Chapter 1: The science and the scan

"Boring, But Necessary"

1. What is a PET/CT Scan?

Hybrid Imaging System
Anatomic & Functional Exam
The Machine
“Whole Body” vs. “Skull Base to Mid-Thigh”
Three Sets of Images
Produced

2. Basic Science 18F-FDG

Glucose Analog
Malignancy & Glucose Metabolism
Mechanisms for Increased Intracellular Glucose
Why 18F-FDG Works

3. Power of PET/CT

Whole Body Assessment
The “You’re Kidding Me!” Effect
Post-Therapeutic Scar vs. Active Malignancy

4. Indications for PET/CT

Detecting Malignancy
Staging Malignancy
Assess Response to Therapy
Detecting Recurrence

5. The Limitations of PET/CT

Not All Cancer is FDG-Avid
Normal FDG-Uptake vs. Pathologic Uptake
Technical Limitations
- Poor Patient Preparation
- Misregistration
- Brown Fat Activation
- SUV Problems
- Fields of View Discrepancy
- PET/CT Artifacts
- Timing of Exam After Therapy

6. Images Generated

CT Images
Non-Attenuation Corrected Images
Attenuation Corrected Images
Maximum Intensity Projection (MIP)
Fusion of Images
All Images Viewed in 3 Planes

7. Contrast Media: Oral & I.V.

Who Gets Oral Contrast?
Who Gets IV Contrast?
Oral Contrast “Cocktail” Recipe

8. What the Patient Should Expect

Documenting Height & Weight
Private Resting Room
Drinking PO Contrast
FDG Injection
Delay Between Injection & Scan

9. Safety Concerns with PET/CT Imaging

Radiation Exposure to Patient
Radiation Exposure to Patient’s Contacts
Patient Contact with Pregnant Women
Breastfeeding

Chapter 2: PET/CT Problems Which Limit Interpretation

"Something just doesn't seem right here"

1. Poor Patient Preparation

Optimizing Glucose & Insulin Levels
- Fasting Prior to Exam
- Diabetic Patients
- Low Carbohydrate Diet
- Hydration
Strenuous Exercise
Voiding Prior to Exam
Patient Instruction Sheet

2. Brown Fat

Definition
Distribution / Appearance
Don’t Miss the Hidden Nod
Reporting Language
Prevention

3. Timing of PET/CT Exam After Therapy

“Rule of 3”
- Chemotherapy: 1 month
- Surgery: 2 months
- Radiation: 3 months

4. Misregistration

Etiology: Hybrid Imaging
Patient Movement
Respiratory Motion
Breathing Techniques
Bowel Peristalsis

5. Extravasation of FDG

False Positives
False Negatives
Reporting Language

6. PET/CT Artifacts

Beam Hardening
Diaphragmatic Mismatch
Linear Hand Motion
Attenuation Correction
Differing Fields of View

7. The “Sponge Effect”

Poor Patient Preparation
FDG Extravasation
Extensive Brown Fat
Metformin-Induced Bowel Uptake
Marked Reactive Marrow Uptake
Extensive Tumor Uptake in

8. SUV Complications

Different Types of SUV Measurements
Factors that Influence SUV Measurements
What SUV Number Indicates Malignancy?
What Percent Change in SUV on a Follow Up Exam is Significant?
How to Compare Exams With Very Different Background Metabolic Activities?

Chapter 3: The Standardized Uptake Value (SUV)

"The good, the bad & the ugly"

1. What is the SUV & Why Used?

Quantitative vs. Qualitative Assessment
Unitless Measurement
Formula
SUV = ?

2. Variables that Affect SUV

Patient Preparation
Time Between FDG Injection & Scan
Partial Volume Effects
Extravasation
Patient Weight
Size & Position of ROI
Attenuation Correction Artifacts

3. Types of SUV Calculations

Consensus?
Body Weight
Lean Body Mass
Ideal Body Weight
Body Surface Area
Maximum vs. Mean
Average SUV’s by Organ

4. Interpreting the SUV: Threshold Values, “Oncologic Plausibility” & Relative Uptake

Precise Threshold Values?
“Oncologic Plausibility”
Relative Uptake
Assessing Nodes in Lymphoma Cases
Assessing Nodes in Non-Lymphoma Cases
Potential Lesions in Solid Organs
Pulmonary Nodules

