Imaging Instrumentation Trends In Clinical Oncology

The second leading cause of death worldwide is attributable to cancer, with 17 million new cases per year. One in three people gets impacted by cancer and just under 10 million succumb to cancer every year.  The increasing trend of cancer is causing a significant burden on healthcare as the cost is driven by complex and long-lasting therapies. Diagnosis, treatment, patient workup, and care in addition to the loss of workforce are constantly rising and account for 10% or more of gross GDP with variations across countries. Hence the focus on early and accurate diagnosis in clinical oncology. Non-invasive detection of cancerous tissue through patient-specific morphology and functional molecular pathways has become the mainstay for referring oncologists to support therapy management decisions. Stand-alone anatomical and functional oncology imaging has moved towards integrating molecular image information through various methods, including anatometabolic imaging (PET/CT), advanced MRI, and optical or ultrasound imaging.  There has been a steep increase in imaging compared to other physician-provided services.

Hybrid imaging methods

Non-invasive imaging yields anatomical information that enables the detection of cancerous tissue in vivo. If there is no morphological alteration, it is difficult to detect oncological diseases from plain anatomical images and can be identified by virtue of molecular and metabolic perturbations. 

Nuclear medicine techniques, that rely on the tracer principle such as Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) have taken center stage in the diagnostic management of cancer. Labelling minute amounts of a biomolecule of choice such as glucose with a radioactive isotope enable labelled biomolecules to be traced by means of emitted radiation without disturbing normal tissue function. Optical imaging makes use of fluorescent molecular probes and ultrasound of targeted microbubbles to highlight signaling pathways and differential anatomies respectively. Even though nuclear medicine imaging is highly sensitive and specific they yield images of tracer distribution that are of lower spatial resolution than CT or MRI owing to fundamental differences in detection principles of molecular and anatomical imaging. This has led to the emergence of hybrid imaging methods, that include the physical combination of PET and CT (PET/CT), SPECT and CT(SPECT/CT), or PET and MRI (PET/MRI). General practice is to support imaging with bioptic sampling to confirm the diagnosis. Time and accuracy of diagnosis and full understanding of cancer phenotype with a minimally invasive procedure is ideal and desired for precision medicine that enables the choice of appropriate therapy depending on the stage and biological features of the disease.

PET imaging and instrumentation trends

Noninvasive imaging technique such as PET provides visual and quantitative information on molecular pathways. Imaging is done following the injection of a radiotracer (biomolecule labelled with a neutron-deficient radioisotope). The positron travels a short distance before it annihilates termed the positron range. The spatiotemporal distribution and absolute concentration of the tracer are determined through the detection and reconstruction of annihilation events. PET detectors can now be manufactured with very fast scintillation materials and produced in modules for use in PET/CT and PET/MRI combinations. When designed with SiPM, it can improve spatial resolution and partial volume effects. TOF and advanced image reconstruction algorithms create flexibility in image protocol designs and help push the image quality even in low count situations which help in signifying even early time point measurements shortly after tracer injection and with parametric imaging.  PET imaging in combination with CT and MRI, PET/CT, and PET/MRI provides suitable information augmenting clinical practice. The latest PET/CT permit shorter acquisition times, lower administered radiotracer amount, and easily repeated imaging of any region of the body. Therefore, transform PET imaging from a diagnostic tool to a screening tool. PET/MRI comparatively is evolving slowly.

SPECT imaging and instrumentation trends

Tomographic images of functional and metabolic pathways in the body can be generated using non-invasive molecular imaging SPECT. SPECT relies on physical collimators to generate projection data for the localisation of the SPECT tracer. Correction and image reconstruction approaches have made SPECT quantitative recently. SPECT/CT enables the advantage of localisation and other complementary CT information superimposed with SPECT in addition to attenuation correction. Bone SPECT and mIBG SPECT can aid staging and disease progression. Large volume SPECT cab benefit from dosimetry application to ensure dosimetry of tumors and organs at risk in a timely manner. SPECT/MRI has the potential to manage patient motion and improve image reconstruction and delineate areas of interest that can be useful for performing partial volume correction of the emission data. SPECT hardware design is set to evolve rapidly, together with development with collimation and image reconstruction is set to improve the specificity and reduce examination time. There is potential for greater demand in SPECT for both radiation dose assessment and the ability to monitor treatment response. Quantitative SUV SPECT will enable more precise diagnosis.

