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MRI future for early detection?


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A perfect picture

Kristine Novak

Despite the fact that magnetic resonance imaging (MRI) is a useful non-invasive means of identifying lymph nodes that contain large metastatic tumours, it cannot detect metastases at very early stages. Ralph Weissleder and colleagues have addressed this issue by using magnetic nanoparticles in conjuction with high-resolution MRI to find small, otherwise undetectable lymph-node metastases in patients with Prostate cancer.

Lymphotropic superparamagnetic nanoparticles have a superparamagnetic iron oxide core that can be detected by MRI, surrounded by a dense packing of dextrans that allow maintenance of the nanoparticles in the circulation. Weissleder and colleagues used MRI to show that, after injection, the particles circulate and accumulate in the lymph nodes. In normal lymph nodes, this signal eventually decreases as the particles are taken up by macrophages. In lymph nodes that contain metastases, however, there is either a limited decrease in signal intensity, or discrete focal defects within the node, due to replacement of nodal architecture by the tumour.

But how sensitive and accurate is this method of tumour detection? The authors analysed 334 lymph nodes taken from 80 patients with prostate cancer. As confirmed by surgical or biopsy analysis, standard MRI was only able to detect metastases in 45% of patients. MRI analysis of nanoparticle distribution, however, correctly identified all (100%) patients with nodal metastases. The technique also correctly identified 96% of patients that were metastasis-free.

Many of the metastases detected were less than 2 mm in diameter. This non-invasive technique is therefore a useful screening approach to identify patients that would not otherwise have been candidates for lymph-node surgery.

References and links


Harisinghani, M. G. et al. Noninvasive detection of clinically occult lymph-node metastases in prostate cancer. N. Engl. J. Med. 348, 2491-2499 (2003) | Article | PubMed |


Weissleder, R. Scaling down imaging: molecular mapping of cancer in mice. Nature Rev. Cancer 2, 11-18 (2002) | Article | PubMed | ChemPort |


Centre for Molecular Imaging Research, Massachusetts General Hospital

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