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Superparamagnetic iron oxide: enhanced detection of focal splenic tumors with MR imaging
R Weissleder1, P F Hahn, D D Stark
1Department of Radiology, Massachusetts General Hospital, Boston 02114.
Abstract:
Superparamagnetic iron oxide (AMI-25), a reticuloendothelial cell-specific contrast agent for magnetic resonance (MR) imaging, was evaluated for its ability to permit detection of splenic metastases in 18 patients. Superparamagnetic iron oxide, at a dose of 30 mumol of iron per kilogram, decreased the signal intensity of spleen from 19.5 +/- 4.8 to 3.1 +/- 2.2 (spin-echo sequence, repetition time msec/echo time msec = 1,500/42; P less than .05), without changing the signal intensity of tumor. As a result, the tumor-spleen contrast-to-noise ratio increased from 0.2 (tumor isointense relative to spleen) to 18.0 (tumor hyperintense relative to spleen). As a consequence of increased contrast, splenic tumors were detected in four of 18 patients (45 individual lesions; P less than .05), whereas nonenhanced MR imaging permitted detection of splenic lesions in only two of 18 patients (four individual lesions). Maximum tumor-spleen contrast was achieved within 60 minutes after intravenous administration. These initial clinical results indicate that MR imaging with superparamagnetic iron oxide may offer improved accuracy in the diagnosis of splenic tumors.
Insights
Superparamagnetic iron oxide (AMI-25) enhances magnetic resonance (MR) imaging for spleen. This contrast agent improved detection of splenic tumors, increasing diagnostic accuracy for metastases.
Area of Science:
- Radiology
- Oncology
- Medical Imaging
Background:
- Spleen metastases are challenging to detect with conventional MR imaging.
- Reticuloendothelial cell-specific contrast agents offer potential for improved lesion visualization.
Purpose of the Study:
- To evaluate the efficacy of superparamagnetic iron oxide (AMI-25) for detecting splenic metastases using MR imaging.
- To assess the impact of AMI-25 on spleen signal intensity and tumor-to-spleen contrast.
Main Methods:
- 18 patients with suspected splenic metastases underwent MR imaging.
- AMI-25 was administered intravenously at a dose of 30 µmol of iron per kilogram.
- Signal intensity changes in the spleen and tumors were measured using spin-echo sequences.
Main Results:
- AMI-25 significantly decreased spleen signal intensity (P < .05).
- Tumor signal intensity remained unchanged, leading to a substantial increase in tumor-spleen contrast-to-noise ratio (from 0.2 to 18.0).
- Splenic tumors were detected in 4/18 patients (45 lesions) with AMI-25 enhanced MR, compared to 2/18 patients (4 lesions) without enhancement.
Conclusions:
- MR imaging with superparamagnetic iron oxide (AMI-25) significantly improves the detection of splenic tumors.
- AMI-25 enhances tumor-spleen contrast, offering a promising tool for diagnosing splenic metastases.
- Optimal contrast enhancement was observed within 60 minutes post-administration.