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ECR 2019 / C-2625
Hybrid imaging in neuroendocrinal tumours, an overview
Congress: ECR 2019
Poster No.: C-2625
Type: Educational Exhibit
Keywords: Cancer, Diagnostic procedure, PET-CT, Molecular imaging
Authors: M. M. A. Rezk; Cairo/EG
DOI:10.26044/ecr2019/C-2625

Findings and procedure details

I.             

Conventional:Computed tomography CT

CT scans are usually the initial imaging study.

 

 

PROS:

Would be anatomical useful modality for disease staging and surgical planning. Primary NETs and their metastases are generally hyper-enhancing, best seen in the arterial phase of a triple phase CT scan

Useful for operative planning, disease staging

 

CONS:

Not a functional study; weak in detection of the primary in 95% of cases

High radiation exposure

 

Optimal imaging of NETs requires IV contrast

 

 

Magnetic resonance imaging

PROS:

 

MRI is the best to detail hepatic metastases in NETs

Would be useful good for the primary pancreatic NETs.

Good pancreatic resolution

No radiation exposure

Gadolinium contrast is safer if renal dysfunction

 

CONS:

 

not useful in the detection of primary small bowel lesions or their associated lymphadenopathy.

Poor assessment of GI tract, mesenteric lesions

Cannot image patients with metal implants

Not a functional study

 

18FDG positron emission scanning

PROS :

 

Good for high grade NETs

Good anatomic resolution

 

 

CONS:

Unfortunately, Most NETs tend to be metabolically inactive and fail to take up the tracer 

 

Somatostatin receptor-based imaging techniques

 

 

  • Somatostatin is secreted by neuroendocrine cells, activated immune cells and inflammatory cells.
  • It affects its antiproliferative and antisecretory functions by binding to one of five types of somatostatin receptors (SSTRs) being highly expressed on well-differentiated NETs, and their ubiquity on NET cell surfaces makes them ideal targets for treatment and imaging. 

Octreotide analog studies

  • 111In-DTPA-D-Phe-1-octreotide is the ligand used by the modern OctreoScan. This tracer was easier to prepare, cleared primarily by the kidneys ; solving the problem of accumulation within the GI tract of the old one 123I tracer, and had a much longer half-life (optimal image acquisition occurs at 24 h post-injection of the radiotracer).

    Due to OctreoScan being a functional (i.e., SSTR-specific) full body scan, it can often identify lesions that were missed by CT or MRI.

    The OctreoScan is a useful, especially when fused with SPECT and CT. 

 

PROS:

 

  • Functional study
  • Level of uptake can be graded
  • Provides whole body image (on one shot single study)
  • Predicts response to therapy

 

 CONS:

 

  • High background in Gl tract, which may obscure midgut NETs
  • Patient must be scanned twice in 24 h
  • Low anatomic detail
  • Need to hold Octreotide prior to scan

DOTA-PET

The newest advance in somatostatin receptor-based imaging is the introduction of 68Ga-labeled radioligands, whose uptake is measured by PET scan.

 

68Ga-DOTATOC -PET VS OctreoScan

·        easier and cheaper to synthesize than standard octreotide-analog based ligands,

·         scanning 1 h postinjection vs OctreoScan, (which requires patients to be scanned at 4 and 24 h postinjection),

·         and allow for quantifying the uptake of the ligand within the lesions.

·         superior in spatial resolution

·         68Ga-PET studies are fused with CT to improve anatomic localization.

·         universally demonstrated the superiority of 68Ga-PET in detection of NET primary tumors and metastases.

·         68Ga-DOTA PET imaging can be used to determine which patients might benefit from Octreotide and PRRT.

 

 

PROS

·         Functional study

·         Uptake can be quantified

·         Good anatomic resolution

·         Provides whole body image

·         Image acquired over 2 h

·         Predicts response to therapy

CONS

·         Physiologic uptake in uncinate process, pituitary, spleen and kidneys may be confused for tumor uptake

 

·         Available at a limited number of centers 

 

 

Radioiodinated (123I) metaiodobenzylguanidine (MIBG):

 

  • used to image catecholamine-secreting NETs such as pheochromocytomas & paragangliomas used to confirm their diagnoses and define the extent of metastatic disease

PROS

  • Functional study
  • High specificity for pheochromocytoma, paraganglioma, and glomus tumors
  • Provides whole body image
  • Predicts response to therapy

CONS:

 

  • High background
  • Low anatomic detail
  • Many medications can interfere with the scan and must therefore be held
  • Thyroid must be blocked prior to scan
  • Patient scanned 24 h after contrast administration

 

 

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