Departments of 1 Radiology and 2 Clinical Therapeutics, Medical School, University of Athens, Athens; 3 Department of Medical Physics, University Hospital of Heraklion, Heraklion, Crete; 4 Department of Radiology, General Hospital of Chios, Chios, Greece
Received 21 March 2002; revised 5 June 2002; accepted 17 July 2002
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Abstract |
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The purpose of this study was to evaluate the role of dynamic contrast-enhanced magnetic resonance imaging (dMRI) in detecting bone marrow involvement in cancer patients.
Patients and methods:
We studied 50 consecutive patients with histologically confirmed malignant dissemination to the bone marrow, using dMRI of the lumbosacral spine. Timesignal intensity curves were generated from regions of interest (ROIs) obtained from areas of obvious bone marrow disease (group B). In 16 patients from group B with focal disease, ROIs were also placed on areas with apparently normal bone marrow on static magnetic resonance images (group C). Twenty-two patients with no history of malignancy were used as a control group (group A). Wash-in (WIN) and wash-out (WOUT) rates, time to peak (TTPK), time to maximum slope (TMSP) values and WIN/TMSP ratios were calculated for each patient. Mean values for the three groups were compared statistically. Six patients from group B had follow-up dMRI after chemotherapy: four patients achieved a clinical partial response and two had resistant disease.
Results:
A significant difference was found between groups A and B for all values. Between groups A and C, in spite of the similar static MRI appearance, all values were significantly different. Between groups B and C, a significant difference was found for WIN, WOUT rates and WIN/TMSP ratio. Follow-up dMRI data analysis correlated well with clinical staging.
Conclusions:
dMRI can distinguish normal from malignant bone marrow. It may identify malignant bone marrow infiltration in patients with negative static MRI and serve as both a diagnostic and prognostic tool for patients with bone marrow malignancies.
Key words: bone marrow, dynamic magnetic resonance imaging, magnetic resonance imaging
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Introduction |
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The absence of a single predictable pattern of red to yellow marrow conversion in the spine complicates the search for malignant bone marrow lesions further [3]. The institution of chemotherapy and, in particular, the concomitant use of growth factors leads to an increase in the volume of red marrow. In addition to red marrow hyperplasia, other disorders of the bone marrow that can complicate the course of disease in a cancer patient (fibrosis, infarction, edema related to recent compression fractures, infection) may also simulate tumor.
Dynamic contrast-enhanced magnetic resonance imaging (dMRI) studies the kinetics of the distribution of paramagnetic contrast in the microvessels and in the interstitial space of the tissues being studied. dMRI has been applied to the study of musculoskeletal tumors, with encouraging results regarding the diagnosis of malignant from benign and viable from non-viable tumor, and the prediction and assessment of response to chemotherapy [49]. We undertook this study to investigate the potential of dMRI to separate malignant bone marrow disease from uninvolved bone marrow, and its ability to detect underlying disease in patients with known bone marrow malignancies and normal conventional MRI studies.
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Materials and methods |
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Six patients (one patient each with breast cancer, lung cancer, cervical cancer and myelodysplastic syndrome, and two with multiple myeloma) had follow-up dMRI studies within a month from completion of therapy.
Oral consent was obtained from all patients.
MR imaging
Magnetic resonance images were obtained with a 1.5 T unit (Philips Medical Systems, Eindhoven, The Netherlands). Sequences for static MRI included sagital T1-weighted SE [repetition time (TR) = 500600 ms, echo time (TE) = 1020 ms] and turbo short-time inversion recovery [STIR; TR = 1620 ms, inversion time (TI) = 180 ms, TE = 70 ms, turbo spin echo factor = 12) images of the lumbosacral spine. Imaging parameters were: 4 mm section thickness, 1 mm interslice gap, 204 x 256 imaging matrix, 23 signals averaged. dMRI was performed with a T1-weighted gradient-echo sequence (TR = 11 ms, TE = 4.2 ms, flip angle = 30°). The dynamic study was limited to a single spinal part to avoid inherent variations in perfusion between different spinal locations. The lumbosacral spine was selected for dMRI over other skeletal parts to match the patients studies with those of the control group.
