New Concepts in Molecular Imaging

New Concepts in Molecular Imaging

Advanced imaging and hybrid modalities are evolving to aid and personalize future patient population care.

Advanced imaging and hybrid modalities, such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET)/CT, and single-photon emission computed tomography (SPECT)/CT are showing significant growth and will continue to do so. There are ongoing studies and data that demonstrate the value of molecular imaging and nuclear medicine solutions in both traditional and new use cases. Today, the value in these innovations and the added confidence they provide in informing better patient care is more widely recognized. As a result, PET/CT volume in particular is expected to rise steadily over the next 10 years, driven by new indications, novel tracers obtaining regulatory approval, and expanded insurance coverage.

It is valuable citing excerpts from an article, Translational Molecular Imaging Computing: Advances in Theories and Applications, authored by Jinchao Feng, Wenxiang Cong, Kuangyu Shi, Shouping Zhu, and Jun Zhang, research experts in the field.

Molecular imaging is capable of revealing cellular and molecular features of organism and disease in vivo, meeting the increasing demands in the noninvasive understanding of biological processes. Computational technologies are essential for the development of cutting-edge molecular imaging. In the past, the advancement of molecular imaging computing has been well recognized and continuously extends the application potential of molecular imaging.

Major progress has been made in molecular imaging computing, including applications, high-performance computing technologies, method, and algorithm improvement.

Computed tomography (CT) is one of the commonly used imaging techniques. Now, the use of CT has increased rapidly. However, it involves radiation doses during a CT exam, which are harmful to the patient. When radiation dose decreases, the relative noise in CT images will increase, which deteriorate the image quality. Therefore, how to reduce CT scanning dose of patients while maintaining the same image quality is a challenging problem. A total variation minimization method was applied, which improved the image quality of CT by incorporating prior images. And an improved smoothed-norm regularization method suppressed artifacts and obtained better edge preservation in reconstructed images.

Optical tomography (OT) is one of the most sensitive molecular imaging techniques and is especially suited for preclinical studies. Systematic reviews of OT will improve researchers’ understanding and skills in utilizing the technique. Banghe Zhu and Anuradhu Godavarty from The University of Texas Health Science Centre and from Florida International University respectively, reviewed technical aspects of fluorescence-enhanced optical tomography (also called fluorescence molecular tomography, FMT) including the principal, measurement approaches, forward model, and inverse problem. They mentioned that the inverse problem of FMT is severally ill-posed and underdetermined due to nonuniqueness and a limited number of measurements. To alleviate the ill-posedness of FMT, H. Yi et al. presented a feasible region extraction strategy based on a double mesh. To increase computational efficiency, D. Chen et al. developed a sparsity-constrained preconditioned Kaczmarz reconstruction method.

Cherenkov luminescence imaging (CLI) is an emerging imaging modality, which captures visible photons emitted by Cherenkov radiation labeled with -emitting radionuclides, using widely available in vivo optical imaging systems. In other words, CLI uses optical means to provide information of medical radionuclides used in nuclear imaging based on Cerenkov radiation. However, the exceptionally weak Cerenkov luminescence from Cerenkov radiation is susceptible to lots of impulse noises. In the paper contributed by X. Cao et al., a temporal median filter is proposed to remove this kind of impulse noises. Results of in vivo experiments demonstrated that the temporal median method can effectively remove random pulse noises induced by gamma radiation and achieve a robust CLI image.

The image resolution of pure OT or CLT is relatively low because of the high diffusion of photons in biological tissues. To improve image resolution, a new hybrid imaging modality, X-ray luminescence computed tomography (XLCT), has been developed. XLCT utilizes X-ray luminescent nanophosphors (NPs) as imaging probes. NPs can be excited with a pencil, fan, or cone beam of X-rays. Cone beam XLCT can realize fast XLCT with relatively low scanning time compared with pencil beam XLCT. However, the reconstruction of cone beam XLCT is also an ill-posed problem. To alleviate the ill-posedness of XLCT, D. Chen et al. developed a hybrid reconstruction algorithm with KA-FEM method. In vivo mouse experiment was used to evaluate the feasibility of the method.

Multimodality molecular imaging is now playing an important role in preclinical and clinical research, which utilizes the strengths of different modalities and yields a hybrid imaging platform with benefits superior to those of any of its individual components, considered alone. In the paper contributed by Y. Liu et al., a dual-modality imaging system which combines multispectral photoacoustic computed tomography and ultrasound computed tomography was developed to reconstruct functional and structural information of human finger joint systems. Phantom and in vivo results illustrated that the bones, the blood vessels, and the subcutaneous tissues could be reconstructed using the dual-modality system.

Second Opinion
Futuristic CT Scan – Dual layer Detector CT – True Spectral CT

In clinical practice, CT has become an essential tool with many applications in diagnosis and disease follow-up, and the assessment of response to therapy. Until now, CT with its conventional poly energetic grayscale images based upon Hounsfield units has been limited by its inability to quantify contrast agents and to discriminate between various body materials.

New spectral CT is the first and the only dual-layer detector CT built from the ground up for spectral imaging so no upfront decision-making is necessary to obtain spectral information. Because use of dual-layer detector spectral CT requires no pre-scan determination, if incidental abnormalities are encountered there is no need to call the patient back for additional imaging. On-demand spectral analysis of a region of interest allows the physician to further interrogate incidental findings.

Spectral detector has the ability to simultaneously distinguish between X-ray photons of high and low energies. This spectral analysis allows the discrimination of materials consisting of specific atomic numbers, such as iodine or calcium. Various elements are assigned individual colors, allowing them to be visually distinguished on CT scans. Because the acquisition of spectral data is dependent on the detector rather than the X-ray tube, there is no need to decide to use a spectral protocol in advance of performing a scan. The patient is scanned using established workflows, and a conventional anatomical image can be generated and interpreted. Data generated during scanning with spectral CT are fully DICOM 3.0-compliant, and images can be sent to the PACS where they can be archived for retrospective spectral reconstruction and evaluation. Spectral image reconstruction can include image types such as mono energetic (MonoE), iodine quantification, and images that map the effective atomic number of the tissues in question.

Using traditional CT, a patient first undergoes a non-contrast scan and is then scanned after injection of contrast agent to acquire contrast-enhanced data for diagnostic purposes. A scanner like Philips IQon spectral CT requires only a single contrast scan. Because spectral CT can, for example, identify iodinated contrast agent, during image reconstruction iodine can be virtually removed from the image.

In conventional CT imaging, the polychromatic beam is a source of beam-hardening artifacts. By using the simultaneous detection of low- and high-energy signals, it is possible to suppress beam-hardening artifacts.

Most important is therapy response in oncology. You want to know if a tumor is responding in the correct way. Is the patient getting an advantage from treatment? Perhaps one of the areas where the application of spectral CT may have a major clinical impact is in the evaluation of tumor response to therapy.

Dr SS Doda,
Hony Radiologist to the President of India,
Sr. Consultant and Director,
Dr Doda’s Diagnostics & Healthcare, New Delhi

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