Purpose of review This review aims to cover current MRI techniques for assessing treatment response in brain tumors, with a focus on radio-induced lesions. Recent findings Pseudoprogression and radionecrosis are common radiological entities after brain tumor irradiation and are difficult to distinguish from real progression, with major consequences on daily patient care. To date, shortcomings of conventional MRI have been largely recognized but morphological sequences are still used in official response assessment criteria. Several complementary advanced techniques have been proposed but none of them have been validated, hampering their clinical use. Among advanced MRI, brain perfusion measures increase diagnostic accuracy, especially when added with spectroscopy and susceptibility-weighted imaging. However, lack of reproducibility, because of several hard-to-control variables, is still a major limitation for their standardization in routine protocols. Amide Proton Transfer is an emerging molecular imaging technique that promises to offer new metrics by indirectly quantifying intracellular mobile proteins and peptide concentration. Preliminary studies suggest that this noncontrast sequence may add key biomarkers in tumor evaluation, especially in posttherapeutic settings. Summary Benefits and pitfalls of conventional and advanced imaging on posttreatment assessment are discussed and the potential added value of APT in this clinicoradiological evolving scenario is introduced.
Purpose Accurate glioma classification affects patient management and is challenging on non- or low-enhancing gliomas. This study investigated the clinical value of different chemical exchange saturation transfer (CEST) metrics for glioma classification and assessed the diagnostic effect of the presence of abundant fluid in glioma subpopulations. Methods Forty-five treatment-naïve glioma patients with known isocitrate dehydrogenase (IDH) mutation and 1p/19q codeletion status received CEST MRI (B1rms = 2μT, Tsat = 3.5 s) at 3 T. Magnetization transfer ratio asymmetry and CEST metrics (amides: offset range 3–4 ppm, amines: 1.5–2.5 ppm, amide/amine ratio) were calculated with two models: ‘asymmetry-based’ (AB) and ‘fluid-suppressed’ (FS). The presence of T2/FLAIR mismatch was noted. Results IDH-wild type had higher amide/amine ratio than IDH-mutant_1p/19qcodel (p < 0.022). Amide/amine ratio and amine levels differentiated IDH-wild type from IDH-mutant (p < 0.0045) and from IDH-mutant_1p/19qret (p < 0.021). IDH-mutant_1p/19qret had higher amides and amines than IDH-mutant_1p/19qcodel (p < 0.035). IDH-mutant_1p/19qret with AB/FS mismatch had higher amines than IDH-mutant_1p/19qret without AB/FS mismatch ( < 0.016). In IDH-mutant_1p/19qret, the presence of AB/FS mismatch was closely related to the presence of T2/FLAIR mismatch (p = 0.014). Conclusions CEST-derived biomarkers for amides, amines, and their ratio can help with histomolecular staging in gliomas without intense contrast enhancement. T2/FLAIR mismatch is reflected in the presence of AB/FS CEST mismatch. The AB/FS CEST mismatch identifies glioma subgroups that may have prognostic and clinical relevance.
Distinguishing tumor recurrence from radionecrotic injury of pre-irradiated brain metastases is fundamental to provide optimal patient care. Unfortunately, this distinction is often hard to make even with advanced MRI multimodal protocols. This study aims to evaluate APTw imaging in predicting the differentiation between radio-induced tissue changes from tumor progression at 3T in 20 pre-irradiated metastases. Results show that APTw metrics can significantly separate these two common radiological entities (p<0.0001) and suggest the use of fluid-suppressed APTw to reach higher discriminating values.
PurposeAccurate gliomas classification affects patient management and is challenging on non- or low-enhancing gliomas. This study investigated the clinical value of different Chemical Exchange Saturation Transfer (CEST) metrics for glioma classification and assessed the diagnostic effect of the presence of abundant fluid in gliomas subpopulations.MethodsForty-five treatment-naïve glioma patients with known isocitrate dehydrogenase (IDH) mutation and 1p/19q codeletion status received CEST MRI at 3T. Magnetisation transfer ratio asymmetry and CEST metrics (amides: offset range 3-4ppm, amines: 1.5-2.5ppm, amides/amines ratio) were calculated with two models: ‘asymmetry-based’ (AB) and ‘fluid-suppressed’ (FS). Presence of T2/FLAIR mismatch was noted.ResultsIDH-wildtype had higher amides/amines ratio than IDH-mutant_1p/19qcodel (p<0.022). Amides/amines ratio and amines levels differentiated IDH-wildtype from IDH-mutant (p<0.0045) and from IDH-mutant_1p/19qret (p<0.021). IDH-mutant_1p/19qret had higher amides and amines than IDH-mutant_1p/19qcodel (p<0.035). IDH-mutant_1p/19qret with AB/FS mismatch had higher amines than IDH-mutant_1p/19qret without AB/FS mismatch (p<0.016). In IDH-mutant_1p/19qret, the presence of AB/FS mismatch was closely related to the presence of T2/FLAIR mismatch (p=0.014).ConclusionsCEST-derived biomarkers for amides, amines and their ratio can help with histomolecular staging in gliomas without intense contrast enhancement. T2/FLAIR mismatch is reflected in the presence of AB/FS CEST mismatch. The AB/FS CEST mismatch identifies glioma sub-groups that may have prognostic and clinical relevance.
This novel study explores amide proton transfer weighted (APTw) imaging in people with relapsing-remitting multiple sclerosis (pw-RRMS). We evaluated the APTw signal intensity in selected MS lesions and normal-appearing white matter (NAMW) regions in 9 pw-RRMS. Compared to NAWM regions, a statistically significant increase in APTw signal intensity was observed in the MS lesions. Elevated APTw signal intensity could mark increased mobile myelin proteins decomposition and accumulation from the demyelination process.
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