CT imaging and instrumentation trends

CT generates 3-D, high-resolution images that enable the depiction of alteration of standard anatomy or alterations of dynamic processes such as restricted intravenous contrast enhancement. Important hemodynamic parameters such as blood flow, volume, or permeability surface area product can be studied. CT imaging is applicable for diagnosis, staging, restaging, and follow-up. Evolution in technology enables images with spectral information at significantly higher spatial resolution and greatly reduced noise. This positively impacts oncology imaging applications such as assessing the thorax, or characterisation of bone metastases. This will also improve characterisation of low-contrast lesions. Dual-energy CT (DECT) enables the detection of tumors, characterisation of lesions, and for surrogates of perfusion measurements. DCET is available in mid-range and premium systems. Technology in CT is moving towards images with spectral information at significantly higher spatial resolution and greatly reduced noise. This will enable assessment of the thorax or characterisation of bone metastases.

MRI instrumentation trends

MRI has the advantage of providing multifaceted and excellent image contrast that works well for soft tissues. It can be done in any orientation without postprocessing image reformatting. Gadolinium-based contrast agents have been the mainstay for oncological investigations such as detection, characterisation, and staging. Moving blood or CSF in MR angiography can detect and depict vascular abnormalities. Time of flight (TOF) MRA doesn’t need contrast agents and relies on inflow enhancement of blood signals and other saturation techniques. MR Elastography can help in staging liver fibrosis and differentiation between benign and malignant tumors. Diffusion-weighted imaging (DWI) measures the anisotropy of the underlying tissues and is helpful for preoperative planning by showing the relationship between brain tumors and adjacent white matter fiber tracks. Chemical exchange saturation transfer (CEST) is sensitive to cancer metabolism and progression that can not only detect, and characterize but also assess treatment response. MRI has become the first choice for the detection, characterisation, and staging of cancers including that of the brain, spine, liver, prostate, rectum, and breast. 

PET/MRI combines high soft tissue contrast of MR with the simultaneous acquisition of PET data that is useful for local staging and treatment assessment of several gynaecological and prostate tumors.

US imaging and instrumentation trends

US imaging is usually the first diagnostic modality for patient work-up due to ease of use, widespread availability, lack of radiation, real-time imaging, low cost, and high mobility of the devices for oncology radiologists. US elastography (USE) differentiated between benign and malignant lesions of the breast and thyroid. Contrast-enhanced US (ceUS) in clinical practice can help characterize liver lesions. Therapeutic high-intensity focused ultrasound (HIFU) applications have been approved by FDA for 6 indications including uterine fibroids, malignant and benign prostate lesions, and bone metastasis specific to oncology. Motion-model Ultrasound Localization Microscopy (mULM) has been applied to patients with breast cancer to monitor their response to therapy. Molecular ultrasound imaging (MOUS) can detect therapy response even earlier to ceUS during anti-angiogenic therapies. Studies have shown BR55, microbubbles targeting the endothelial biomarker vascular endothelial growth factor receptor 2 (VEGFR2) detection useful in ovarian, breast, and prostate lesions. 

Optical imaging and instrumentation trends

Optical imaging in the invasive intra-surgical application can guide precise tumor excision and help to spare vessels to avoid excessive bleeding. Fluorescence markers enhance image contrast in optical imaging and support tumor detection and image-guided interventions during bioptic sampling and surgical excision. This is critical as inadequate tumor resection is reported in 20-70% of cases in breast cancer surgery or 85% of head and neck surgeries. Optical coherence tomography (OCT) has penetration down to 2 mm and allows one to determine the cancer stage by assessing the actual invasiveness of tumor growth. Fluorescence medical imaging (FMI) is helpful for intra-surgical guidance and has become an important diagnostic tool for brain tumor resection and detection and delineation of bladder cancer.

Conclusion

In the era of personalized medicine, we are dedicated to providing radiology solutions that integrate imaging and non-imaging methods. Imaging modalities are the mainstay to provide information covering anatomical, functional, and molecular data. The introduction of hybrid modalities has become feasible and cost-effective further optimizing management in oncology practice.