Developing spinal column: gadolinium-enhanced MR imaging

Imaging of Bone Marrow: From Science to Practice

The study of the bone marrow may pose important challenges, due to its changing features over the life span, metabolic stress, and in cases of disease or treatment. Bone marrow adipocytes serve as storage tissue, but they also have endocrine and paracrine functions, contributing to local and systemic metabolism.Among different techniques, magnetic resonance (MR) has the benefit of imaging bone marrow directly. The use of advanced MR techniques for bone marrow study has rapidly found clinical applications. Beyond the clinical uses, it has opened up pathways to assess and quantify bone marrow components, establishing the groundwork for further study of its implications in physiologic and pathologic conditions.We summarize the features of the bone marrow as an organ, address the different modalities available for its study, with a special focus on MR advanced techniques and their addition to analysis in recent years, and review some of the challenges in interpreting the appearance of bone marrow.

Hot spot 19 F magnetic resonance imaging of inflammation

Among the preclinical molecular imaging approaches, lately fluorine (¹⁹ F) magnetic resonance imaging (MRI) has garnered significant scientific interest in the biomedical research community, due to the unique properties of fluorinated materials and the ¹⁹ F nucleus. Fluorine is an intrinsically sensitive nucleus for MRI-there is negligible endogenous ¹⁹ F in the body and, thus, no background signal which allows the detection of fluorinated materials as "hot spots" by combined ¹ H/¹⁹ F MRI and renders fluorine-containing molecules as ideal tracers with high specificity. In addition, perfluorocarbons are a family of compounds that exhibit a very high fluorine payload and are biochemically as well as physiologically inert. Perfluorocarbon nanoemulsions (PFCs) are well known to be readily taken up by immunocompetent cells, which can be exploited for the unequivocal identification of inflammatory foci by tracking the recruitment of PFC-loaded immune cells to affected tissues using ¹ H/¹⁹ F MRI. The required ¹⁹ F labeling of immune cells can be accomplished either ex vivo by PFC incubation of isolated endogenous immune cells followed by their re-injection or by intravenous application of PFCs for in situ uptake by circulating immune cells. With both approaches, inflamed tissues can unambiguously be detected via background-free ¹⁹ F signals due to trafficking of PFC-loaded immune cells to affected organs. To extend ¹⁹ F MRI tracking beyond cells with phagocytic properties, the PFC surface can further be equipped with distinct ligands to generate specificity against epitopes and/or types of immune cells independent of phagocytosis. Recent developments also allow for concurrent detection of different PFCs with distinct spectral signatures allowing the simultaneous visualization of several targets, such as various immune cell subtypes labeled with these PFCs. Since ligands and targets can easily be adapted to a variety of problems, this approach provides a general and versatile platform for inflammation imaging which will strongly extend the frontiers of molecular MRI. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Cardiovascular Disease.

Distinguishing soft tissue sarcomas of different histologic grades based on quantitative MR assessment of intratumoral heterogeneity

PURPOSE

To explore the role of intratumoral heterogeneity on MRI assessed by histogram analysis in differentiating soft-tissue sarcomas (STS) of different grades.

MATERIALS AND METHODS

Patients with primary STS undergoing MRI prior to iatrogenic procedures were included retrospectively. The histologic grade was assigned according to Federation Nationale des Centres de Lutte Contre le Cancer grading system. T1WI and T2WI were normalized by dividing mean signal intensity (SI) of contralateral/near unaffected muscles. Contrast-enhanced T1WI was normalized by computing enhancement ratio (ER) map as (SI_post-SI_pre)/SI_pre×100, where SI_pre and SI_post represent SI of each pixel before and after enhancement. A region of interest (ROI) was manually drawn to include entire tumor area on axial slice with largest tumor diameter. Mean, mode, standard deviation, kurtosis and skewness on ROIs were extracted with ImageJ software. ANOVA/Kruskal-Wallis test was used to determine the significance of differences. ROC curve was applied for statistically significant parameters. P value ≤0.05 was considered statistically significant.

RESULTS

Among involved 67 patients, 8 were assigned to grade 1, 38 to grade 2 and 21 to grade 3. Skewness (P =  0.022) and kurtosis (P =  0.035) on ER maps were significantly different among STS of different grades. The optimal cutoffs of skewness and kurtosis on ER maps were -0.488 (AUC[95% CI] 0.747[0.557-0.937]; sensitivity/specificity, 62.5%/86.4%) and 0.762 (AUC[95% CI] 0.684[0.548-0.821]; sensitivity/specificity, 76.2%/56.5%), respectively.

CONCLUSION

Intratumoral heterogeneity on MRI quantitatively displayed by histogram parameters can differentiate STS of different grades. Skewness and kurtosis on ER maps show the capacity.

