[Differentiation of benign osteoporotic and neoplastic vertebral compression fractures with a diffusion-weighted, steady-state free precession sequence]

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.

Magnetic resonance imaging of the spinal marrow: Basic understanding of the normal marrow pattern and its variant

For now, magnetic resonance (MR) is the best noninvasive imaging modality to evaluate vertebral bone marrow thanks to its inherent soft-tissue contrast and non-ionizing nature. A daily challenging scenario for every radiologist interpreting MR of the vertebral column is discerning the diseased from normal marrow. This requires the radiologist to be acquainted with the used MR techniques to judge the spinal marrow as well as its normal MR variants. Conventional sequences used basically to image marrow include T1W, fat-suppressed T2W and short tau inversion recovery (STIR) imaging provides gross morphological data. Interestingly, using non-routine MR sequences; such as opposed phase, diffusion weighted, MR spectroscopy and contrasted-enhanced imaging; may elucidate the nature of bone marrow heterogeneities; by inferring cellular and chemical composition; and adding new functional prospects. Recalling the normal composition of bone marrow elements and the physiologic processes of spinal marrow conversion and reconversion eases basic understanding of spinal marrow imaging. Additionally, orientation with some common variants seen during spinal marrow MR imaging as hemangiomas and bone islands is a must. Moreover, awareness of the age-associated bone marrow changes as well as changes accompanying different variations of the subject’s health state is essential for radiologists to avoid overrating normal MR marrow patterns as pathologic states and metigate unnecessary further work-up.

[Differentiation between acute osteoporotic and metastatic vertebral body fractures by imaging]

OBJECTIVES

This article discusses the morphological criteria for the differentiation between acute osteoporotic and metastatic vertebral body fractures and new imaging methods, such as diffusion-weighted and chemical shift magnetic resonance imaging (MRI) are presented.

BACKGROUND

The differential diagnostics of osteoporotic and metastatic vertebral body fractures can be difficult in some cases. Both entities normally occur without adequate trauma and predominantly in elderly patients.

IMAGING

Conventional X-ray examination is the initial imaging method of choice but is not able to reliably differentiate between the osteoporotic or metastatic etiology of a fracture. Computed tomography (CT) clearly depicts osseous destruction in metastatic fractures but lacks specificity. Magnetic resonance imaging (MRI) shows a higher sensitivity and specificity in differentiating osteoporotic and metastatic fractures.

DIFFERENTIAL DIAGNOSTICS

The combination CT and MRI allows an accurate diagnosis with respect to an osteoprorotic or metastatic etiology in most of cases but bone marrow edema in acute fractures sometimes leads to ambiguous results and differential diagnostic problems.

Bone abnormal signal incidentally found in pre-biopsy diffusion-weighted MRI for suspected prostate cancer: what does it reflect?

OBJECTIVE

To clarify the clinical significance of incidentally found diffusion-weighted MRI (DW-MRI)-positive findings on pre-biopsy MRI in patients with suspected prostate cancer.

PATIENTS AND METHODS

754 consecutive patients with suspected prostate cancer underwent pelvic MRI including DW-MRI. 43 DW-MRI-positive bone lesions were found in 27 patients. Imaging findings of these lesions were compared with the clinical diagnosis.

RESULTS

Of the 43 DW-MRI-positive bone lesions, 21 (48.8%) were diagnosed as metastatic prostate cancer. The remaining 22 (51.2%) were diagnosed as red bone marrow in 17, enchondroma in 1, ganglion in 1, osteoma in 1, fibrous dysplasia in 1 and bone infarction in 1. Enchondroma, ganglion, osteoma and fibrous dysplasia all showed T1-weighted imaging (T1WI) low and T2-weighted imaging (T2WI) high signals, while others, including prostate cancer metastases, showed T1WI and T2WI low signals. Of the 40 lesions with T1WI and T2WI low signals, metastatic prostate cancer had higher apparent diffusion coefficient values (median 0.42 × 10(-3) mm(2)/s) than other lesions (0.26 × 10(-3) mm(2)/s; p < 0.0001).

CONCLUSIONS

DW-MRI-positive bone lesions represent various coexisting types of bone lesions, including metastatic cancer in patients with suspected prostate cancer. T2WI findings and apparent diffusion coefficient values can be helpful in diagnosing metastatic cancer.

