A 69-year-old male presented with a large, 5-cm,
fixed left-neck mass. A biopsy identified squamous cell carcinoma and
suspected left laryngeal cancer. There was a question of small lung
nodules on a computed tomography (CT) scan obtained at another hospital.
A positron emission tomography/CT (PET/CT) scan was obtained to
evaluate primary neck nodes and distant metastatic lesions.
PET/CT images were obtained with the following protocol: Approximately
90 to 120 minutes following the IV injection of
16.2 mCi of
F18-fluorodeoxyglucose, 3-dimensional TOF (time of flight)imaging was
obtained from the skull vertex to the lung apices and from the lung
apices to the upper thighs with CT attenuation correction using a
dedicated closed-ring PET system Gemini TF Big Bore. The images revealed
avid uptake in the primary tumor located within the left neck and
adjacent local lymph nodes (Figure 1). In addition, the images revealed
PET-avid nodules within lungs (Figure 2). The presence of these nodules
changed the stage of this tumor.
Metastatic PET-avid nodules within lungs
staging depends on accurate diagnosis, and this can only be done if we
can identify even the smallest foci of primary, recurrent or metastatic
tumors. The importance of providing PET imaging is paramount to patient
care. Neurology, cardiology, and oncology patients all benefit from this
advanced technology. With PET imaging in oncology, we are constantly
looking to improve image quality, reduce dose, and have faster
acquisition times. In the past, PET was not recommended for evaluation
of pulmonary nodules < 8 mm in size.1 In this example, we
have demonstrated pulmonary nodules as small as 3.5 mm (Figure 3). A
lesion this size has < one-tenth the volume of an 8-mm lesion.
PET scanners operating in 2D mode have low energy resolution and limit
scattered events, thus limiting the system sensitivity by as much as
80%. Astonish TF allows us to fully operate in 3D mode, allowing higher
sensitivity, therefore the ability to obtain adequate image quality with
low dose.2 The Astonish TF enhances the combination of multiple reconstruction algorithms.
TOF technology allowed us to characterize small lesions that may not
have been large enough to characterize on older imaging systems. The
small metastatic lesions to the lung may have been dismissed as benign,
and the patient may not have been treated appropriately.