Magnetic resonance imaging of the normal bone marrow

The bone marrow is a complex organ that contains fat and nonfat cells, the proportions of which vary greatly with age and in the different bones of the skeleton. Magnetic resonance (MR) imaging provides information on the composition of the medullary cavity of any given bone and on the distribution of red and yellow marrow in the skeleton. This article deals with the wide spectrum of appearances of the normal bone marrow at MR imaging.     

Magnetic resonance imaging of normal bone marrow

The appearance in magnetic resonance imaging (MRI) of the bones depends, to a large extent, on the unmineralized content of the bone cavities. Because yellow marrow contains a large number of fat protons and red marrow a significant number of water protons, MRI offers the opportunity to map the distribution of red and yellow marrow. In addition, red marrow MR appearance varies according to the relative proportion of fat and nonfat cells. Variations in the composition of red marrow and its distribution among normal subjects, mainly in relation to age and sex, contribute to creating a wide spectrum in bone MR appearance, which must be known in order to avoid confusion with bone marrow abnormalities. Received 22 May 1997; Revision received 27 January 1998; Accepted 29 January 1998     

Magnetic resonance imaging of bone marrow disorders

The sensitivity of MRI to marrow infiltration together with the ability to perform multiplanar imaging allows evaluation of the bone marrow in a manner that has never been feasible before. The clinical impact of this has yet to be fully realized. However, detection of focal marrow infiltration by MRI with concurrently normal conventional imaging studies has important clinical implications for staging and therapy. Proper staging of marrow-based neoplasms such as leukemia and lymphoma is fundamental to the determination of treatment and prognosis. MRI can be used to increase diagnostic certainty when a question exists concerning primary or metastatic marrow disease when other imaging studies are inconclusive. Chemical shift imaging may further improve the sensitivity and clinical utility of magnetic resonance imaging in patients with hematologic disorders involving the bone marrow.     

Magnetic resonance imaging of the bone marrow in hematological malignancies

Despite its lack of specificity, magnetic resonance imaging (MRI) of the bone marrow has the potential to play a role in the management of patients with primary neoplastic disorders of the hematopoietic system, including lymphomas, leukemias and multiple myeloma. In addition to its use in the assessment of suspected spinal cord compression, bone marrow MRI could be used as a prognostic method or as a technique to assess the response to treatment. The current review addresses the common patterns of bone marrow involvement observed in primary neoplasms of the bone marrow, basic technical principles of bone marrow MRI, and several applications of MRI in selected clinical situations. Received 22 May 1997; Revision received 27 January 1998; Accepted 29 January 1998     

Magnetic resonance imaging and magnetic resonance spectroscopy of bone tumors and bone marrow disease

The authors have made use of an integrated magnetic resonance imaging/spectroscopy (MRI/MRS) examination to study seven patients with a variety of bone tumors. The spatial localization method used in the 31P portion of the examination was surface coil localization and a one-dimensional chemical shift imaging method (3 cases). The authors found that the precision of spatial localization was critical in many of these cases, since most of these bone tumors were surrounded by muscle tissue that contained high concentrations of phosphocreatine (PCr). For this reason, they suggest that the metabolite ratios should be referenced to the adenosine triphosphate (beta-NTP) resonance rather than PCr. The phosphate monoester (PME) to beta-NTP ratio was elevated as compared with normal muscle in all of the bone tumors studied. The authors found that all of these tumors exhibited pHs between 7.0 and 7.2, which are similar to the values found for normal muscle. They also show the feasibility of using a line-selective proton chemical shift imaging sequence with high spatial resolution for investigating changes in the fatty composition of bone marrow. This method is illustrated in an example of a patient with advanced avascular necrosis in the femoral heads.     

Magnetic resonance imaging in diffuse malignant bone marrow diseases

Twenty-four patients with malignant bone marrow involvement or polycythemia vera, 8 patients with reactive bone marrow and 7 healthy individuals were examined with spin-echo magnetic resonance imaging at 0.35 T and 0.5 T. Signs of an increased longitudinal relaxation time, T1, were found when normal bone marrow was replaced by malignant cells, polycythemia vera or reactive marrow. A shortened T1 was indicated in 4 patients in bone marrow regions treated by radiation therapy; the marrow was most likely hypocellular in these cases. The estimated T1 relaxation times were highly correlated to the cellularity of the bone marrow as assessed by histology. Among patients with close to 100 per cent cellularity neither T1 nor T2 discriminated between the various malignancies or between malignant and reactive, non-malignant bone marrow. Characterization of tissues in terms of normalized image intensities was also attempted, the motive being to avoid approximations and uncertainties in the assessment of T1 and T2. The normalization was carried out with respect to the image of highest intensity, i.e. the proton density weighted image. The results were in agreement with those for T1 and T2. It was concluded that MRI is valuable for assessing bone marrow cellularity, but not for differentiating between various bone marrow disorders having a similar degree of cellularity.     

