Klinische Magnetresonanztomographie mit reduzierter Energie (B1+rms ≤ 2 μT) zur Untersuchung von Patienten mit aktiven Implantaten
OBJECTIVES: Radio frequency (RF) pulses in magnetic resonance imaging (MRI) can interact with implanted devices and cause tissue damage. However, there are new devices that can safely perform measurements with liberal MRI conditions such as an RF transmission field B1+rms ≤ 2.0 µT. We investigated whether MRI in this case is limited for these technical reasons. METHODS: We selected typical MRI protocols of six body regions (brain, cervical spine, lumbar spine, knee, liver, heart) using two typical 1.5T MRI scanners. Overall, we adapted 62 sequences to B1+rms conditions and evaluated their diagnostic quality. For this we measured signal-to-noise-ratio (SNR), contrast-to-noise-ratio (CNR) and geometric deviation (GD) as quality parameters, using phantom studies. For questionnaire studies, we selected pairs of original and adapted sequences in healthy volunteers. Blinded radiologists rated the images as single sequence rating and in direct comparison. RESULTS: Roughly one third of the checked sequences was below the B1+rms limit. Here, 56 of 62 adapted sequences showed at least the same image quality in single ratings. A reduction in SNR and/or CNR was found with 31 sequences and only one sequence with considerably increased GD. Especially, sequences with original high B1+rms values, PD-sequences and sequences of the Siemens knee and heart protocol were difficult to adapt, whereas most TSE- and IR-sequences had no clinical limitations. CONCLUSION: By limiting the transmission field to B1+rms ≤ 2.0 μT clinically relevant MR sequences can be adapted with nearly no reduction in image quality. Despite limiting the transmission field, high quality MR imaging is possible. We could derive strategies for adaptation.
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