PET/CT Role in Diagnosis, Investigation, and Epidemiology of Common Diseases
PET/CT imaging has become a cornerstone of patient management in oncology, with established roles in diagnosis, staging, treatment response assessment, and detection of disease recurrence across various conditions that contribute to global morbidity and mortality. 1
Definition and Technical Aspects of PET/CT
PET/CT is an integrated imaging modality that combines:
- A Positron Emission Tomography (PET) scanner that detects metabolic activity using radiopharmaceuticals (most commonly [18F]FDG)
- A Computed Tomography (CT) scanner that provides anatomical information
- A single, joined patient handling system (table) that allows sequential acquisition with the patient in the same position 1
The integration of these two modalities provides co-registered functional and anatomical information, significantly improving diagnostic accuracy compared to either modality alone.
Common Imaging Protocols
PET/CT examinations can cover various imaging ranges:
- Whole-body imaging: From the top of the head through the feet
- Torso imaging: Base of the skull to mid-thigh (covers most relevant portions in many oncological diseases)
- Limited-area tumor imaging: For evaluation of tumor-related changes in a specific body region
- Dedicated brain imaging: Can be combined with whole-body or torso imaging 1
CT components may include:
- Low-dose CT: Performed only for attenuation correction and anatomical correlation
- Diagnostic CT: With or without contrast agents, using higher X-ray doses 1
Epidemiological Context and Common Indications
PET/CT has established roles in diagnosing and managing conditions that contribute significantly to global morbidity and mortality:
Oncology (Leading Cause of Global Mortality)
- Differentiation of benign from malignant lesions
- Searching for unknown primary tumors
- Staging known malignancies
- Monitoring treatment response
- Evaluating residual abnormalities post-treatment
- Detecting tumor recurrence
- Guiding biopsy and radiation therapy planning 1
The actual clinical use of PET/CT in oncology includes:
- Lung cancer (26% of PET/CT scans)
- Hematological malignancies (12%)
- Gastrointestinal cancers (9%)
- Head and neck cancers (4%)
- Skin cancers (4%)
- Gynecological cancers (8%) 1
Cardiovascular Disease
PET/CT is increasingly used in cardiovascular applications, potentially replacing myocardial scintigraphy in some settings 1. In prosthetic heart valve endocarditis, PET/CT has been incorporated into diagnostic criteria in the most recent ESC guidelines 1.
Infection and Inflammation
PET/CT has an increasingly relevant role in detecting:
- Septic emboli and metastatic infections
- Inflammation of unknown origin
- Fever of unknown origin 1
Investigation Lineup and Diagnostic Approach
The optimal diagnostic approach using PET/CT involves:
Pre-scan Assessment
Review of medical history:
- Diagnosis (type of cancer and known sites if applicable)
- Oncological history and relevant comorbidity
- Infection/inflammation and diabetes mellitus
- Recent medications (especially antidiabetics, corticosteroids, growth factors)
- Previous imaging results 1
Laboratory tests:
- Serum glucose (critical for FDG studies)
- Renal function (if contrast is planned)
- Relevant tumor markers 1
Patient Preparation
- Fasting for at least 4-6 hours
- Blood glucose control (particularly important in diabetic patients)
- Hydration and comfortable temperature to reduce brown fat uptake
- Minimizing muscle activity before and after tracer injection 1
Standardized Interpretation Criteria
For consistent reporting and interpretation, standardized criteria have been developed:
In oncology: The Deauville criteria (5-point scale) is commonly used for lymphoma assessment:
- DS 1 = No uptake
- DS 2 = ≤ mediastinal blood pool uptake
- DS 3 = > mediastinal blood pool uptake, ≤ liver uptake
- DS 4 = > liver uptake (at least 10% more)
- DS 5 = >> liver uptake (at least twice) 1
In plasma cell disorders: The IMPeTUs criteria evaluate:
- Metabolic state of bone marrow
- Number and site of focal lesions
- Presence of paramedullary disease
- Presence of extramedullary disease
- Presence of fractures on CT 1
In prosthetic valve endocarditis: PET/CT findings should be correlated with clinical and other diagnostic findings, ideally discussed in a multidisciplinary "Endocarditis Team" 1
Multidisciplinary Approach
The interpretation of PET/CT findings should be integrated with other clinical and diagnostic information. In complex cases like endocarditis, a multidisciplinary team approach is recommended, including:
- Cardiologists
- Cardiothoracic surgeons
- Microbiologists/infectious disease specialists
- Radiologists and nuclear medicine physicians 1
Pitfalls and Limitations
Important considerations to avoid misinterpretation:
False positives:
- Recent valve implantation (within 3 months)
- Inadequate suppression of myocardial FDG uptake
- Surgical adhesives
- Recent cytokine administration
- Inflammatory conditions 1
False negatives:
- Prolonged antibiotic therapy before imaging
- Small lesions (partial volume effect)
- Hyperglycemia affecting FDG uptake 1
Technical considerations:
- Standardized acquisition protocols are essential for quantitative assessment
- Consistent reconstruction methods are needed for comparison between scans 1
Future Perspectives
PET/CT applications continue to evolve:
- Therapy monitoring in immunotherapy
- Assessment of treatment response in plasma cell disorders
- Evaluation of antibiotic therapy effectiveness
- Integration with other advanced imaging modalities 1
The field is rapidly evolving, with increasing evidence supporting the cost-effectiveness of PET/CT in specific clinical scenarios, such as investigation of persistent/recurrent neutropenic fever in high-risk hematology patients 2.