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Amide proton transfer (APT) imaging is an emerging molecular MRI technique based on chemical exchange saturation transfer where the imaging contrast is generated by endogenous mobile proteins and peptides. Previous studies have shown that APT signal increases with increasing malignancy grade of gliomas, hypothetically reflecting abundant cytosolic protein due to high cellularity. Cavernous malformation is rare, highly vascular benign lesion that has very low cellularity. Here, we report a cavernous malformation that showed markedly high APT signal.A 70-year-old woman presented with left facial discomfort and progressive loss of vision in the left eye for 6 months. Magnetic resonance imaging was performed using a 3T scanner (Ingenia 3.0T; Philips Healthcare, Best, The Netherlands) equipped with dual-source parallel radiofrequency transmission system and a 15-channel head coil for signal reception, which revealed a left cavernous sinus mass with hypointensity on T 1 -weighted imaging, marked hyperintensity on T 2 -weighted imaging, and strong homogenous enhancement after contrast injection (Fig. 1).Amide proton transfer imaging based on two-dimensional single slice single-shot turbo spin-echo technique was performed: TR, 4550 ms; TE, 4.8 ms; flip angle 90ç; turbo factor 128; number of signal averaging, 1; FOV, 230 × 230 mm 2 ; imaging matrix, 128 × 128 (reconstructed in 256 × 256); slice thickness, 5 mm. A quasi-continuous saturation pulse with an amplitude of 2 μT and a duration of 2 s (40 × 50 ms, sin c-Gaussian elements) was applied at 27 offset frequencies including 24 ranging from +6 to −6 ppm with a step of 0.5 ppm and 2 at ±9.6 ppm as well as one far off-resonance frequency (−1560 ppm) for signal normalization. During postprocessing, the B 0 field inhomogeneity was corrected on a voxel-by-voxel basis using a separately obtained map of B 0 . The APT images were obtained by calculating the magnetization transfer ratio asymmetry (MTR asym ) between ±3.5 ppm using the B 0 -corrected MT-spectrum: MTR asym (3.5 ppm) = (S −3.5 ppm -S 3.5 ppm ) /S 0 × 100 (%), where S ±3.5 ppm and S 0 represent signal intensities at ±3.5 ppm and −1560 ppm, respectively. The intratumoral APT signal (MTR asym at 3.5 Vppm) was 6.9%, which is substantially higher than that in the contralateral normal-appearing tissue (0.8%) (Fig. 2) and also, par or even higher than the values previously reported for glioblastomas (typically, 4-5%). The mass was partially resected. Histopathological examination revealed a cavernous malformation.We speculate that the high APT signal in the cavernous malformation is attributable to the blood filling multiple dilated vascular channels in the lesion, which contains various

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Background and Purpose: Differentiation between hemangioblastoma and brain metastasis remains a challenge in neuroradiology using conventional MRI. Amide proton transfer (APT) imaging can provide unique molecular information. This study aimed to evaluate the usefulness of APT imaging in differentiating hemangioblastomas from brain metastases and compare APT imaging with diffusion-weighted imaging and dynamic susceptibility contrast perfusion-weighted imaging.Methods: This retrospective study included 11 patients with hemangioblastoma and 20 patients with brain metastases. Region-of-interest analyses were employed to obtain the mean, minimum, and maximum values of APT signal intensity, apparent diffusion coefficient (ADC), and relative cerebral blood volume (rCBV), and these indices were compared between hemangioblastomas and brain metastases using the unpaired t-test and Mann-Whitney U test. Their diagnostic performances were evaluated using receiver operating characteristic (ROC) analysis and area under the ROC curve (AUC). AUCs were compared using DeLong's method.Results: All MRI-derived indices were significantly higher in hemangioblastoma than in brain metastasis. ROC analysis revealed the best performance with APT-related indices (AUC = 1.000), although pairwise comparisons showed no significant difference between the mean ADC and mean rCBV.Conclusions: APT imaging is a useful and robust imaging tool for differentiating hemangioblastoma from metastasis.

Amide proton transfer (APT) imaging is a magnetic resonance (MR) molecular imaging technique that is sensitive to mobile proteins and peptides in living tissue. Studies have shown that APT-related signal intensity (APTSI) parallels with the malignancy grade of gliomas, allowing the preoperative assessment of tumor grades. An increased APTSI in malignant gliomas has been attributed to cytosolic proteins and peptides in proliferating tumor cells; however, the exact underlying mechanism is poorly understood. To get an insight into the mechanism of high APTSI in malignant gliomas, we investigated the correlations between APTSI and several MR imaging parameters including apparent diffusion coefficient (ADC), relative cerebral blood volume and pharmacokinetic parameters obtained in the same regions-of-interest in 22 high-grade gliomas. We found a significant positive correlation between APTSI and ADC (ρ = 0.625 and 0.490 for observers 1 and 2, respectively; p < 0.001 for both), which is known to be inversely correlated with cell density. Multiple regression analysis revealed that ADC was significantly associated with APTSI (p < 0.001 for both observers). Our results suggest possible roles of extracellular proteins and peptides in high APTSI in malignant gliomas.