Magnetization transfer effects on T1-weighted three-dimensional gradient-echo MR images of a phantom simulating enhancing brain lesions.
OBJECTIVE
To develop a simple tissue phantom to study the effects of various imaging parameters and gadolinium concentrations on magnetization transfer (MT) and lesion-to-background ratios.


METHODS
A commercial egg product was doped with gadolinium in concentrations of 0.0 to 1.0 mmol/L and cooked. The T1 and T2 values were determined for the phantom materials and for the white and gray matter of a healthy volunteer subject. The gadolinium-doped egg phantom and human brain were studied using a short-repetition-time three-dimensional gradient-echo MT sequence with various effective MT powers, frequency offsets, and section-select flip angles. The normalized signal intensities, MT ratios (MTRs), and simulated lesion-to-background normal white matter contrast ratios were determined for a variety of experimental conditions.


RESULTS
The MTR and lesion-to-background contrast ratios for all materials were greatest at the highest effective MT power (270 Hz, root-mean-square of amplitude) and the narrowest MT pulse frequency offset (1000 Hz). There was an inverse relationship between gadolinium concentration and MTR, and a positive relationship between the gadolinium concentration and lesion-to-background contrast. MTR was greatest at low flip angles, where there was little T1 weighting. The simulated lesion-to-background contrast showed a complex, gadolinium concentration-dependent relationship with section excitation flip angle.


CONCLUSIONS
The tissue phantom has relaxation properties and MT behavior close to that expected for enhancing brain lesions, allowing a rigorous analysis of simulated lesion-to-background contrast for high MT power, short-repetition-time, three-dimensional gradient-echo sequences.
Finelli
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Department of Radiology, MetroHealth Medical Center, Case Western University, School of Medicine, Cleveland, Ohio 44109, USA.
D001921:Brain / Q000473:pathology; D001932:Brain Neoplasms / Q000175:diagnosis*; D003287:Contrast Media; D005583:Fourier Analysis; D019786:Gadolinium DTPA; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D009942:Organometallic Compounds; D004369:Pentetic Acid / Q000031:analogs & derivatives; D019047:Phantoms, Imaging; D012016:Reference Values
D003287:Contrast Media; D009942:Organometallic Compounds; D004369:Pentetic Acid; C064925:gadodiamide; D019786:Gadolinium DTPA