Magnetic susceptibility effects of trabecular bone on magnetic resonance imaging of bone marrow

High-field spectroscopic studies at 5.88 tesla (T) indicate significant T2* shortening of water in suspensions of powdered bone, interpreted to be a result of magnetic susceptibility differences between bone particles and water. The authors investigated the effects of magnetic susceptibility differences between trabecular bone and water on magnetic resonance (MR) images at 0.6 T. The phantom was constructed of macerated intact trabecular human bone immersed in water. Although susceptibility-induced magnetic field inhomogeneities were detected by spectral line broadening by using an asymmetric spin-echo technique, the results show only a modest T2* shortening at this field strength. As expected, no T1 effect of trabecular bone was observed. Although susceptibility effects of trabecular bone may have a small impact on the signal intensity of MR images of bone marrow at midfield strength, the observed field strength dependence of these effects would predict significant susceptibility effects on clinical images at higher field strength.     

Magnetic resonance imaging appearance of scurvy with gelatinous bone marrow transformation

Scurvy is a lethal but treatable disease that is rare in industrialized countries. Caused by vitamin C deficiency, it is most prevalent in persons of low socioeconomic status and smokers. Low levels of circulating vitamin C result in poor collagen fiber formation that, in turn, leads to demineralized bones, microfractures, and poor healing. Here we report a case of scurvy in a 5-year-old boy with normal radiographs in whom initial concern for leukemia based upon magnetic resonance imaging and clinical presentation led to a bone marrow biopsy revealing gelatinous transformation.     

Magnetic resonance imaging of bone marrow in oncology,Part 2

Magnetic resonance imaging plays an integral role in the detection and characterization of marrow lesions, planning for biopsy or surgery, and post-treatment follow-up. To evaluate findings in bone marrow on MR imaging, it is essential to understand the normal composition and distribution of bone marrow and the changes in marrow that occur with age, as well as the basis for the MR signals from marrow and the factors that affect those signals; these points have been reviewed and illustrated in part 1 of this two-part article. Part 2 will emphasize the practical application of MR imaging to facilitate differentiation of normal marrow, tumor, and treatment-related marrow changes in oncology patients, and will review complementary MR techniques under development. Part 1 of this article can be found at .     

Magnetic resonance imaging of bone marrow in oncology,Part 1

Magnetic resonance imaging plays an integral role in the detection and characterization of marrow lesions, planning for biopsy or surgery, and post-treatment follow-up. To evaluate findings in bone marrow on MR imaging, it is essential to understand the normal composition and distribution of bone marrow and the changes in marrow that occur with age, as well as the basis for the MR signals from marrow and the factors that affect those signals. The normal distribution of red and yellow marrow in the skeleton changes with age in a predictable sequence. Important factors that affect MR signals and allow detection of marrow lesions include alterations in fat–water distribution, destruction of bony trabeculae, and contrast enhancement. This two-part article reviews and illustrates these issues, with an emphasis on the practical application of MR imaging to facilitate differentiation of normal marrow, tumor, and treatment-related marrow changes in oncology patients. Part 2 of this article can be found at .     

Magnetic resonance investigation of bone marrow following priming and stem cell mobilization

PURPOSE: To evaluate application of MRI and magnetic resonance spectroscopy (MRS) to monitor bone marrow cellularity during pretransplant priming with chemotherapy and hematopoietic growth factor (HGF) administration. MATERIALS AND METHODS: A total of 10 lymphoma and myeloma patients, in remission following induction therapy and considered eligible for high-dose therapy and autologous stem cell transplantation, were included in the study. MR investigation was scheduled four times: at study entry, and one, two, and four weeks following priming. Priming with cyclophosphamide and recombinant human granulocyte colony-stimulating factor (rhG-CSF) started the day after study entry. MR parameters studied in a region of interest were as follows: bone marrow intensity on short-time inversion-recovery (STIR) turbo spin-echo (TSE; thus STIRTSE) and on T1-weighted TSE (T1TSE) images, T2 value for fat component, T2 value for water component, water/fat ratio (W/F), T1 value for fat component, and T1 value for water component. RESULTS: The results did not support the hypothesis that hematopoietic expansion quantitated and monitored by MR correlates to the level of mobilized progenitor cells. CONCLUSION: The results indicate that release of stem cells is a more complex phenomenon than hematopoietic expansion and reduction of fat tissue in bone marrow.     

