Diagnostic Imaging Techniques for Neuroendocrine Tumours

Understanding the role of imaging in NETs

Neuroendocrine tumours (NETs) are a diverse group of malignancies that develop from neuroendocrine cells, which have both hormone-producing and nerve cell functions. Precise diagnostic tools are essential for accurate staging, monitoring, and treatment, mainly due to the complex nature of the condition. 

Diagnostic imaging plays a crucial role in managing NETs, offering vital insights into tumour location, size, spread, and response to treatment. Choosing the appropriate imaging modality is key to achieving the best outcomes for patients.

Neuroendocrine Cancer Australia (NECA), is dedicated to supporting individuals diagnosed with NETs, and their families. NECA offers a wealth of resources, educational programs, and advocacy efforts aimed at deepening the understanding of NETs, improving patient care, and encouraging research advancements. Patients diagnosed with NETs, can engage with NECA’s comprehensive support and information by calling the NET nurse line.

Importance of accurate diagnosis and staging

Accurate diagnosis is fundamental in the management of NETs. The diagnostic process helps:

• Determine the extent of the disease
• Identify metastatic sites
• Assess the involvement of surrounding tissues and organs 
• Guide treatment decisions

Staging classifies the tumour based on its size, location, and whether it has spread to lymph nodes or distant organs. Care teams will use this information to select the appropriate therapeutic approach, whether it be surgery, targeted therapy, or a combination of treatments.

For patients undergoing therapies like somatostatin analogues (SSAs) or peptide receptor radionuclide therapy (PRRT), imaging provides the best possible insights, improving the effectiveness of interventions and enabling timely adjustments to improve outcomes.

Commonly used imaging techniques

Beyond initial diagnosis, imaging is essential for monitoring disease progression and evaluating treatment response in NET patients. Regular imaging allows clinicians to track changes in tumour size, detect new metastases, and adjust treatment plans as necessary. 

There are a range of imaging techniques available to patients and healthcare teams, each of which possesses advantages and disadvantages. Let’s take a look at some of those, and how they form part of a holistic diagnostic practice for managing NETs.

Computed Tomography (CT)

Computed Tomography (CT) is widely used for diagnosing and managing NETs, offering detailed cross-sectional images of the body. It’s particularly effective in detecting primary NETs and liver metastases.

CT constitutes the basic radiological modality for the diagnosis, staging, restaging and surveillance due to its wide availability and detailed contrast-enhanced imaging characteristics of NEN lesions.

• Visualises tumours, and metastatic lesions.
• Effective for detecting NETs in the pancreas, gastrointestinal tract, lungs, and liver metastases.

Advantages:

• Widely available and accessible in most healthcare settings.
• Rapid imaging, allowing for quick assessment.
• Capable of assessing multiple body areas in one session.

Limitations:

• Less effective for detecting small or low-grade NETs that may blend with surrounding tissues.
• Use of contrast agents can pose risks for patients with kidney issues or allergies.

Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI) is highly effective for visualising soft tissues, making it valuable for detecting NETs in organs like the liver, pancreas, and brain.

• Uses strong magnetic fields and radio waves, with no ionising radiation, safer for repeated use.
• Preferred for liver metastases and useful for assessing bone marrow and brain metastases.

Advantages:

• Superior contrast resolution, particularly useful for liver and pancreatic NETs.
• No ionising radiation, making it safer for repeated imaging.
• Highly effective in assessing bone and brain metastases.

Limitations:

• Generally more expensive and less widely available than CT.
• Longer imaging times, which can be uncomfortable for some patients.
• Some metal implants are not compatible with MRI scanners

Positron Emission Tomography (PET)

Positron Emission Tomography (PET) combined with CT, and 68Ga-DOTATATE, is highly sensitive for detecting NETs by targeting somatostatin receptors.

Advantages:

• 68Ga-DOTATATE PET/CT provides precise imaging of small and hard-to-detect NETs.
• PET/CT with 18F-FDG is particularly useful for aggressive, high-grade NETs and NECs.
• Offers a comprehensive tumour assessment by highlighting active tumour sites.

Limitations:

• High cost and limited availability, especially for advanced PET/CT imaging.
• Involves radiation exposure, although it is generally low.

Ultrasound

Ultrasound is a non-invasive technique that uses high-frequency sound waves to create images of internal organs, particularly useful for detecting liver metastases and some primary NETs.

