Synopsis

To increase the MR value of spinal imaging in patients with suspected or known malignant disease, we propose the use of sagittal diffusion weighted imaging as replacement for traditional image types such as STIR and T2W TSE. The impact of this protocol is threefold. Scan times are reduced from potentially 50 minutes to 15 minutes for the whole spine; making scans more tolerable for patients with back pain, reducing cost and increasing scanner capacity. Reader confidence is increased in detecting malignant infiltration especially when diffuse. Finally, read times are reduced as there are fewer images to review.

Clinical Question

Impact

In patients with metastatic malignancy, spinal imaging may be used for diagnosis, monitoring or assessment of complications such as fractures or cord compression. Often, patients are imaged using a combination of modalities including X-rays, CT, MRI, bone scans and PET, although if there are symptoms of cord compression MRI is usually the imaging modality of choice. MRI is also used in patients with known spinal tumours to monitor response to treatment. The diagnosis of diffuse tumour infiltration can be problematic. Where there is a disease that infiltrates the entire bone marrow (such as leukaemia or advanced metastatic tumours present, for example, as may occur in Ewing’s sarcoma), the homogeneity of the marrow can mislead non-expert reporters and diffuse tumour infiltration can be missed.

Impact of revised protocol

1. Reduced scan time is of economic benefit, increases scanner capacity and is better tolerated by patients with back pain.

2. Improving confidence for diagnosing malignancy is of clinical benefit and potentially of economic benefit by reducing the use of ancillary imaging (eg PET scans).

3. Reducing scan read time is of economic benefit and increases reader capacity.

1. Approach

1. Gains and Losses

The gains of this approach are that acquisition time is shorter and reading time is decreased due to fewer images to review. Acquisition time for the new approach is approximately 15 minutes for the whole spine compared to 40 minutes (50 minutes with contrast) for the old approach. T1W sagittal images have been shown to be non-inferior to T2W sagittal images in detecting cord compression and superior for detecting fractures ^3,4. Therefore in terms of diagnostic information we expect non-inferiority compared to the traditional approach. DWI may be more specific for tumour and tumour response than STIR imaging ⁵, and diffuse malignant disease should be more easily detectable on DWI than conventional imaging.

The main losses of this approach are the lack of axial images and the potential for missing malignant pathology through the use of fewer sequences. However the new approach does not preclude the use of additional sequences on a case-by-case basis if the new 2-sequence protocol is not sufficient. We hypothesise that malignant lesions are at least as conspicuous on DWI as STIR. It is foreseeable that benign cause of back pain in these patients may not be apparent on the new approach such as disc protrusions.

1. Preliminary Data

Our preliminary retrospective data are derived from an experimental protocol including all the above mentioned traditional sequences with the addition of sagittal diffusion sequence on 10 patients with known malignancies including multiple myeloma, gastric, breast and rectal cancer. Representative areas of malignant infiltration are highlighted by arrows on the DWI image. The diagnostic information gleaned from the high value protocol was equivalent to the old protocol. Diffuse infiltration was better demonstrated by DWI compared to STIR (Figure 4). The T1W images were sufficient as an anatomical sequence compared to T2W images.

We predict that a whole spine protocol consisting of sagittal DWI and unenhanced sagittal T1W spin echo would take approximately 15 minutes compared to the traditional approach and thus reduce costs per patient, and increase patient throughput. Cost effectiveness would also be increased shorter scan reading times. Furthermore a shorter scan time will improve patient experience especially those with severe back pain.

Acknowledgements

References

1. Wang B, Fintelmann FJ, Kamath RS, Kattapuram S V, Rosenthal DI. Limited magnetic resonance imaging of the lumbar spine has high sensitivity for detection of acute fractures, infection, and malignancy. Skeletal Radiol. 2016

2. Shah LM, Salzman KL. Imaging of spinal metastatic disease. Int J Surg Oncol. 2011;2011:769753

3. Johnson AJ, Ying J, El Gammal T, Timmerman RD, Kim RY, Littenberg B. Which MR imaging sequences are necessary in determining the need for radiation therapy for cord compression? A prospective study. AJNR Am J Neuroradiol. 2007;28(1):32–37

4. Kim JK, Learch TJ, Colletti PM, Lee JW, Tran SD, Terk MR. Diagnosis of vertebral metastasis, epidural metastasis, and malignant spinal cord compression: are T(1)-weighted sagittal images sufficient? Magn Reson Imaging. 2000;18(7):819–824

5. Lecouvet FE, Larbi A, Pasoglou V, et al. MRI for response assessment in metastatic bone disease. Eur Radiol. 2013;23(7):1986–1997