T₁ snapshot flash measurement of rat brain glioma: kinetics of the tumor‐enhancing contrast agent manganese (iii) tetraphenylporphine sulfonate

Abstract

The ultrafast inversion recovery snapshot FLASH technique was used to determine the kinetics of the contrast agent manganese (III) tetraphenylporphine sulfonate (MnTPPS) in experimental brain tumors in rats. In the first part of the investigation this technique was validated with the conventional inversion recovery spin-echo method by comparing in vivo T1 data of a normal rat brain. Agreement between T1 values obtained from both techniques was complete, as tested for a large number of pixels in identical coronal slices. In the second part the fast IR snapshot FLASH method was applied to study the effect of the NMR contrast agent MnTPPS on the T1 relaxation time of experimental gliomas in rat brains. T1 of normal brain tissue (1024-1035 ms), tumor (1217 ms), and edema (1199 ms) was determined with the inversion recovery version of the snapshot FLASH imaging technique. After intraperitoneal injection of MnTPPS (0.25 mmol/kg body wt) T1 decreased exponentially to 56% of control in tumor and to 62% in muscle. In normal and edematous brain tissue no significant changes in T1 were observed up to 5 h after injection of the contrast agent. Once the T1 contrast between tumor and peritumoral brain tissue had reached a saturation, the enhancement persisted for several hours to days. Therefore application of this contrast agent resulted in a sharp demarcation between glioma and peri-tumoral edema.

Identification of intracranial liqor metastases of experimental stereotactically implanted brain tumors by the tumor-selective MRI contrast agent MnTPPS

“…Previous MRI studies in experimental brain tumors have shown that metallated porphyrins such as MnTPPS can be used for selectively increasing the signal intensity in neoplastic tissue and, in consequence, for enhancing the contrast between tumoral and normal tissue [10,11,13,14]. In contrast to barrier tracers such as Gd-DTPA [2], which have found widespread clinical use, porphyrin derivatives accumulate in neoplastic tissue [8,9].…”

“…The signal enhancement in the tumor remained constant from day 1 to day 4 after MnTPPS application (Wilmes et al, in preparation) [13]. In a separate study we had observed the change of T1 relaxation time in the rat brain glioma during the first 5 h after MnTPPS application [14], clearly showing that the steadystate contrast situation is reached within less than 2 h. As the cat was tracheotomized, no long-term study with repeated anesthesia was possible. Therefore the MRI scans were continued for up to 24 h after application of MnTPPS.…”

“…Therefore the MRI scans were continued for up to 24 h after application of MnTPPS. This was found to be sufficient as the steady-state situation of the contrast enhancement was reached within approximately 2 h [11], in analogy to the situation in the rat [14].…”

Rapid monitoring of oxygenation by 19F magnetic resonance imaging: Simultaneous comparison with fluorescence quenching

“…Finally, the mouse was sacrificed using 5% isoflurane in air for 20 min. Parametric images of the spin-lattice relaxation time (T 1 ) were estimated using a snapshot inversion recovery (SNAP-IR) pulse sequence (13)(14)(15). The pulse sequence consisted of a nonselective hyperbolic secant inversion pulse (10 ms length), followed by acquisition of a series of 512 rapid gradient echo images (repetition time ϭ 10.9 ms, echo time ϭ 4.2 ms, flip angle ϭ 1°, matrix ϭ 32 ϫ 16, field of view ϭ 60 ϫ 30 mm, bandwidth ϭ 12.5 kHz, single thick slice [projection], total acquisition time ϭ 1.5 min) (Fig.…”

“…Raw (k-space) data were zero-filled to a matrix size of 64 ϫ 64, resulting in interpolated 64 ϫ 64 images. For each image pixel T 1 was estimated by fitting the standard 3-parameter monoexponential recovery equation (magnitude data only) describing the signal as a function of inversion time (13)(14)(15). We denote this computed T 1 as T 1 Ј because the recovery curve is somewhat perturbed by the RF pulses (16).…”