MRI.

MATERIALS AND METHODS

MRI examinations of 25 patients with brucellar spondylodiscitis were retrospectively reviewed and analysed by two experienced radiologists. Signal and morphological changes were assessed. The imaging characteristics of acute and chronic forms of spondylodiscitis were compared. Both discriminative imaging findings of brucellar spondylodiscitis and some uncommon findings were interpreted.

RESULTS

Of 25 patients with spinal brucellosis, eight had thoracic, ten had lumbar, five had both thoracic and lumbar and two had both lumbar and sacral vertebral involvement. We detected posterior longitudinal ligament elevation in 11 patients, epidural abscess formation in 11 and paravertebral abscess formation in nine. Ten patients had cord compression and eight had root compression. Three patients had facet-joint involvement, and one had erector spinae muscle involvement. Eight patients (32%) were in the acute stage, six (24%) in the subacute stage and 11 (44%) in the chronic stage. Vertebral bodies, vertebral end plates and intervertebral disc spaces were hypointense and hyperintense in the acute stage, whereas they were hypointense and heterogeneous in the subacute and chronic stages on T1- and T2-weighted images, respectively. In the acute stage on the DWI series, vertebral bodies, end plates and discs were all hyperintense but hypointense in the chronic stage.

CONCLUSIONS

Although conventional MRI has several advantages over other imaging modalities and is very useful in the differential diagnosis between brucellar spondylodiscitis and other spinal pathologies, it has some difficulties in discriminating acute and chronic forms of spondylodiscitis. DWI is a sensitive, fast sequence that has the potential for differentiating acute and chronic forms of spondylodiscitis, which makes it crucial in spinal imaging.

Diffusion-weighted MR imaging in musculoskeletal radiology: applications in trauma, tumors, and inflammation

Diffusion-weighted imaging is a noninvasive magnetic resonance technique that is capable of measuring icroscopic movement of water molecules (ie, random or Brownian motion) within biologic tissues. Diffusion weighting is achieved with a pulsed-field gradient that leaves "static" spins unaffected but causes dephasing of spin ensembles that experience different motion histories according to their diffusion paths, with respect to the direction of the gradient. This article focuses on the interesting opportunities of the use of diffusion weighted imaging in the diagnosis of musculoskeletal diseases, including trauma, tumor, and inflammation.

Role of diffusion-weighted MRI in the detection of early active sacroiliitis

OBJECTIVE

This study proposed to evaluate the value of diffusion-weighted MRI (DWI) to detect active inflammatory changes in the sacroiliac joints of patients with early axial spondyloarthritis (also spelled spondylarthritis).

SUBJECTS AND METHODS

Forty-two patients with chronic low back pain underwent clinical and MRI evaluation for axial spondyloarthritis or early ankylosing spondylitis. STIR, contrast-enhanced T1-weighted, fat-saturated T2-weighted, and diffusion-weighted (b values: 100, 600, 1,000 s/mm(2)) images were obtained. The presence of subchondral bone marrow edema, subchondral fatty marrow infiltration, or contrast enhancement in the sacroiliac joints or adjacent enthesitis sites was considered a marker for active inflammatory changes. All MRI sequences were evaluated for the presence of acute inflammatory changes and inter- and intrarater reliability of the sequences. Mean apparent diffusion coefficient (ADC) values of diffusion-weighted images were calculated from normal and involved iliac and sacral bones of sacroiliac joints.

RESULTS

ADC values measured from the lesions at b values of 1,000 and 600 s/mm(2) in patients with sacroiliitis (n = 13) were significantly higher than values measured from iliac and sacral bones in patients with low back pain of mechanical origin (n = 29). DWI showed sensitivity for detecting acute lesions in early sacroiliitis similar to that of T1-weighted gadolinium images (area under the curve, 0.843-0.971). Intra- and interrater reliability of DWI was acceptable.

CONCLUSION

DWI is a sensitive, fast sequence and does not require a contrast agent, which makes it a good and cost-effective alternative for imaging sacroiliac joints. DWI also offers the possibility of quantifying diffusion coefficients of the lesions, which helps to discriminate between normal and involved subchondral bone.

Monitoring ankylosing spondylitis therapy by dynamic contrast-enhanced and diffusion-weighted magnetic resonance imaging

OBJECTIVE

The effects of different therapies on enthesitis/osteitis in active ankylosing spondylitis (AS) were evaluated by magnetic resonance imaging (MRI). The aim was to assess the role of quantitative MRI in the evaluation of AS treatment efficacy.

MATERIALS AND METHODS

Thirty patients with active spondylitis or bilateral sacroiliitis were selected and followed up for 1 year. Ten of the patients were treated only with non-steroidal anti-inflammatory drugs, 10 patients additionally received at baseline an intravenous pulse of glucocorticoids and 10 patients were treated with regular infusions of infliximab. Disease activity was measured according to clinical instruments and laboratory tests. For each patient, one selected inflamed lesion was followed from baseline through control visits quantitatively by diffusion-weighted imaging (DWI) measuring the apparent diffusion coefficient (ADC) and by dynamic contrast-enhanced imaging (DCEI) with evaluation of the enhancement factor (f(enh)) and enhancement gradient (g(enh)).

