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Comparison of reduced field-of-view DWI and conventional DWI in the assessment of lumbar bone marrow infiltration in patients with acute leukemia1Shanxi Medical University, Taiyuan, China, 2The Second Hospital of Shanxi Medical University, Taiyuan, China
Synopsis
Keywords: Quantitative Imaging, Diffusion/other diffusion imaging techniques, Reduced field-of-view, Acute leukemia, Image quality, Cellularity
Motivation: To investigate whether reduced field-of-view diffusion-weight imaging (r-FOV DWI) is superior to conventional DWI for the evaluation of bone marrow infiltration in acute leukemia (AL).
Goal(s): To compare the imaging quality, apparent diffusion coefficient, and value of assessing bone marrow infiltration between r-FOV DWI and conventional DWI in the lumbar spine of AL.
Approach: The image quality and the performance in assessing bone marrow infiltration of the two sequences in AL were compared qualitatively and quantitatively.
Results: Compared with conventional DWI, r-FOV DWI provides superior image quality of the lumbar spine in AL patients, thus yielding better performance in assessing bone marrow infiltration.
Impact: The findings suggest that r-FOV DWI is a promising technique for reducing image artifacts, improving image quality, and assessing bone marrow infiltration in AL. r-FOV DWI can be proposed as a common sequence for evaluating bone marrow infiltration in AL.
Introduction
Acute leukemia (AL) is a malignant clonal disease of hematopoietic stem cells. Increased bone marrow cellularity in AL would inhibit the Brownian motion of water molecules, which could be quantitatively reflected by the apparent diffusion coefficient (ADC) value obtained from diffusion‑weighted imaging (DWI)1,2. Single-shot echo-planar imaging (SS-EPI) technique is most commonly used for DWI. However, it is susceptible to main field inhomogeneities, local gradients, as well as chemical shift effects due to its long readout time and low sampling bandwidth in the phase-encode direction3-5. Anatomical features unique to the spine also pose technical challenges4-6. Although optimized DWI scanning protocols have developed to address these issues, the use of these methods were restricted due to complex principle, penalties in acquisition time and higher demand of MRI equipment in hardware and software4-6. In recent years, reduced field-of-view (r-FOV) DWI, has been proposed to improve the spatial resolution, minimize image distortion, and diminish artifacts. We hypothesized that r-FOV DWI could augment evaluation of lumbar bone marrow in AL by improving image quality. Therefore, the aims of the present study were to compare the imaging quality of r-FOV DWI with conventional DWI in the lumbar spine of AL patients, and to evaluate whether the ADC value obtained with r-FOV DWI has better performance for assessing bone marrow infiltration in AL.Methods
Patients with newly diagnosed AL were recruited and underwent both r-FOV DWI and conventional DWI in the lumbar spine. Two radiologists evaluated image quality scores using 5-Likert-type scales qualitatively and measured signal-to-noise ratio (SNR), contrast-to-noise (CNR), signal intensity ratio (SIR), and ADC quantitatively. Patients were divided into hypo- and normocellular group, moderately hypercellular group, and severely hypercellular group according to bone marrow cellularity (BMC) obtained from bone marrow biopsies. The image quality parameters and ADC value between r-FOV DWI and conventional DWI were compared by Wilcoxon signed-rank test or paired t-test. One-way analysis of variance followed by LSD post hoc test was used for the comparisons of the ADC values among the three groups. The performance of ADC obtained from r-FOV DWI (ADCr) and conventional DWI(ADCc) in evaluating BMC and their correlations with BMC and white blood cell counts were analyzed and compared.Results
71 AL patients (hypo- and normocellular: n=20; moderately hypercellular: n=19; severely hypercellular: n=32) were evaluated. The image quality scores (all p<0.001), CNR (2.66 ± 1.96 vs 2.46 ± 1.85, p=0.034), SIR (1.42 ± 0.64 vs 1.21 ± 0.50, p<0.001), and ADC value (0.76 ± 0.25 ×10-3 mm2/sec vs 0.31 × ± 0.12 ×10-3 mm2/sec, p< 0.001) of r-FOV DWI were significantly higher than those of conventional DWI, and the SNR of r-FOV DWI was significantly lower (25.81 ± 16.48 vs 45.02 ± 22.07, p<0.001). ADCr showed statistically significant differences in all pairwise comparisons among the three groups (0.926±0.238 vs 0.772±0.223 vs 0.617±0.164, all p<0.05), while ADCc showed significant difference only between hypo- and normocellular group and severely hypercellular group (0.356±0.126 vs 0.282±0.077, p=0.014). The performance of ADCr in evaluating BMC (Z=2.380, p=0.017) and its correlations with BMC (Z=-2.022, p = 0.043) and white blood cell counts (Z=-2.008, p = 0.045) were significantly higher than those of ADCc.Discussion
Our results suggested the overall image quality was improved on r-FOV DWI with sharper anatomical structure, reduced distortions and artifacts, and higher CNR as well as SIR when compared with conventional DWI. By reducing the FOV in the phase-encoding direction, r-FOV DWI has a faster traverse of k-space and a higher bandwidth, which enables it to achieve a higher spatial resolution in the same scan time and decrease image artifacts such as blurring and pixel misregistration7-9. Imaging distortions could be reduced by decreasing the number of acquisition steps and shortening the length of the EPI echo train on r-FOV DWI with a spatially selective RF pulse7.In our study, ADCr can distinguish three groups of cellularity with different degrees, while ADCc was only able to distinguish the hypo- and normocellular group and the severely hypercellularity group. Furthermore, ADCr demonstrated better diagnostic efficacy than ADCc in differentiating between the hypo- and normocellular group and the severely hypercellular group. Although ADC values from both conventional DWI and r-FOV DWI were negatively correlated with BMC and WBC counts, ADCr showed significantly higher correlations than ADCc. Accordingly, r-FOV DWI could be a superior alternative to conventional DWI in evaluating bone marrow infiltration of AL.
Conclusion
Compared with conventional DWI, r-FOV DWI provides superior image quality of the lumbar spine in AL patients, thus yielding better performance in assessing bone marrow infiltration.Acknowledgements
No acknowledgement found.References
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Figures
Figure 3. Receiver operating characteristic curves of the diagnostic performance of ADC values for differentiating among hypo- and normocellular group, moderately hypercellular group, and severely hypercellular group. In the differentiation between the hypo- and normocellular group and the severely hypercellular group, ADCr demonstrated better diagnostic performance than ADCc.
