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Low-field interventional MRI in neurosurgery: finding the right dose of contrast medium
1Department of Neuroradiology, University of Heidelberg Medical School, Germany. Michael_Knauth@med.uni-heidelberg.de
Abstract:
MRI is increasingly being used as an interventional tool in neurosurgery. The field strength of "intraoperative" MR systems is usually lower than that of imagers commonly used for diagnostic purposes. However, lesion enhancement and apparent lesion extent depend on field strength. The aim of this study was to compare the contrast between intracranial, contrast-enhancing space-occupying lesions and the surrounding white matter obtained with low-field (0.2 T) and high-field (1.5 T) MR imaging and to find the contrast medium dosage for low-field MRI that produces the same lesion-to-white-matter contrast as the one obtained with high-field MRI after the administration of a standard dose of the contrast medium. A total of 38 patients with intracranial metastases or high-grade glioma were enrolled in this study. T1-weighted spin-echo sequences were acquired. High-field (1.5 T) studies were performed after the i.v. administration of 0.1 mmol gadolinium-DTPA/kg body weight. For low-field MRI (0.2 T) a dose escalation technique was used. T1-weighted sequences were repeated after each of three i. v. injections of 0.1 mmol gadolinium-DTPA/kg body weight. Thus, at the low-field examinations three T1-weighted sequences with a contrast medium dosage of 0.1, 0.2 and 0.3 mmol gadolinium-DTPA/kg body weight were obtained. Lesion-to-white-matter contrasts were calculated and compared. The average lesion-to-white-matter contrast obtained with high-field MR examinations was 1.63 (standard deviation 0.32). In the low-field MR examinations the average lesion-to-white-matter contrast was 1.34 (0.2) after a single dose, 1.57 (0.2) after a double dose, and 1.71 (.19) after a triple dose of contrast medium. The lesion-to-white-matter contrast of the high-field MR examination after a single dose of contrast medium was significantly higher than that of the low-field study after a single dose (P < 0.0001), but did not differ significantly from the low-field studies after a double (P = 0.28) or a triple dose (P = 0.17) of contrast medium. In a series of patients with contrast-enhancing space occupying brain lesions low-field MRI (0.2 T) after a double dose of contrast medium yielded the same lesion-to-white-matter contrasts as high-field MRI (1.5 T) after a standard dose. This is an important finding to avoid errors in intraoperative MRI due to the immanently lower degree of lesion enhancement in low-field MR imaging.
Insights
Low-field intraoperative MRI requires a double dose of contrast medium to achieve the same lesion enhancement as high-field MRI. This finding is crucial for accurate neurosurgical guidance using lower field strength magnetic resonance imaging (MRI) systems.
Area of Science:
- Neurosurgery
- Radiology
- Medical Imaging
Background:
- Intraoperative MRI (iMRI) is vital in neurosurgery.
- Lower field strength of iMRI systems can affect lesion visualization.
- Lesion enhancement and extent are field strength-dependent.
Purpose of the Study:
- Compare contrast between intracranial lesions and white matter at low-field (0.2 T) and high-field (1.5 T) MRI.
- Determine optimal contrast medium dosage for low-field MRI to match high-field contrast.
Main Methods:
- 38 patients with intracranial metastases or high-grade glioma studied.
- T1-weighted spin-echo sequences used for both field strengths.
- High-field: 0.1 mmol/kg gadolinium-DTPA (standard dose).
- Low-field: dose escalation (0.1, 0.2, 0.3 mmol/kg) to find equivalent contrast.
Main Results:
- High-field MRI (1.5 T) average contrast: 1.63.
- Low-field MRI (0.2 T) average contrast: 1.34 (single dose), 1.57 (double dose), 1.71 (triple dose).
- Low-field MRI with double contrast dose (1.57) matched high-field contrast (1.63) (P=0.28).
Conclusions:
- Low-field (0.2 T) MRI with a double dose of contrast medium achieves lesion-to-white-matter contrast comparable to high-field (1.5 T) MRI with a standard dose.
- This finding helps prevent diagnostic errors in intraoperative neuroimaging.
- Optimized contrast protocols are essential for low-field intraoperative MRI accuracy.