Reduced field of view echo-planar imaging diffusion tensor MRI for pediatric spinal tumors

OBJECTIVE

Spine MRI is a diagnostic modality for evaluating pediatric CNS tumors. Applying diffusion-weighted MRI (DWI) or diffusion tensor imaging (DTI) to the spine poses challenges due to intrinsic spinal anatomy that exacerbates various image-related artifacts, such as signal dropouts or pileups, geometrical distortions, and incomplete fat suppression. The zonal oblique multislice (ZOOM)-echo-planar imaging (EPI) technique reduces geometric distortion and image blurring by reducing the field of view (FOV) without signal aliasing into the FOV. The authors hypothesized that the ZOOM-EPI method for spine DTI in concert with conventional spinal MRI is an efficient method for augmenting the evaluation of pediatric spinal tumors.

METHODS

Thirty-eight consecutive patients (mean age 8 years) who underwent ZOOM-EPI spine DTI for CNS tumor workup were retrospectively identified. Patients underwent conventional spine MRI and ZOOM-EPI DTI spine MRI. Two blinded radiologists independently reviewed two sets of randomized images: conventional spine MRI without ZOOM-EPI DTI, and conventional spine MRI with ZOOM-EPI DTI. For both image sets, the reviewers scored the findings based on lesion conspicuity and diagnostic confidence using a 5-point Likert scale. The reviewers also recorded presence of tumors. Quantitative apparent diffusion coefficient (ADC) measurements of various spinal tumors were extracted. Tractography was performed in a subset of patients undergoing presurgical evaluation.

RESULTS

Sixteen patients demonstrated spinal tumor lesions. The readers were in moderate agreement (kappa = 0.61, 95% CI 0.30-0.91). The mean scores for conventional MRI and combined conventional MRI and DTI were as follows, respectively: 3.0 and 4.0 for lesion conspicuity (p = 0.0039), and 2.8 and 3.9 for diagnostic confidence (p < 0.001). ZOOM-EPI DTI identified new lesions in 3 patients. In 3 patients, tractography used for neurosurgical planning showed characteristic fiber tract projections. The mean weighted ADCs of low- and high-grade tumors were 1201 × 10-6 and 865 × 10-6 mm2/sec (p = 0.002), respectively; the mean minimum weighted ADCs were 823 × 10-6 and 474 × 10-6 mm2/sec (p = 0.0003), respectively.

CONCLUSIONS

Diffusion MRI with ZOOM-EPI can improve the detection of spinal lesions while providing quantitative diffusion information that helps distinguish low- from high-grade tumors. By adding a 2-minute DTI scan, quantitative diffusion information and tract profiles can reliably be obtained and serve as a useful adjunct to presurgical planning for pediatric spinal tumors.

In vivo monitoring of inflammation after cardiac and cerebral ischemia by fluorine magnetic resonance imaging

BACKGROUND

In this study, we developed and validated a new approach for in vivo visualization of inflammatory processes by magnetic resonance imaging using biochemically inert nanoemulsions of perfluorocarbons (PFCs).

METHODS AND RESULTS

Local inflammation was provoked in 2 separate murine models of acute cardiac and cerebral ischemia, followed by intravenous injection of PFCs. Simultaneous acquisition of morphologically matching proton ((1)H) and fluorine ((19)F) images enabled an exact anatomic localization of PFCs after application. Repetitive (1)H/(19)F magnetic resonance imaging at 9.4 T revealed a time-dependent infiltration of injected PFCs into the border zone of infarcted areas in both injury models, and histology demonstrated a colocalization of PFCs with cells of the monocyte/macrophage system. We regularly found the accumulation of PFCs in lymph nodes. Using rhodamine-labeled PFCs, we identified circulating monocytes/macrophages as the main cell fraction taking up injected nanoparticles.

CONCLUSIONS

PFCs can serve as a "positive" contrast agent for the detection of inflammation by magnetic resonance imaging, permitting a spatial resolution close to the anatomic (1)H image and an excellent degree of specificity resulting from the lack of any (19)F background. Because PFCs are nontoxic, this approach may have a broad application in the imaging and diagnosis of numerous inflammatory disease states.

Postnatal maturation and radiology of the growing spine

Postnatal maturation of the spine is marked by the ossification process and by changes in the shape of the vertebrae, spinal curvature, spinal canal, discs, and bone marrow. Different aspects of the spine's maturation process are demonstrated on the three most common radiologic modalities used to evaluate the spine. Conventional plain spine imaging (plain spine radiography) provides a good initial evaluation of the bony spine. CT provides better bone detail and allows finer evaluation of subtle structures, the soft tissues of the spine (discs, ligaments), and the spinal cord. MRI provides excellent resolution of the bone marrow, ligaments, and discs of the spine, and can be used as an adjunct for evaluating the soft tissue of the spine and intraspinal contents.

