Investig Magn Reson Imaging.  2017 Jun;21(2):65-70. 10.13104/imri.2017.21.2.65.

Depiction of Acute Stroke Using 3-Tesla Clinical Amide Proton Transfer Imaging: Saturation Time Optimization Using an in vivo Rat Stroke Model, and a Preliminary Study in Human

Affiliations
  • 1Department of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea. dynamics79@gmail.com
  • 2Philips Research, Hamburg, Germany.
  • 3Philips Healthcare Korea, Philips House, Seoul, Korea.

Abstract

PURPOSE
To optimize the saturation time and maximizing the pH-weighted difference between the normal and ischemic brain regions, on 3-tesla amide proton transfer (APT) imaging using an in vivo rat model.
MATERIALS AND METHODS
Three male Wistar rats underwent middle cerebral artery occlusion, and were examined in a 3-tesla magnetic resonance imaging (MRI) scanner. APT imaging acquisition was performed with 3-dimensional turbo spin-echo imaging, using a 32-channel head coil and 2-channel parallel radiofrequency transmission. An off-resonance radiofrequency pulse was applied with a Sinc-Gauss pulse at a B(1,rms) amplitude of 1.2 µT using a 2-channel parallel transmission. Saturation times of 3, 4, or 5 s were tested. The APT effect was quantified using the magnetization-transfer-ratio asymmetry at 3.5 ppm with respect to the water resonance (APT-weighted signal), and compared with the normal and ischemic regions. The result was then applied to an acute stroke patient to evaluate feasibility.
RESULTS
Visual detection of ischemic regions was achieved with the 3-, 4-, and 5-s protocols. Among the different saturation times at 1.2 µT power, 4 s showed the maximum difference between the ischemic and normal regions (-0.95%, P = 0.029). The APTw signal difference for 3 and 5 s was -0.9% and -0.7%, respectively. The 4-s saturation time protocol also successfully depicted the pH-weighted differences in an acute stroke patient.
CONCLUSION
For 3-tesla turbo spin-echo APT imaging, the maximal pH-weighted difference achieved when using the 1.2 µT power, was with the 4 s saturation time. This protocol will be helpful to depict pH-weighted difference in stroke patients in clinical settings.

Keyword

Amide proton transfer; Stroke; pH-difference; Saturation time

MeSH Terms

Animals
Brain
Head
Humans*
Infarction, Middle Cerebral Artery
Magnetic Resonance Imaging
Male
Models, Animal
Protons*
Rats*
Rats, Wistar
Stroke*
Water
Protons
Water

Figure

  • Fig. 1. Characterization of acute middle cerebral artery occlusion using amide proton transfer imaging. (a) 3 seconds, (b) 4 seconds, (c) 5 seconds protocol. The 4 s protocol showed maximal visual contrast and localization of the ischemic region.

  • Fig. 2. Diffusion-weighted imaging and TTC (triphenyltetrazolium hydrochloride) stain for the same Wistar rat shown in Figure 1, shows the ischemic region matched with amide proton transfer imaging.

  • Fig. 3. Amide proton transfer (APT) imaging with a 4 s saturation time protocol applied to a 69-year-old male, 4 days after an acute middle cerebral artery occlusion (a). (b) The diffusion-restriction region matched the reduced APT-weighted signal region, compared to the contralateral normal appearing brain.


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