Five sections through the spine, carefully selected from the static study to encompass areas of abnormal marrow, were obtained every 18 s for a total of a maximum of 3 min. A bolus of gadopentetate dimeglumine 0.1 mmol/kg body weight (Magnevist; Schering, Berlin, Germany) was injected manually immediately after the end of the first dynamic acquisition.
After completion of the MRI study, all contrast-enhanced dynamic images were subtracted from the first set of unenhanced images by using the subtraction function of the magnetic resonance (MR) unit. For each normal control of group A, a region of interest (ROI) was positioned on one of the lumbar vertebral bodies, avoiding the areas affected by motion artifacts. For each patient of group B, subtraction images were reviewed and an ROI was placed on a focus of maximum abnormal enhancement. Foci of abnormal enhancement that could be related to vertebral endplate perfusion changes that accompany degenerative disc disease were excluded from the study. All ROIs measured between 70 and 80 pixels, and were carefully selected to avoid the basivertebral vessels that course at the midline of each vertebra. ROIs were selected on a single image and were then plotted automatically on all images of the same dynamic series. In 16 patients from group B in whom the neoplastic process did not appear to involve the entire bone marrow on the static MR images, a second ROI was positioned at a site of apparently normal marrow (group C). For the six patients from group B who had follow-up dMRI studies, ROIs were positioned on the same vertebra as during the pre-treatment study.
Data analysis
The dynamic signal enhancement (DSE) of selected ROIs was plotted as a function of time (t) and signal intensitytime curves were generated (Figures 1, 2 and 3). Signal intensitytime data obtained from each ROI were fitted by means of a Marquardt linear regression analysis method [10] according to the formula:
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Parameters (a, b, c, d) were calculated from the fit of DSE to t.
For all fits, r was 0.9. This value was used as a threshold for the estimation of goodness of each fit. Wash-in (WIN) and wash-out (WOUT) rates were calculated for each patient from the maximum and minimum slopes of signal intensitytime curves, respectively. These slopes, as well as time to peak (TTPK) and time to maximum slope (TMSP) values were obtained from the first derivative function f(t) = d(DSE)/dt of equation (1). The ratio WIN/TMSP was also calculated.
Patients and normal controls were divided into three sample groups for statistical evaluation of the results: (i) group A (normal controls); (ii) group B (patients with abnormal bone marrow); and (iii) group C (patients from group B with areas of normal-appearing bone marrow on static MR images). Assuming the possibility of difference in standard deviations amongst compared populations, an unpaired t-test with Welch correction was used to check statistical significance amongst all groups (sample means) using WIN, WOUT, TTPK, TMSP values and the ratio of WIN/TMSP. A P value of 0.05 was considered a statistically significant threshold.
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Results |
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Abnormal compared with normal-appearing bone marrow (groups B and C). Mean WIN and WOUT rates and WIN/TMSP ratios were significantly higher for the group with abnormal bone marrow (group B) compared with those of the group with apparently normal bone marrow on static MR images (group C).
Mean TTPK and TMSP values for groups B and C did not differ significantly.
Normal compared with normal-appearing bone marrow (groups A and C). Mean WIN rates and WIN/TMSP ratios were significantly shorter for group A compared with those of group C.
Mean TTPK and TMSP values were significantly higher for group A when compared with group B.
Follow-up MRI
Four of six patients with malignant bone marrow disease who had follow-up MRI achieved a clinical partial response to treatment, while in two patients the disease progressed.
dMRI diagnosis was consistent with the clinical evaluation in all patients (Tables 4 and 5; Figure 4).
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Discussion |
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Dynamic contrast-enhanced MRI has been applied extensively to the study of solid musculoskeletal tumors, but there are very few publications on dMRI of bone marrow. Bollow et al. studied 30 patients with B-cell-type chronic lymphocytic leukemia (B-CLL) and 45 patients without known malignancy with dMRI of the bone marrow, and found significant differences between patients with Binet stages B and C of B-CLL and normal controls [11]. Hawighorst et al. reported differences in pharmacokinetics between 10 patients with multiple myeloma and seven healthy controls who were studied with dMRI of the bone marrow [12]. Both studies show that there are significant differences between the contrast profiles of normal bone marrow and those of hematopoietic malignancies.