Differentiation of acute osteoporotic and malignant compression fractures of the spine: use of additive qualitative and quantitative axial diffusion-weighted MR imaging to conventional MR imaging at 3.0 T

PURPOSE

To retrospectively determine the value of adding qualitative and quantitative axial diffusion-weighted (DW) imaging to standard spine magnetic resonance (MR) imaging to differentiate between acute osteoporotic and malignant compression fractures at 3.0 T.

MATERIALS AND METHODS

The institutional ethics committee approved this retrospective study and waived the requirement to obtain informed consent. The authors retrospectively analyzed 3.0-T MR images, including DW images (b values: 0, 800, and 1400 sec/mm(2)), in 62 patients with acute compression fractures. Three radiologists independently interpreted MR images for the presence of malignancy by using conventional MR images alone and in combination with axial DW images with qualitative and quantitative analysis. Apparent diffusion coefficients (ADCs) were measured within solid portion with careful use of a small region of interest (ROI). The Mann-Whitney U test was performed.

RESULTS

There were 30 malignant and 32 acute osteoporotic compression fractures. At qualitative analysis, hyperintensity relative to spinal cord was more frequent in malignant compression fractures than in acute osteoporotic compression fractures (87% vs 22%, respectively; P < .001). Median ADCs of malignant fractures were significantly lower than those of benign fractures (P < .001). With conventional MR imaging alone, sensitivity, specificity, and accuracy were 100%, 94%, and 97%, respectively, for reader 1; 97%, 78%, and 87% for reader 2; and 100%, 84%, and 92% for reader 3. With conventional and DW MR imaging combined, sensitivity, specificity, and accuracy were 100%, 97%, and 98% for all three readers. The addition of DW imaging led to correct changes in diagnosis: Reader 1 improved by 1.6% (one of 62 fractures), reader 2 improved by 11% (seven of 62 fractures), and reader 3 improved by 6.5% (four of 62 fractures).

CONCLUSION

The addition of axial DW imaging to a conventional MR imaging protocol improved diagnostic accuracy in the differentiation of acute osteoporotic from malignant compression fractures by measuring ADCs in the solid portion with careful use of a small ROI.

Research synthesis: what is the diagnostic performance of magnetic resonance imaging to discriminate benign from malignant vertebral compression fractures? Systematic review and meta-analysis

STUDY DESIGN

This study is a research synthesis of the published literature evaluating the performance of magnetic resonance imaging (MRI) for differentiation of malignant from benign vertebral compression fractures (VCFs).

OBJECTIVE

Perform a systematic review and meta-analysis to summarize and combine the published data on MRI for discriminating malignant from benign VCFs.

SUMMARY OF BACKGROUND DATA

The differentiation between benign and malignant VCFs in the spine is a challenging problem confronting spine practitioners.

METHODS

MEDLINE, EMBASE, and other databases were searched by 2 independent reviewers to identify studies that reported the performance of MRI for discriminating malignant from benign VCF. Included studies were assessed for described MRI features and study quality. The sensitivity, specificity, and diagnostic odds ratio (OR) of each feature were pooled with a random-effects model weighted by the inverse of the variance of each individual estimate.

RESULTS

A total of 31 studies with 1685 subjects met the selection criteria. All the studies focused on describing specific features rather than overall diagnostic performance. Signal intensity ratio on opposed phase (chemical shift) imaging 0.8 or more (OR = 164), apparent diffusion coefficient on echo planar diffusion-weighted images 1.5 × 10(-3) mm2/s or less with b value 500 s/mm2 (OR = 130), presence of other noncharacteristic vertebral lesions (OR = 55), presence of paraspinal mass (OR = 33), involvement of posterior element (OR = 28), involvement of pedicle (OR = 24), complete replacement of normal bone marrow in VCF (OR = 19), presence of epidural mass (OR = 13), and diffuse convexity of posterior vertebral border (OR = 10) were associated with malignant VCFs, whereas coexisting healed benign VCF (OR = 0.006), presence of "fluid sign" (OR = 0.08), presence of focal posterior vertebral border convexity/retropulsion (OR = 0.08), and band-like shape of abnormal signal (OR = 0.07) were associated with benign VCFs.

CONCLUSION

Several specific MRI features using signal intensity characteristics, morphological characteristics, quantitative techniques, and findings at other levels can be useful for distinguishing benign from malignant VCFs and can serve as inputs for a prediction model. Observer performance reliability has not been adequately assessed.

Diffusion-weighted MR imaging in differentiation between osteoporotic and neoplastic vertebral fractures

PURPOSE

To assess the usefulness of magnetic resonance imaging (MRI) with spin-echo echo-planar diffusion-weighted imaging (SE-EPI-DWI) in differentiation between vertebral osteoporotic fractures and pathological neoplastic fractures.