RESULTS

Clinical and quantitative MRI parameters diminished significantly with regression of the inflammatory activity. The improvement in AS was most pronounced in patients treated with infliximab; after 12 months the ADC diminished from an average of 1.31 to 0.88 x 10(-3) mm(2)/s, f(enh) from 1.85 to 0.60, and g(enh) from 3.09 to 1.40 %/s.

CONCLUSION

Diffusion-weighted imaging and DCEI were shown to be effective in quantifying changes in inflammation in skeletal lesions during the treatment of AS, and could therefore be convenient for assessing treatment efficacy. To the best of our knowledge this is the first time DWI was used to evaluate the activity of skeletal inflammation in rheumatic diseases such as AS.

Diffusion-weighted imaging of the appendicular skeleton with a non-Carr-Purcell-Meiboom-Gill single-shot fast spin-echo sequence

OBJECTIVE

The objective of our study was to prospectively evaluate the signal-to-noise ratio (SNR) improvement in diffusion-weighted imaging (DWI) of the appendicular skeleton with the use of a newly developed non-Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo (SSFSE) sequence and to evaluate its effect on apparent diffusion coefficient (ADC) measurements.

SUBJECTS AND METHODS

DWI of the bone was performed in 32 patients with an echo-planar imaging (EPI)-based sequence followed by a non-CPMG SSFSE technique. SNR and ADC values were measured over a lesion-free right femoral head. A score was assigned for each set of images to assess image quality. When a bone lesion was present, contrast-to-noise ratio (CNR) and ADC were also measured. Paired Student's t tests were used for statistical analysis.

RESULTS

The mean (+/- SD) SNR values were 9.89 +/- 2.20 and 81.68 +/- 4.87 for EPI and non-CPMG SSFSE DWI, respectively. SNR values associated with the non-CPMG SSFSE technique were found to be significantly higher than those measured with the EPI-based DWI technique (p < 0.01). Mean ADCs of the bone were 0.57 +/- 0.20 and 0.29 +/- 0.15 x 10(-3) mm2/s, respectively, for EPI and non-CPMG SSFSE DWI. Image quality scores were higher for the non-CPMG SSFSE DWI technique (p < 0.05) than for the EPI-based DWI technique. Overall lesion CNR was found to be higher in DWI performed with the non-CPMG SSFSE technique.

CONCLUSION

The non-CPMG SSFSE technique provides a significant improvement over the currently used EPI-based DWI technique and has the potential to be a powerful tool in imaging the appendicular skeleton.

Diffusion weighted imaging in osteoradiology

Diffusion weighted imaging gained attention as an imaging modality, which provides information on the microstructure of a tissue, which can be used for tissue characterization. This is of importance in patients where other diagnostic tools provide equivocal or unspecific information. In addition quantitative diffusion measurements provide objective parameters for unbiased comparison of treatment response, which is mandatory for therapy monitoring. Technical restriction limited the use of Diffusion Weighted Imaging to the brain. However, with the improvement in scanner technology and the availability of new MR sequences investigation of the Muskulo Skeletal System was made possible. We describe the potential of Diffusion Weighted Imaging as a non-invasive technique to evaluate pathological, inflammatory and physiological processes in osteoradiology.

Feasibility of a RARE-based sequence for quantitative diffusion-weighted MRI of the spine

The feasibility of a diffusion-weighted single-shot fast-spin-echo sequence for the diagnostic work-up of bone marrow diseases was assessed. Twenty healthy controls and 16 patients with various bone marrow pathologies of the spine (bone marrow edema, tumor and inflammation) were examined with a diffusion-weighted single-shot sequence based on a modified rapid acquisition with relaxation enhancement (mRARE) technique; four diffusion weightings (b-values: 50, 250, 500 and 750 s/mm(2)) in three orthogonal orientations were applied. Apparent diffusion coefficients (ADCs) were determined in the bone marrow and in the intervertebral discs of healthy volunteers and in diseased bone marrow. Ten of the 20 volunteers were repeatedly scanned within 30 min to examine short-time reproducibility. Spatial reproducibility was assessed by measuring ADCs in two different slices including the same lesion in 12 patients. The ADCs of the lesions exhibited significantly higher values, (1.27 +/- 0.32)x10(-3) mm(2)/s, compared with healthy bone marrow, (0.21 +/- 0.10)x10(-3) mm(2)/s. Short-time and spatial reproducibility had a mean coefficient of variation of 2.1% and 6.4%, respectively. The diffusion-weighted mRARE sequence provides a reliable tool for determining quantitative ADCs in vertebral bone marrow with adequate image quality.