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. 2025 Dec 8:58:e20250060.
doi: 10.1590/0100-3984.2025.0060. eCollection 2025 Jan-Dec.

State of the art of PET/MRI for rectal cancer: the added value to conventional imaging

Poliana Fonseca Zampieri  1 , Daniel Barros Garcia Hernandes  1 , David Alberto Gutiérrez Albenda  1 , Natally Horvat  2 , Onofrio Antonio Catalano  3 , Carlos Alberto Buchpiguel  1 , Marcelo Araújo Queiroz  1
Affiliations

State of the art of PET/MRI for rectal cancer: the added value to conventional imaging

Poliana Fonseca Zampieri et al. Radiol Bras. .

Abstract
in English, Portuguese

Imaging plays a critical role in the assessment of patients with rectal cancer, and positron emission tomography/magnetic resonance imaging (PET/MRI) has shown superiority in specific clinical scenarios. This review describes the potential contribution of 18F-fluorodeoxyglucose (18F-FDG) PET/MRI relative to standard of care imaging-computed tomography (CT), MRI, or PET/CT-in the evaluation of patients with rectal cancer in settings such as primary staging, treatment response assessment, and recurrence detection. We discuss 18F-FDG PET/MRI protocols and clinical workflow, as well as highlighting the potential clinical superiority of PET/MRI over other imaging modalities.

Os exames de imagem desempenham um papel fundamental na avaliação de pacientes com câncer retal, e a tomografia por emissão de pósitrons/ressonância magnética (PET/RM) tem demonstrado superioridade em cenários clínicos específicos. Esta revisão descreve a potencial contribuição da PET/RM com 18F-fluorodesoxiglicose (18F-FDG) em relação à imagem padrão - tomografia computadorizada (TC), RM ou PET/TC - na avaliação de pacientes com câncer retal em cenários como estadiamento primário, avaliação da resposta terapêutica e detecção de recidiva. Discutimos os protocolos e o fluxo de trabalho clínico da PET/RM com 18F-FDG, além de destacar a potencial superioridade clínica da PET/RM sobre outras modalidades de imagem.

Keywords: Magnetic resonance imaging; Positron-emission tomography; Rectal neoplasms.

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Figures

Figure 1
Figure 1
Clinical workflow in 18F-FDG PET/MRI for rectal cancer staging.
Figure 2
Figure 2
A 56-year-old male at primary staging of rectal cancer. The primary tumor and its extensions are better seen in the MRI component (A). DWI (B) aids in the detection of viable tumors but is not strictly necessary in primary staging. The PET component (C) shows a very high 18F-FDG uptake, and PET parameters can be quantified, helping identify high-risk patients .
Figure 3
Figure 3
A 56-year-old male at primary staging of rectal cancer. A: MRI detects a lesion with an extensive mucinous component (red arrow) and some nonmucinous components (yellow arrow). B: PET/MRI clearly shows the difference between the mucinous and nonmucinous components by highlighting 18F-FDG avidity.
Figure 4
Figure 4
A 48-year-old female at primary staging (A) and treatment response assessment following neoadjuvant CRT (B). PET/MRI after neoadjuvant CRT showed a partial metabolic response with residual 18F-FDG uptake suggestive of a viable tumor. The patient underwent surgery that confirmed the staging as ypT3ypN0.
Figure 5
Figure 5
A 57-year-old male at primary staging (A) and treatment response assessment following neoadjuvant CRT (B). At primary staging, PET/MRI detected a hypermetabolic primary rectal tumor staged as T3N0 (A). PET/MRI after neoadjuvant CRT showed a complete metabolic response, although a partial morphology response (tumor regression grade 3) was depicted by MRI (B).
Figure 6
Figure 6
Restaging in a 57-year-old male with rectal cancer and rising CEA levels. PET/CT (B) depicts 18F-FDG uptake without a clear morphological change on CT (A). However, local recurrence was detected on MRI (C) and PET/MRI (D).
Figure 7
Figure 7
Clinical impact of PET/MRI on primary staging of rectal cancer (A), treatment response assessment (B), and detection of recurrence (C). nCRT, neoadjuvant CRT; RT, radiotherapy; mrTRG, magnetic resonance tumor regression grade.
See this image and copyright information in PMC

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