Octreotide Scintigraphy Technique

Updated: Jun 09, 2016
  • Author: Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP; Chief Editor: Gowthaman Gunabushanam, MD, FRCR  more...
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Technique

Octreotide Scintigraphy

The recommended administered activity of 111In pentetreotide is 5 MBq/kg (0.14 mCi/kg) in children and 222 MBq (6 mCi) in adults. The amount of pentetreotide injected is 10-20 mg (this dose is not expected to have a clinically significant pharmacologic effect). 111In pentetreotide is cleared rapidly from the blood (one third of the injected dose remains in the blood pool at 10 minutes and 1% at 20 hours postinjection). [8] It is eliminated principally by the kidneys (half of the injected dose appears in the urine by 6 hours, 85% within one day) and a small amount by the liver (2%). It is unclear whether 111In pentetreotide is removed by hemodialysis. [8, 1]

Images are obtained at 4 hours and 24 hours or 24 hours and 48 hours postinjection. Patients should empty their bladder before imaging. If there is significant bowel activity noted at 24 hours (which may potentially obscure lesions), 48-hour images will be necessary. As tumor-to-background ratio is lower at 4 hours than at 24 hours and 48 hours, some lesions may be missed at 4 hours; nevertheless, the 4-hour images offer information prior to activity in the gut.

Large-field-of-view gamma camera planar images should be obtained.

Planar localized images of the head, chest, abdomen, pelvis, and, if needed, the extremities can be acquired for 10-15 minutes per image, using a 512 x 512 word or 256 x 256 word matrix.

Metastases in the cervical lymph nodes may not be visible on whole-body images. Additional planar localized images of the head and neck (including lateral views) should be obtained.

Using a multidetector gamma camera, SPECT imaging of the appropriate regions based on the clinical history should be performed. Early and delayed SPECT may differentiate bowel activity from pathological lesions. If multiple SPECT images are not possible, a single image acquisition at 24 hours is preferred because of higher target-to-background ratio. [8, 1]

Raw SPECT data should be filtered by applying a low-pass filter, per software manufacturer recommendations. Data reconstruction should be performed by using a ramp filter and attenuation correction. Newer models may allow iterative reconstruction algorithms.

Images should be fused or evaluated with relevant anatomical images (CT or MRI).

The optimal time interval to localize lesions is at 24 hours postinjection or later. Images obtained at 4 hours with high background activity may be important to compare and evaluate abdominal activity at 24 hours. Activity is normally noted in the pituitary, thyroid, liver, spleen, kidneys, bladder, and occasionally the gallbladder. Intestinal activity is normally absent at 4 hours, but images at 24 hours normally show the activity; however, images at 48 hours may be needed to clarify abdominal activity. [8]

Recommendations of the Society of Nuclear Medicine Guideline on General Imaging should be followed in preparation of the report. Additionally, the report should also highlight the relevant history, laboratory evaluation, medications (eg, octreotide, chemotherapy), description, and limitations of the procedure, including false-positive results. [8]

Abnormal octreotide scan. 111In-pentetreotide scin Abnormal octreotide scan. 111In-pentetreotide scintigraphy of a 41-year-old man with ectopic Cushing's syndrome caused by a neuroendocrine carcinoma of the mesentery. Radiotracer accumulation in the left thyroid in 10/2003 (arrow). The mesenterial neuroendocrine tumor became clearly visible in 4/2005 (arrow). Image from Ectopic Cushing' syndrome caused by a neuroendocrine carcinoma of the mesentery, Fasshauer M et al, BMC Cancer 2006, 6:108; available at: http://www.biomedcentral.com/1471-2407/6/108.
Normal octreotide scan. Normal octreotide scan.