Functional Imaging in Oncology

Functional Imaging in Oncology - Cancer's Inner Workings

Functional imaging visualizes and quantifies physiological or metabolic processes, offering insights beyond anatomical structure. It reveals tumor behavior.

• Key Processes Assessed:

  • Glucose metabolism (e.g., $^{\text{18}}\text{F-FDG}$ PET)
  • Cellular proliferation (e.g., $^{\text{18}}\text{F-FLT}$ PET)
  • Tumor hypoxia (e.g., $^{\text{18}}\text{F-FMISO}$ PET)
  • Angiogenesis (e.g., DCE-MRI, specific PET tracers)
  • Receptor expression (e.g., $^{\text{68}}\text{Ga-DOTATATE}$ for SSTRs)

• Advantages in Oncology:

  • Early detection & characterization
  • Accurate staging, restaging, prognostication
  • Early treatment response assessment
  • Guiding therapies & biopsies

vs tumor structure (anatomical imaging))

⭐ PET-CT, fusing PET's metabolic data with CT's anatomy, is key for staging, restaging, and monitoring therapy response in many cancers.

PET/CT in Oncology - Sweet Tumor Trackers

• Principle: PET (metabolic activity via positron emitters) + CT (anatomical map) = Fused functional-structural imaging for precise tumor assessment.
• 18F-FDG (Fluorodeoxyglucose):
  • Mechanism: Glucose analog; GLUT uptake, hexokinase phosphorylation $ ightarrow$ $^18F-FDG-6-P$; trapped in high-glucose-use cells (cancer, inflammation).
  • Physiological Uptake: Brain, myocardium, liver, kidneys, bladder, bowel, marrow, brown fat (BAT). 📌 "Brain Loves Sugar, So Do Tumors!"
  • Pitfalls: Inflammation, infection, muscle activity, BAT, recent interventions.
• SUV (Standardized Uptake Value):
  • Semi-quantitative measure of tracer uptake in Region of Interest (ROI).
  • Concept: $SUV = \frac{\text{ROI Activity Conc. (MBq/mL)}}{\text{Injected Dose (MBq) / Body Weight (kg)}}$.
  • Factors: Blood glucose, uptake time, patient size, reconstruction.
  • Utility: Lesion characterization, staging, therapy response (e.g., PERCIST).
• Key Non-FDG PET Tracers:

  Tracer	Target	Key Indication(s)
  Ga-68 DOTATATE	SSTR	Neuroendocrine Tumors
  Ga-68 PSMA	PSMA	Prostate Ca
  18F-FLT	TK1 (Prolif.)	Proliferation
  18F-FMISO	Hypoxia marker	Hypoxia

• Applications: Diagnosis (limited), staging, restaging, recurrence detection, monitoring therapy response (PERCIST).

⭐ FDG-PET/CT detects viable tumor in post-therapy residual masses when CT is equivocal, guiding treatment decisions.

Functional MRI in Oncology - Magnetic Moves & Maps

⭐ A significantly low Apparent Diffusion Coefficient (ADC) value on DWI is a strong indicator of high tumor cellularity and is often associated with aggressive tumor behavior.

SPECT, Response & Future - More Tools, New Rules

• SPECT: Functional imaging (metabolic/physiologic data).
  • Bone Scintigraphy: $^{99m}$Tc-MDP for osteoblastic metastases.
  • SLN Mapping: Pre-op radiotracer localization.
• Tumor Response:
  • RECIST 1.1: Anatomical (size changes).
  • PERCIST: Metabolic (PET SUV changes).

  ⭐ PERCIST assesses metabolic response for early treatment efficacy, unlike size-based RECIST.

• Theranostics: "See it, treat it." E.g., $^{177}$Lu-DOTATATE (NETs), $^{177}$Lu-PSMA (Prostate Ca).
• Future: Radiomics, AI in image analysis.

High‑Yield Points - ⚡ Biggest Takeaways

• FDG-PET/CT is key for staging, restaging, and response assessment in many cancers.
• SUVmax quantifies metabolic activity; has limitations and is not an absolute measure.
• Specific tracers like PSMA-PET (prostate cancer) & DOTATATE-PET (neuroendocrine tumors) improve diagnostic specificity.
• DWI MRI reflects tumor cellularity, aiding in detection and treatment response assessment.
• DCE MRI evaluates tumor vascularity and permeability, crucial for anti-angiogenic therapy monitoring.
• Functional imaging often detects tumor recurrence earlier than anatomical imaging alone.
• Hypoxia imaging (e.g., FMISO-PET) can identify radioresistant tumor regions, guiding therapy.