Structural and functional imaging of normal bone marrow and evaluation of its age-related changes

A number of noninvasive imaging techniques have been used for the evaluation of bone marrow, including magnetic resonance imaging (MRI) and bone marrow scintigraphy. The appearance of bone marrow on MRI varies considerably depending on the proportion of red and yellow marrow, and the composition of the red marrow and its distribution with relation to age and sex. The composition of bone marrow also can vary under physiological and pathological conditions. MRI is a highly sensitive technique for evaluating the bone marrow, but it is limited in its practical use for whole-body bone marrow screening. Bone marrow scintigraphy with radiolabeled compounds such as technetium-99m-labeled nanocolloid and monoclonal antibodies has the advantage of evaluating the entire bone marrow, and has been used for the diagnosis of various bone marrow disorders. In addition, (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging can be used to evaluate bone marrow metabolism and disease and to provide information about the state of the primary tumor, lymph nodes, and distant metastases. Understanding of the appearance of normal bone marrow, including age- and sex-specific differences with each of these imaging modalities, is essential to permit accurate diagnosis of benign and malignant bone marrow disorders. We present a review of MRI and scintigraphy of normal bone marrow with some emphasis on FDG-PET imaging in assessing marrow activity in normal and abnormal states and also present preliminary data regarding normal age-related changes in bone marrow through use of FDG-PET, as well as the role of segmentation of bone marrow on MRI for quantitative calculation of the metabolic volumetric product for red marrow metabolism using FDG-PET.

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.

Normal Spinal Bone Marrow in Adults: Dynamic Gadolinium-enhanced MR Imaging

PURPOSE

To determine the patterns of dynamic enhancement of normal spinal bone marrow in adults at gadolinium-enhanced magnetic resonance (MR) imaging and the changes that occur with aging.

MATERIALS AND METHODS

Dynamic contrast material-enhanced MR imaging of the thoracolumbar spine was performed in 71 patients. The maximum percentage of enhancement (Emax), enhancement slope, and enhancement washout were determined from bone marrow enhancement time curves (ETCs). The bone marrow signal intensity on T1-weighted spin-echo MR images was qualitatively classified into three grade categories. Quantitative ETC values were correlated with patient age and bone marrow fat content grade. Statistical analysis included mean t test comparison, analysis of variance, and regression analysis of the correlations between age and quantitative MR parameters.

RESULTS

Emax, slope, and washout varied widely among the patients. Emax values were obtained within 1 minute after contrast material injection and ranged from 0% to 430%. Emax values were significantly higher in patients younger than 40 years than in those aged 40 years or older (P <.001). These values decreased with increasing age in a logarithmic relationship (r = 0.71). Emax values decreased as fat content increased, but some overlap among the fat content grades was noted. Analysis of variance revealed that Emax was significantly related to age (younger than 40 years vs 40 years or older) (P <.001) and fat content grade (P <.001) but not significantly related to sex.

CONCLUSION

Dynamic contrast-enhanced MR imaging patterns of normal spinal bone marrow are dependent mainly on patient age and fat content.

Imaging of metabolic bone disease and marrow disorders in children

There are a wide variety of metabolic and infiltrative diseases that involve the bones. Conventional radiography is the primary imaging examination for the initial evaluation of most of these disorders. MR imaging, however, provides detailed information about the bone marrow and is gaining an increasingly important role in the management of disorders of bone marrow infiltration.

Imaging of spinal infection

MR imaging is the modality of choice for the detection, staging, and differential diagnosis of inflammatory disorders of the spine. Infectious spondylitis is characterized by the involvement of two adjacent vertebrae and the intervening disk with severe BME and early destruction of the end plates. The disk space is narrowed and typically exhibits water-equivalent signal intensity on T2-weighted or STIR images. Prevertebral and epidural extensions, abscess formation, enhancement of the BME, the disk space, and the surrounding granulation tissue are well demonstrated by gadolinium-enhanced images. Cervical spondylitis frequently involves more than one level. Bone marrow abnormalities may be subtle at this level and increased signal intensity of the disk space on T2-weighted or STIR images is an important finding. The risk for neurologic complications is increased. Granulomatous infections caused by tuberculosis, brucellosis, fungi, and parasites, including hydatid disease (Echinococcus), are frequently associated with imaging findings different from those seen with nonspecific bacterial infection. In patients with chronic infectious spondylitis, diffuse reactive bone marrow changes with decreased signal intensity on T1-weighted images, increased signal intensity on T2-weighted and STIR images, and increased uptake after gadolinium administration may occur. This phenomenon is probably caused by reactive bone marrow stimulation, simulating diffuse hematologic neoplastic disease. Erosive intervertebral osteochondrosis with bandlike disk gadolinium enhancement and BME, which is commonly associated with local pain, is the most important differential diagnosis of bacterial spondylitis.