MATERIALS AND METHODS

Thirty-three patients with both osteoporotic or neoplastic vertebral fractures diagnosed with X-ray or TC were studied with MRI exam, (1.5 T unit) with DWI sequences. DWI sequences were qualitatively analyzed. Apparent diffusion coefficient (ADC) values were also determined and compared to the definitive histologic diagnosis.

RESULTS

DWI of neoplastic lesions showed hyperintensity signal in 22 out of 23 cases. Mean ADC value of neoplastic fractures was 1.241 ± 0.4 × 10(-3) mm(2)/s; mean ADC value of osteoporotic fractures was 0.646 ± 0.368 × 10(-3) mm(2)/s. Neoplastic fractures showed ADC values significantly higher than osteoporotic ones (p < 0.001). DWI imaging and histology showed a significant correlation.

CONCLUSION

DWI provides reliable information to support MRI diagnosis of neoplastic versus osteoporotic fractures. ADC value appears as a useful adjunctive parameter.

Quantitative analysis of the diffusion-weighted steady-state free precession signal in vertebral bone marrow lesions

OBJECTIVES

: Diffusion-weighted steady-state free precession (DW-SSFP) sequences have shown great potential for the differential diagnosis of benign osteoporotic and malignant neoplastic vertebral compression fractures, which appear hypo- to isointense or hyperintense in DW-SSFP magnetic resonance imaging, respectively. In contrast to other diffusion weighting sequences, the DW-SSFP signal depends not only on the apparent diffusion coefficient (ADC), but also on the tissue relaxation times and sequence parameters. The purpose of the present study was to provide a detailed analysis of the DW-SSFP signal in benign and malignant vertebral lesions (VLs) and in vertebral bone marrow (VBM) to understand the observed signal alterations and their dependence on tissue and sequence parameters.

MATERIALS AND METHODS

: Magnetic resonance imaging was performed in 40 patients with benign (n = 20) or malignant (n = 20) VLs to determine the fat fraction and tissue parameters (ADC, T1, T2, T2*) for both the water and fat signal. With these values, the DW-SSFP signal was simulated and compared with the measured signals for different diffusion gradients by determining the signal intensity ratio between the SSFP signals of the lesions and of normal-appearing VBM for both malignant and benign VLs.

RESULTS

: The simulated DW-SSFP contrast agreed well with the measured contrast and provided a very good differentiation between benign osteoporotic and malignant VLs. ADCs were significantly different in both lesion types (malignant 1.36 vs. osteoporotic 1.77 × 10 mm/s); however, the observed contrast differences were caused predominantly by an opposed-phase readout in combination with significantly different T2* values (malignant 22 vs. osteoporotic 14 ms) and fat fractions (malignant 3.9% vs. osteoporotic 12%) in the lesions as well as significantly different fat fractions in normal-appearing VBM (malignant 42% vs. osteoporotic 52%) of both patient groups.

CONCLUSIONS

: Although the ADCs of the evaluated malignant and benign VLs showed highly significant differences, the influence of diffusion on the DW-SSFP signal contrast is relatively low compared with other tissue parameters due to the very complex signal mechanism of the SSFP sequence. Thus, the observed DW-SSFP signal contrast of different VLs (hypo-/isointense vs. hyperintense signal) is rather fat- and T2*-weighted than diffusion-weighted. The intermediate diffusion weighting of the applied SSFP sequence, however, helps to shift the different contrasts into a signal range that is easily visually accessible.

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.

The role of magnetic resonance imaging in oncology

Conventional diagnostic magnetic resonance imaging (MRI) techniques have focused on improving the spatial resolution and image acquisition speed (whole-body MRI) or on new contrast agents. Most advances in MRI go beyond morphologic study to obtain functional and structural information in vivo about different physiological processes of tumor microenvironment, such as oxygenation levels, cellular proliferation, or tumor vascularization through MRI analysis of some characteristics: angiogenesis (perfusion MRI), metabolism (MRI spectroscopy), cellularity (diffusion-weighted MRI), lymph node function, or hypoxia [blood-oxygen-level-dependent (BOLD) MRI]. We discuss the contributions of different MRI techniques than must be integrated in oncologic patients to substantially advance tumor detection and characterization risk stratification, prognosis, predicting and monitoring response to treatment, and development of new drugs.

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.

