Which type of MRI to find prostate cancer bone metastases? Diffusion-weighted MRI

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Jim Marshall (not a doctor) said ...

MRI (Magnetic Resonance Imaging) makes pictures of the inside of your body that are better than x-rays for seeing some things.

MRI has three components:

• A magnet (very much stronger than the one that sticks to your fridge door)
  
• Radio waves (much better tuned than the ones your cordless phone uses)
  
• Optional injected contrast agents affected by magnets (manganese is one)
  

By pulsing the magnet and the radio in different patterns, and changing the contrast agent, MRIs can be used to emphasize different types of tissues.

Diffusion-weighted MRI best shows how water molecules are spread through the tissue.

Short-tau inversion recovery (STIR) MRI can see better through fat.

The article below tells that finding prostate cancer bone metastases is much better with diffusion-weighted MRI.

MRI scans are expensive. I have been quoted between $500 and $900 per scan.

In Australia at the time of writing (2 September 2012) they are not covered for this use in public hospitals of by private health insurance.

The stronger the magnets in an MRI machine, the finer the detail, and the more expensive they are. Current machines are mostly 1.5 Tesla and 3 Tesla. Top currently are the 17 Tesla machines

... end Jim

Br J Radiol. 2012 Aug;85(1016):1102-6. Epub 2012 Mar 28.

Bone metastases from prostate, breast and multiple myeloma: differences in lesion conspicuity at short-tau inversion recovery and diffusion-weighted MRI.

Pearce T, Philip S, Brown J, Koh DM, Burn PR.

Source

Department of Diagnostic Imaging, Musgrove Park Hospital, Taunton, UK.

Abstract

Objectives:

The objective of this study was to compare the relative conspicuity of bone metastases on short-tau inversion recovery (STIR) and diffusion-weighted MRI (DWI) whole-body MR sequences for breast, prostate and myeloma malignancies.

Methods:

44 whole-body MRI scans were reviewed retrospectively (coronal T(1) weighted, STIR and DWI with b=800). On each scan, up to four of the largest bone lesions were identified on T(1) weighting, and the region of interest signal intensity was measured on STIR and DWI, as well as the background signal intensity. The mean lesion signal to background ratio was calculated for each patient and then for each malignancy group.

Results:

In prostate cancer patients, the DWI signal/background ratio was greater than that of STIR in 22 out of 24 patients (mean DWI lesion/background ratio 3.91, mean STIR lesion/background ratio 2.31; p=0.0001). In multiple myeloma, the DWI ratio was higher in 6/7 patients (DWI group mean ratio 7.59, STIR group mean ratio 3.7; p=0.0366). In 13 breast cancer patients, mean STIR and DWI signal/background were similar (DWI group mean ratio 4.13, group mean STIR ratio 4.26; p=0.8587).

Conclusion:

Bone lesion conspicuity measured by lesion/background signal intensity was higher on DWI b=800 than on STIR in patients with prostate cancer and multiple myeloma. DWI should be used in whole-body MR oncology protocols in these conditions to maximise lesion detection.

PMID: 22457319

This extract can be found on http://PubMed.com, and is in the public domain.

On PubMed.com there will be a link to the full paper (often $30, sometimes free).

Any highlighting (except the title) is not by the author, but by Jim Marshall.

Jim is not a doctor.