PET-CT combines functional PET imaging with anatomical CT imaging. A PET-CT scan involves fasting for 4-6 hours before injection of 18F-FDG tracer, followed by a whole body scan 40-60 minutes later lasting 13-17 minutes. Standardized uptake values (SUVs) are used to measure tracer uptake in tissues, with values over 2.5 suggesting malignancy. Dual time scanning one hour later can identify if SUV increases by 10% indicating malignancy or remains the same/decreases indicating benignity. Reference tissues like blood pools and livers are used to compare lesion uptake values to determine if they are higher, suggesting malignancy, or equal/lower, suggesting benignity.

1. Technique

2.  PET-CT is the fusion of functional (PET) and
anatomic (CT) information
 The PET-CT scanners are full ring coincidence
detectors, the P.E.T. portion mounted
together with CT system.

3.  Fasting for 4-6 h before injection of 18F- FDG.
 The scan was performed 40-60 min after IV
injection of 18F- FDG
(0.1 millicurie/kilogram (mCi/kg); maximum
dose = 20 mCi/kg).
 The patients in supine position.
 A whole body examination from skull base to
mid thighs.
 The total examination time range between 13
and 17 minutes.

4.  The blue-purple rectangle
represents CT coverage during
the study,
 Each overlapping green
rectangle represents PET
coverage.
 Six to seven bed positions are
required for PET coverage of
the neck, chest, abdomen, and
pelvis

5. Standarized uptake value:-
 It is used for relative tissue uptake of FDG
tracer.
 SUV threshold value used for malignancy is
(> 2.5) .
 Formula:-
SUV= Tumor activity concentration [mCi/ml]
X body weight (g)/injected dose FDG [mCi ].

6.  Many benign infectious/inflammatory
processes (e.g: TB granuloma) will have a high
SUV value…..false positive results.
Dual time scanning :-
Delayed imaging is performed one hour following the
initial scan,
If SUV increased by 10%= malignancy.
If stationary or decreased= benign lesion.
Many slowly growing malignant processes
(e.g: BAC and carcinoid) may have minimal
uptake, and low SUV values….false negative
results.

7. Reference tissue :-
 - A number of tissues have been advocated as
reference tissue including, blood pool, liver,
lung and cerebellum.
 - Scientists found that mediastinal blood pool
showed the least inter-patient coefficient of
variance

8.  If the uptake of the lesion is
higher than the reference
tissue…. It is malignant.
Fig (A)- higher uptake compared
to the liver (RCC).
Fig (B)- higher uptake compared
to the mediastinal blood pool
(bronchogenic ca).

9. If the lesional uptake is
equal or lower to the
reference tissue….it is
benign.
Fig (A) - uptake is equal to that
of liver (Bilateral adrenal
hyperplasia).
Fig (B) - uptake is lesser to that
of liver (renal cyst= photopenic)

10.  If the SUV of the lesion is higher than the
reference tissue…. It is malignant.
Fig (A)- Lesion SUV ~ 18 compared
to the liver (SUV~3.8).
Fig (B)- Lesion SUV~ 20 compared to
the mediastinal blood pool (SUV~3.5).

11. Thank you