Multiparameter MRI assessment of normal-appearing and diseased vertebral bone marrow

OBJECTIVE

To evaluate spin-lattice (T1) and spin-spin (T2) relaxation times as well as apparent diffusion coefficients (ADCs) of the fat and water components in the vertebral bone marrow (vBM) of patients with benign and malignant lesions.

METHODS

Forty-four patients were examined at 1.5 T: there were 24 osteoporotic vertebral fractures (15 women, 9 men; median age: 73, 48-86 years) and 20 malignant vertebral infiltrations (9 women, 11 men; median age: 60, 25-87). Relaxation times were determined separately for the water and the fat component using a saturation-recovery technique for T1 and measurements with variable echo times for T2. ADCs were determined with a diffusion-weighted (DW) echo-planar imaging (EPI) and a single-shot turbo-spin-echo (ssTSE) sequence.

RESULTS

T1 of the water component and ADCs were significantly increased in the lesions compared with normal-appearing vBM (malignant: 1,252 vs. 828 ms, osteoporotic: 1,315 vs. 872 ms). ADCs determined with the DW-ssTSE were significantly increased compared with the DW-EPI. ADCs determined with the DW-ssTSE differed significantly between osteoporotic and malignant lesions (1.74 vs 1.35 x 10⁻³ mm²/s.

CONCLUSIONS

All parameters exhibit significant differences between normal-appearing vBM and the lesions. However, only the ADCs determined with the DW-ssTSE differed significantly between osteoporotic fractures and malignant lesions, potentially allowing for a differential diagnosis of these two entities.

Comparison of diffusion-weighted whole body MRI and skeletal scintigraphy for the detection of bone metastases in patients with prostate or breast carcinoma

PURPOSE

To prospectively compare the diagnostic accuracy of diffusion-weighted whole body imaging with background whole body signal suppression (DWIBS) with skeletal scintigraphy for the diagnosis and differentiation of skeletal lesions in patients suffering from prostate or breast cancer.

MATERIAL AND METHODS

A diagnostic cohort of 36 patients was included in skeletal scintigraphy and 1.5 T DWIBS MRI. Based on morphology and signal intensity patterns, two readers each identified and classified independently, under blinded conditions, all lesions into three groups: (1) malignant, (2) unclear if malignant or benign and (3) benign. Finally, for the definition of the gold standard all available imaging techniques and follow-up over a minimum of 6 months were considered.

RESULTS

Overall, 45 circumscribed bone metastases and 107 benign lesions were found. DWIBS performed significantly better in detecting malignant skeletal lesions in patients with more than 10 lesions (sensitivity: 0.97/0.91) compared to skeletal scintigraphy (sensitivity: 0.48/0.42). No statistical difference could be found between DWIBS (0.58/0.33) and skeletal scintigraphy (0.67/0.58) in the sensitivity values for malignant skeletal lesions in patients with less than 5 lesions. For benign lesions, scintigraphy scored best with a sensitivity of 0.93/0.87 compared to 0.20/0.13 for DWIBS. Interobserver agreement with Cohen's kappa coefficient was calculated as 0.784 in the case of scintigraphy and 0.663 for DWIBS.

CONCLUSION

With respect to staging, in prostate and breast carcinoma, the DWIBS technique is not superior to skeletal scintigraphy, but ranks equally. However, in the cases with many bone lesions, markedly more metastases could be discovered using the DWIBS technique than skeletal scintigraphy.

Steady-state MR imaging sequences: physics, classification, and clinical applications

Steady-state sequences are a class of rapid magnetic resonance (MR) imaging techniques based on fast gradient-echo acquisitions in which both longitudinal magnetization (LM) and transverse magnetization (TM) are kept constant. Both LM and TM reach a nonzero steady state through the use of a repetition time that is shorter than the T2 relaxation time of tissue. When TM is maintained as multiple radiofrequency excitation pulses are applied, two types of signal are formed once steady state is reached: preexcitation signal (S-) from echo reformation; and postexcitation signal (S+), which consists of free induction decay. Depending on the signal sampled and used to form an image, steady-state sequences can be classified as (a) postexcitation refocused (only S+ is sampled), (b) preexcitation refocused (only S- is sampled), and (c) fully refocused (both S+ and S- are sampled) sequences. All tissues with a reasonably long T2 relaxation time will show additional signals due to various refocused echo paths. Steady-state sequences have revolutionized cardiac imaging and have become the standard for anatomic functional cardiac imaging and for the assessment of myocardial viability because of their good signal-to-noise ratio and contrast-to-noise ratio and increased speed of acquisition. They are also useful in abdominal and fetal imaging and hold promise for interventional MR imaging. Because steady-state sequences are now commonly used in MR imaging, radiologists will benefit from understanding the underlying physics, classification, and clinical applications of these sequences.