5. What % Change in SUV on a Follow Up Exam is Clinically Significant?

The Problem
Current Recommendations

6. How to Compare Sequential Exams With Very Different Background Activities?

Differing Background Metabolic Activities
When Qualitative Assessment is Required
Reporting Language

7. Should We Just Abandon the SUV?

Pros & Cons
“Qualitative” Definitions
- Mild
- Moderate
- Intense
Final Recommendations

Chapter 4: Our Systematic Approach to Reading a PET/CT

"Eat your vegetables"

1. Reading Station & Reading Software

Reading Station
Monitor Set-Up
PET/CT Reading Software
Hanging Protocol

2. General Reading Caveats

Reading in Context (“Oncologic Plausibility”)
Measure Size on CT, Not on PET Images
Abnormality Seen Only on First PET Image
Assess the Patient’s Main Pathology Last
Beware the Ureter

3. Excellent Views: The MIP, Coronal & Sagittal Images

3-D Rotating MIP & Coronal “Quick MIP”
Coronal PET
Sagittal PET

4. Written Annotations While Reading

Numbers, Numbers & More Numbers
Size & SUV Annotation System
Sample Annotation Sheet

5. The Language of Reporting

Goals of Reporting
Lawyers, Lawyers & Lawyers
Sample PET/CT Report
- Negative Exam
- Positive Exam
Patient Questionnaire
Technologist’s Data Sheet

6. The Read

Huge Exam: Requires Systematic Approach
Our “12-Step Reading System”
“The Read” in Action: Sample Case (Video)
Annotations for Sample Case
Final Report for Sample Case

Chapter 5: Normal Physiologic Distribution of FDG

"The essentials"

1. Introduction

To Locate Cancer, First Eliminate:
- Normal FDG-Avid “Structures”
- Benign FDG-Avid “Findings”

2. Head & Neck

3. Chest

4. Abdomen

5. Pelvis

6. Miscellaneous

Images Generated in a PET/CT Exam

Like most things in life, there is both good news and bad news regarding PET/CT scans.

The Good News: It’s a large exam. With only one exam, a patient’s entire body can be reliably evaluated for cancer.

The Bad News: It’s a large exam. There are many thousands of images generated, any one of which might contain the patient’s solitary focus of cancer.

CT Images:

CT images are obtained in the axial plane, with coronal and sagittal reconstructions. A typical study consists of anywhere from 750 axial images for a “skull base to mid-thigh” exam to 1500 images for a “whole body” study.

Non-Attenuation Corrected (NAC) Images:

These images are of limited diagnostic value. They are characterized by increased peripheral uptake along the skin of the patient, increased lung activity and relative decreased radiotracer uptake more centrally in the body.

Attenuation Correction (AC) Images:

In modern scanners, the CT images generated not only serve as the anatomic portion of the exam, but are also utilized for “attenuation correction” of the PET images, generating the much more useful AC PET images used for interpretation.

Maximum Intensity Projection (MIP Image):

Whole body MIP images can be viewed in rotation or static mode and provide an excellent overall assessment of disease (few radiologists are willing to confess the fact that more than 95% of their reported findings can be made from just the coronal MIP image!).

Fused CT & PET Images:

The CT images are fused with the AC PET images in the axial, coronal and sagittal planes – and evaluated using soft tissue, bone and lung window settings.

Final Images To Routinely Interpret:

CT Images, soft tissue windows (3 planes) = 3 series
CT Images, bone windows (3 planes) = 3 series
CT Images, lung windows (axial plane) = 1 series

Fused CT (soft tissue windows) & AC PET Images (3 planes) = 3 series
Fused CT (bone windows) & AC PET Images (3 planes) = 3 series
Fused CT (lung windows) & AC PET Images (axial plane) = 1 series

AC PET Images, axial brain windows = 1 series
NAC PET images (axial plane is usually sufficient) = 1 series
MIP’s (static & rotating)

Therefore, a routine PET/CT exam results in 15 complete sets of images (most of which may be from the top of the head to the bottom of the feet) — clearly an extremely large exam consisting of many thousands of images.

Reading and interpreting a PET/CT exam, therefore, requires time, patience and an extremely organized reading scheme.

Figure 1 (Image 1)