IVIM method is a diffusion-weighted MRI sequence used to estimate perfusion parameters, which has several advantages over commonly used methods. It is a non-invasive alternative to perfusion measurement, eliminating the need for intravenous injection of exogenous contrast agent through a single image sequence, reducing examination time. In addition, its signal is highly spatially specific because it comes primarily from a place where measurements are taken independently of the arterial blood flow path before reaching there. Finally, it provides additional information compared to ASL, and the combination of the two approaches can be used for the assessment of neurological diseases[17].
It recently reported that the IVIM parameters could help to more precisely assess the early diagnosis and differentiation of diseases, as well as quantitatively monitor the effectiveness of treatment for tumors and other diseases. Ding Y etl.[18] compare the diagnostic values of IVIM, conventional DWI, and diffusion kurtosis imaging (DKI) in differentiating between benign and malignant renal tumors. They found the D value is the best parameter for differentiating cell renal cell carcinoma (ccRCC) from benign renal tumors. The f value is the best parameter for differentiating non-ccRCC from benign renal tumors. IVIM parameters are the best, while DWI and DKI parameters have similar performance in differentiating malignant and benign renal tumors. Another article found that rectal cancers with different KRAS mutation statuses had distinctive diffusion/perfusion characteristics. D values were lower in the KRAS mutant group. A higher D* value was demonstrated in the KRAS mutant group. IVIM MRI may potentially help preoperative KRAS mutant status prediction[19]. Zhu L etl. [20] evaluated the performance of tumor size and IVIM-derived parameters in predicting long-term prognosis, found that IVIM MR imaging has great potential in predicting long-term prognosis in patients with advanced cervical cancers treated with concurrent chemo-radiotherapy.
In early or atypical spinal tuberculosis, there is no typical obvious bone erosion or abscess, and the imaging findings are complex and sometimes similar to tumors, leading to misdiagnosis. While this is not common, it is still necessary to find ways to avoid it. Within the spinal column, metastasis is more commonly found in the thoracic region, followed by the lumbar region, while the cervical region is the least likely place professionals find metastasis. The aim of this study is to evaluate the performance diagnostic values of IVIM MRI for differentiating spinal metastasis. To the best of our knowledge, our investigation is the first to illustrate the IVIM relative parameters for differentiation of spinal tuberculosis and spinal metastasis.
Our results shown that some IVIM parameters could help discriminate spinal metastasis from tuberculous spondylitis and could investigate the feasibility of tumor type differential diagnosis of different metastases, including lung cancer, breast cancer and renal cancer. Conventional DWI is based on the micro-movement of water molecules, which reflects the speed of water diffusion in the tissue. ADC values can quantitatively evaluate tissue diffusion and show microscopic changes at the cellular level caused by pathophysiological changes. In our study, no significant difference in ADC values was found between spinal metastases and tuberculous spondylitis, suggesting an ADC overlap in distinguishing them. Therefore, the results show that the role of traditional ADC DWI in differentiating benign and malignant lesions of the spine is limited, which is consistent with previous studies[4, 21–22] .
It is known that the ADCslow is mainly affected by water molecule diffusion of the lesion tissue and ADCfast is mainly affected by capillary microcirculation perfusion. Our results showed the ADCfast value of spinal metastases was significantly higher than that of tuberculous spondylitis, which suggests that perfusion greatly increases. However, no significant differences were found between the ADCslow values between them. But the ADCslow value of spinal metastasis with lung cancer was significantly lower than that of spinal metastasis with breast cancer as well as with renal cancer, suggesting that true diffusion is more restricted in lung cancer than breast cancer and renal cancer. ADCfast and f values except for ADCslow value showed better diagnostic performance than ADC value for differentiating spinal metastasis and tuberculous spondylitis. The f value is mainly affected by the blood volume of microcirculation perfusion, reflecting the proportion of microcirculation perfusion in tissue diffusion. Our results showed that f value of spinal metastasis was lower than that of tuberculous spondylitis group. Similar findings have been found in nasopharyngeal, pancreatic, and cervical lymph node metastases in previous studies[23–24]. The reasons might be the high cell density of spinal metastasis, the microvessels in the intercellular stroma were compressed, and the new vessels in malignant lesions were compressed, deformed and branched disorderly, leading to the decrease of the proportion of microperfusion components. In our study, ADCfast combined with f showed much higher AUC than ADCfast and f. these finding suggested that ADCfast combined with f was more valuable for the differential diagnosis of spinal metastasis and tuberculous spondylitis.
The DDC and α value reflects the heterogeneity of diffusion in the tissue. The value of α is set between 0 and 1. The closer the α value is to 1, the higher the homogeneity of the diffusion component is; the closer the α value is to 0, the higher the heterogeneity of the diffusion component is and the more complex the diffusion component is. In this study, the DDC and α value of spinal metastasis was lower than that of tuberculous spondylitis. however, there was no significant. indicating that compared with tuberculous spondylitis, malignant tissue is more complex and heterogeneous, which leads to the decrease of DDC and α value. Additional significant differences were found in the ADCstand, ADCslow, DDC and α among different metastasis type. The reasons for the above results may be related to the pathophysiological changes of the disease and the theory behind different imaging techniques.
Although with novel findings, our study also has some limitations, which we would further improve in the future work. Firstly, the small sample size of spinal metastasis and tuberculous spondylitis. Secondly, All values were measured by manual outlining ROI, and the ROI was placed on the solid components of the tumor to calculate the average value. Although it was representative to some extent, it was not conducive to the evaluation of tumor heterogeneity. Thirdly, IVIM technology itself is not stable. So far there is no specific standard about multiple b value of IVIM sequences, and the calculations still need further exploration[25].
In conclusion, IVIM MR imaging may be helpful for differentiating spinal metastasis from tuberculous spondylitis and provide help for clinical treatment. The combined ADCfast and f parameters are better than ADCfast, and f. Despite the small patient population, this study may lead to further developments in the application of IVIM in differentiating benign and malignant spinal skeletal lesions.