Diffusion-weighted MRI in the body: applications and challenges in oncology

OBJECTIVE

In this article, we present the basic principles of diffusion-weighted imaging (DWI) that can aid radiologists in the qualitative and quantitative interpretation of DW images. However, a detailed discussion of the physics of DWI is beyond the scope of this article. A short discussion ensues on the technical aspects of performing DWI in the body. The emerging applications of DWI for tumor detection, tumor characterization, distinguishing tumor tissue from nontumor tissue, and monitoring and predicting treatment response are highlighted. The challenges to widespread adoption of the technique for cancer imaging in the body are discussed.

CONCLUSION

DWI derives its image contrast from differences in the motion of water molecules between tissues. Such imaging can be performed quickly without the need for the administration of exogenous contrast medium. The technique yields qualitative and quantitative information that reflects changes at a cellular level and provides unique insights about tumor cellularity and the integrity of cell membranes. Recent advances enable the technique to be widely applied for tumor evaluation in the abdomen and pelvis and have led to the development of whole-body DWI.

MR Imaging Evaluation of the Bone Marrow and Marrow Infiltrative Disorders of the Lumbar Spine

The use of MR imaging in assessing lumbar bone marrow first requires an understanding of the bone marrow's normal composition and the various imaging sequences available for use. One of the most useful sequences is the T1-weighted spin-echo sequence. This sequence may be combined with other sequences such as T2-weighted or diffusion-weighted sequences; techniques such as fat suppression, chemical shift imaging, and contrast-enhanced imaging are discussed. The varying features of normal lumbar marrow related to the normal physiologic changes that occur with aging and with changes in hematopoietic demand are important to understand and are described. The appearances of infiltrative marrow disease are explained on the basis of marrow composition and whether disease causes proliferation, replacement, or depletion of normal marrow components.

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.

Methods and applications of diffusion imaging of vertebral bone marrow

Diffusion-weighted imaging (DWI) is an MRI technique that is sensitive to random water movements at spatial scales far below typical MRI voxel dimensions. DWI is a valuable tool for the diagnoses of diseases that involve alterations in water mobility. In the spine, DWI has proven to be a highly useful method for the differential diagnosis of benign and malignant compression fractures. In these pathologies, the microscopic structure of bone marrow is altered in a very different ways, leading to different water mobility, which can be depicted by DWI. Most of the pulse sequences developed for MRI can be adapted for DWI. However, these DWI-adapted sequences are frequently affected by artifacts, mostly caused by physiological motion. Therefore, the introduction of additional correction techniques, or even the development of new sequences is necessary. The first part of this article describes the principles of DWI and the sequences used for DWI of the spine: spin echo (SE), turbo spin echo (TSE), single-shot echo planar imaging (EPI), and steady-state free precession (SSFP) sequences. In the second part, clinical applications of DWI of the spinal bone marrow are extensively discussed.

Differential diagnosis of focal and diffuse neoplastic diseases of bone marrow in MRI

Magnetic resonance imaging (MRI) has become the preferred imaging modality for the evaluation of malignant disease in the bone marrow. Compared to bone marrow aspiration and biopsy, MRI is noninvasive and provides information by sampling a large volume of bone marrow. Due to disease-related alterations in the composition of bone marrow, MRI provides a very high sensitivity, but lacks specificity for most bone marrow disorders. However, MRI can be a very valuable diagnostic tool properly placed within the clinical context.

Diffusion-weighted imaging of bone marrow: current status

Diffusion-weighted imaging allows for measurement of tissue microstructure and reflects the random motion of water protons. It provides a new method to study bone marrow and bone marrow alterations on the basis of altered water-proton mobility in various diseases. Different diffusion-weighted methods have proved to be capable of differentiating between benign edema and tumorous involvement of bone marrow. It is especially useful for the distinction of acute benign osteoporotic and malignant vertebral compression fractures. Diagnosis is based on the contrast to normal bone marrow. Hypo- or isointensity reflects acute benign collapse, whereas hyperintensity is indicative of the tumorous nature of a fracture. Apparent diffusion coefficients (ADC) are significantly lower in metastatic disease than in bone marrow edema. Furthermore, bone marrow cellularity can be estimated by ADC measurements. Diffusion-weighted imaging might be helpful for monitoring response to therapy in metastatic disease.