Magnetic resonance imaging of disseminated bone marrow disease in patients treated for malignancy

Magnetic resonance imaging (MRI) is a sensitive method for the diagnosis of bone marrow abnormalities, but its usefulness in detecting active disseminated cancer in this tissue in treated patients has not been determined. We therefore examined 14 children who had been treated for disseminated bone marrow involvement by neuroblastoma (n=6), lymphoma (n=3), Ewing's sarcoma (n=3), osteosarcoma (n=1), and leukemia (n= 1). MRI studies were performed at 21 marrow sites to evaluate residual or recurrent tumor and were correlated with histologic material from the same site. T₁- and T₂-weighted sequences were employed in 21 and 14 studies, respectively; short tau inversion recovery (STIR) in 18; and static gadolinium diethylene triamine pentaacetic acid (Gd-DPTA)-enhanced, T₁-weighted sequences in 13. All MRI studies showed an altered bone marrow signal. Technetium 99m methylene diphosphonate (^99mTc-MDP) bone scintigraphy was also performed (19 studies). On histologic examination, 7 marrow specimens contained tumor, and 14 did not. Of the 7 tumor-positive lesions, all T₁-weighted, 4 of 6 T₂-weighted, and all 6 STIR sequences showed abnormal signal; all 5 GdDTPA-enhanced, T₁-weighted sequences showed enhancement of the lesion. However, abnormal signals were also observed on all T₁-weighted, 6 of 8 T₂-weighted, 11 of 12 STIR, and 5 of 8 Gd-DTPA-enhanced, T₁-weighted images of the tumor-negative sites. In this clinical setting, MRI did not consistently differentiate changes associated with treatment from malignant disease.     

Magnetic resonance tomography of the bone marrow for the detection of metastases of solid tumors]

The bone marrow is a common site of metastases in patients with solid tumors. Metastatic bone marrow involvement is found much more frequently at autopsy than in routine staging procedures. The purpose of this study was to evaluate the diagnostic efficacy of bone marrow MRI in such patients, and especially in those with small cell lung cancer and female breast carcinoma. MRI is a fast and reliable method for the early detection of bone marrow metastases in patients with carcinoma. In many studies and according to our own experience, it is much more sensitive than radionuclide bone scan, iliac crest biopsy and plain film radiography. However, a clear clinical benefit of its use in the initial staging has so far been proven only for patients with small cell lung cancer. As a consequence, MRI should be applied for the staging of solid tumors only when clinical examination does not yield unambiguous results. Owing to its superiority to biopsy and bone scan, bone marrow MRI should become an integral part of the initial staging procedure in small cell lung cancer and wherever it is sufficiently available it can replace the conventional diagnostic procedures.     

Magnetic resonance appearance of bone marrow edema associated with hydroxyapatite deposition disease without cortical erosion

The authors report the magnetic resonance (MR) appearance of bone marrow edema associated with hydroxyapatite deposition disease without cortical erosion. Hydroxyapatite deposition disease may have bone marrow edema on MR imaging without radiographic evidence of cortical erosion, mimicking the appearance of fracture, neoplasm, or infection. Awareness of this association can prevent unnecessary additional imaging evaluation or biopsy.     

Magnetic resonance imaging evaluation of bone marrow changes in obstructive sleep apnoea syndrome in adults

PURPOSE: The aim of this study was to evaluate bone marrow reconversion in patients with obstructive sleep apnoea syndrome (OSAS) by means of magnetic resonance imaging (MRI). To our knowledge, no explicit correlation between OSAS and such parameter has been documented in the literature. MATERIALS AND METHODS: During a 35-month period, 33 patients with a clinical diagnosis of OSAS, obese but without restrictive or obstructive ventilatory defects, were evaluated with MRI during wakefulness in all patients with T1-, PD- and T2-weighted sequences in the sagittal and axial plane within 1 week after polysomnography. RESULTS: MRI showed bone marrow reconversion in 33.3% of patients. Patients with bone marrow reconversion showed higher mean haematocrit (HT) values, lower mean nocturnal oxyhaemoglobin saturation, higher percentage of sleep time with oxygen saturation (SaO2) <90%, lower nadir, as well as greater neck adiposity and soft-palate lengthening compared with patients without bone marrow reconversion. Furthermore, in patients with bone marrow reconversion, haematocrit (HT) was negatively correlated with daytime arterial oxygen partial pressure (PaO2) and positively with arterial carbon dioxide partial pressure (PaCO2). CONCLUSIONS: In patients with OSAS, bone marrow reconversion is probably correlated with the severity of nocturnal desaturation. As bone marrow reconversion is, for unknown reasons, greater in adults younger than 40 years, MRI evidence of bone marrow reconversion could be useful in young individuals for the early diagnosis of sleep-disordered breathing and prevention of associated cardiovascular diseases.