Diagnostic ultrasound (US) as well as contrast-enhanced ultrasound (CE-US) can play a role in work-up of liver metastases in rare cases when CT and MRI findings are equivocal or not feasible.

Targeted endoscopic ultrasound (EUS) is frequently used for detection, further work-up and to guide tissue

sampling of small primary lesion

Advantages:

• Non-invasive, with no radiation exposure.
• Real-time imaging, useful for guiding procedures like biopsies.
• Accessible and cost-effective, often used as a first-line imaging modality.

Limitations:

• Less effective in visualising deep-seated tumours or those in challenging locations.
• Operator-dependent, meaning the quality of the images can vary.
• Limited in its ability to provide detailed images compared to CT or MRI.

Imaging for monitoring treatment response

Imaging doesn’t end at diagnosis. It’s also very effective for monitoring how treatment of NETs is progressing, while offering insights as to how treatment could be improved.

Tracking tumour shrinkage and metastasis

Monitoring treatment response in NET patients is a critical aspect of ongoing care. Imaging techniques like CT, MRI, and PET/CT are used to track tumour shrinkage, assess the stability or progression of metastatic lesions, and detect new areas of disease. 

Accurate imaging can help healthcare teams improve the effectiveness of treatments such as SSAs, chemotherapy, or PRRT. It’s a great opportunity for everyone involved to make informed decisions about adjusting or changing treatment regimens.

Assessing overall effectiveness of treatments

Imaging also plays a key role in evaluating the effectiveness of various treatments for NETs. Here are some examples:

• After PRRT, 68Ga-DOTATATE PET scans are often used to assess the reduction in tumour activity
• CT or MRI can provide information on changes in tumour size 

This information is crucial for determining whether a treatment is working, needs to be continued, or if alternative therapies should be considered.

Challenges and considerations of imaging for NETs

As with all types of diagnostic tools for assessing all types of cancer, the methods used to identify NETs come with a raft of challenges and considerations. Patients, their families, and care teams should understand these before proceeding down an avenue of treatment.

Balancing sensitivity and specificity

One of the challenges in imaging NETs is balancing sensitivity (the ability to detect all true positives) with specificity (the ability to exclude false positives). 

Radiation exposure 

Cumulative radiation exposure associated with repeated imaging, is a concern, particularly in patients undergoing long-term monitoring. While techniques like MRI and ultrasound do not involve radiation, CT and PET scans do. 

Healthcare teams must balance the need for accurate and frequent imaging with the potential risks of radiation exposure, especially in younger patients or those requiring lifelong surveillance.

Access, affordability, and availability

Access to advanced imaging techniques, such as PET/CT with 68Ga-DOTATATE, can vary based on geographic location and healthcare resources. 

In some areas, these advanced imaging options may be limited or unavailable, making it challenging for patients to receive the most accurate diagnosis and monitoring. 

Additionally, the cost of advanced imaging can be a barrier for some patients, highlighting the need for equitable access to these essential diagnostic tools.

Impact on patient care

To give patients the best chance at effective treatment, it’s important to understand how imaging impacts on long term patient care.

High-quality imaging is critical for improving diagnostic accuracy in NET patients. By providing detailed and accurate information about tumour characteristics and spread, imaging helps personalise treatment plans, giving patients the most appropriate and effective therapies. 

Advanced imaging techniques can also help reduce unnecessary interventions by providing clear and accurate information about the extent of the disease. For example, detecting small, slow-growing NETs that do not require immediate treatment can prevent unnecessary surgeries or therapies..

Early detection of NETs through advanced imaging can significantly enhance a patient’s quality of life. By identifying tumours at an earlier stage, when they are more treatable, imaging can lead to more effective interventions.

Research and future directions

The field of imaging is continually evolving, with ongoing research focused on improving the sensitivity and specificity of imaging techniques for NETs. Innovations include:

• Development of new radiotracers for PET imaging
• Use of artificial intelligence (AI) to enhance image analysis
• Imaging biomarkers to better understand NET biology 

These advancements have the potential to transform the way NETs are diagnosed and managed, leading to better patient outcomes.

Ongoing clinical trials are investigating these biomarkers’ potential, which could lead to more personalised and targeted therapies for NET patients.

Further information and support for people diagnosed with NETs is available by calling the NECA NET nurse line.