Our study showed significant differences between signal intensitytime curves obtained from normal controls (group A) and those obtained from patients with malignant disease of the bone marrow (group B). When compared with red marrow, enhancement of abnormal bone marrow occurred earlier, was steeper and did not last as long. All four parameters, calculated from the fit of the dynamic signal enhancement to time, differed significantly between the two groups (Table 3). The higher WIN and WOUT, and the lower TTPK and TMSP values of malignant bone marrow compared with those of normal bone marrow in our study reflect the faster throughput of contrast material, which can be explained by the presence and number of abnormal vessels with increased size and permeability [13].
Before a malignant bone marrow lesion becomes apparent on a conventional MRI study, it must replace enough normal bone marrow cells to cause a local alteration of T1 and T2 values; in cases of early dissemination to the bone marrow, a conventional MRI study may indeed be normal. Because an abnormal dMRI signal intensitytime curve depends on contrast medium kinetics, it may detect tumor neovascularity before a lesion becomes apparent on conventional MRI. In our study, signal intensitytime curves obtained from areas of bone marrow that did not appear to be involved on pre-contrast MR images of patients with known malignant dissemination to the bone marrow (apparently normal bone marrow; group C) were clearly different from those obtained from healthy controls (group A); quantitative analysis confirmed this observation by showing significant differences in all four parameters calculated from the fit of the dynamic signal enhancement to time, and in the WIN/TMSP ratio, which reflects the speed of change of WIN values (Table 3).
When apparently normal bone marrow signal intensitytime curves (group C) were compared with those of abnormal bone marrow (malignant bone marrow; group B), a significant difference was found only between WIN and WOUT values and WIN/TMSP ratios. However, TTPK and TMSP values of apparently normal bone marrow approximated those of malignant bone marrow. Dynamic MRI profiles of apparently normal bone marrow (group C) bared a closer resemblance to those of abnormal bone marrow (group B) than to those obtained from healthy controls. Whether the difference in contrast kinetics is due to the presence of neovascularity related to tumor angiogenesis or whether it could be related to increased perfusion of uninvolved bone marrow that is located adjacent to a site of tumoral infiltration remains to be seen. Hawighorst and colleagues reported significantly higher contrast uptake in patients with monoclonal gammopathy of unknown significance (MGUS) compared with normal controls, even though a distinction between the two groups based on visual interpretation of the conventional MRI study was not possible [12]. It seems, therefore, that dMRI of the bone marrow may show changes during the early phase of tumor angiogenesis and, thus, diagnose bone marrow involvement before it becomes apparent on conventional MR images. Correlation of dMRI data with histopathological parameters related to tumor angiogenesis may confirm the above hypothesis.
If dMRI can distinguish red marrow from abnormal marrow, one of its potential applications is the detection of residual disease in patients who are being treated for malignant disease of the bone marrow. In all six patients who had follow-up dMRIs in our study, dMRI data were in accordance with the clinical evaluation of response (Tables 4 and 5). Conversely, conventional post-treatment MR images failed to show any change from the baseline study in four out of six patients. In one patient with myelodysplastic syndrome, dMRI correctly diagnosed response to treatment in spite of the absence of abnormal findings in both pre- and post-treatment conventional MRI studies. It is possible that dMRI may detect the presence or absence of changes indicative of response to treatment before these become evident on the static MR images, providing, therefore, the attending physician with an early assessment of treatment.
Clearly, our data applies only to the differential diagnosis of malignant from uninvolved red marrow, and further studies comparing signal intensitytime curves of malignant bone marrow infiltration with those of benign bone marrow abnormalities or endplate abnormalities associated with degenerative disc disease may be relevant. The latter were carefully avoided in our study because increased bone marrow perfusion related to their presence could alter the contrast uptake profile of uninvolved, normal bone marrow. However, most of the benign disorders that may complicate the course of treatment in a cancer patient have morphological characteristics that should enable their diagnosis on pre-contrast MR images.
Dynamic MRI is easily performed and the software is available in most currently used MR units. We have shown that dMRI can distinguish normal from abnormal bone marrow. Mapping of normal bone marrow contrast profiles in different age groups, and dMRI studies of patients with the same bone marrow malignancy and correlation of dMRI data with parameters of the histopathologic specimen may not only establish the role of dMRI in the work-up of bone marrow malignancies, but may also provide information on the development and evolution of bone marrow malignancies from the early phase of angiogenesis.
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Footnotes |
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References |
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