Diagnostic Imaging techniques

Lecture Overview

  • Title: Diagnostic Imaging: Techniques and Applications in Theranostics

  • Course: BSc ATT Y2, Pharmacology and Theranostics module

  • Date: November 11th, 2025

  • Lecturer: Dr. Ingmar Schoen

  • Email: ingmarschoen@rcsi.ie

Learning Outcomes

  • At the end of this lecture, you will be able to:

    • Discuss the routine usage of medical imaging techniques for diagnostic purposes.

    • Briefly describe the basic working principles of various imaging techniques:

    • Ultrasound

    • X-ray

    • CT scan

    • Digital mammography

    • MRI

    • Nuclear imaging (PET and SPECT)

    • Compare and contrast different approaches to incorporate medical imaging into therapies.

    • Define ‘theranostic radiopharmaceuticals’ and provide examples.

    • Distinguish the working principles of therapeutic low level ultrasound versus high-intensity focused ultrasound.

    • Discuss the emerging role of nanoparticles in creating new application opportunities of medical imaging techniques for therapeutic purposes.

Outline

  • Traditional scope of diagnostic imaging

  • Medical imaging techniques

  • Old, new and emerging applications of medical imaging in theranostics

Traditional Scope of Diagnostic Imaging

  • Example: Cancer treatment lifecycle

    • Asymptomatic stage

    • Diagnostic workup

    • Post-treatment screening

    • Uses of medical imaging for:

    • Early detection

    • Initial diagnosis

    • Confirmation of diagnosis

    • Staging

    • Follow-up evaluation of treatment success

Medical Imaging Techniques

Ultrasound

  • Definition and Principles:

    • Ultrasound consists of longitudinal pressure waves with frequencies above the human threshold of hearing.

    • Utilizes piezoelectric elements that convert alternating voltages into vibrations, sending out ultrasound.

    • Waves at media interfaces may be transmitted, absorbed, or reflected based on the media's acoustic impedances.

    • Reflected pulses are received and converted into voltage signals by piezoelectric elements.

  • Imaging Mechanism:

    • Follows the principle of sonar; delayed echo indicates greater distances to reflecting boundaries.

    • A transducer array scans wave direction along a line, with line x depth scans producing a 2D image known as a ‘B-scan’.

    • Other modalities include motion detection (‘M-scan’, e.g., heart valve) and velocity measurement (‘Doppler scan’, e.g., blood flow).

    • Diagnostic ultrasound operates at a frequency range of 3-10 MHz.

  • Applications:

    • Diagnostic ultrasound uses pulse intensities around 0.01extWcm−20.01 ext{ W cm}^{-2}; no harmful effects reported.

    • It is favored for being fast, inexpensive, and non-invasive.

X-ray

  • Definition and Mechanism:

    • X-rays are high-energy electromagnetic radiation (photons) with energies between 10−100extkeV10-100 ext{ keV}.

    • Produced by bombarding material with electrons, generating a broad spectrum termed ‘Bremsstrahlung’.

  • Interaction with Tissue:

    • X-rays interact with tissue atoms, creating tissue contrast and artifacts based on their energy levels:

    • Transmitted (no interaction)

    • Absorbed/attenuated (photoelectric effect)

    • Scattered (Compton scattering)

    • Detectable contractions and artifacts depend on the imaging setup and energies used.

  • Image Quality:

    • Better tissue contrast achieved at lower X-ray energies due to reduced scattering.

    • Higher energies penetrate deeper tissues.

Computed Tomography (CT)

  • Definition:

    • Advances X-ray by computing attenuation in each voxel, allowing for 3D imaging rather than single 2D projections.

  • Data Collection:

    • Requires gathering a large dataset of signals from multiple angles using digital detectors.

Digital Mammography

  • Purpose:

    • Utilizes X-rays to spot small calcifications and aberrant breast tissue structures associated with cancer.

  • Methodology:

    • Uses low-energy X-rays for optimal soft tissue contrast; digital or analog films capture images.

  • Latest Technology:

    • Digital breast tomosynthesis (DBT) allows for detailed outline delineation of masses.

Magnetic Resonance Imaging (MRI)

  • Principle of Operation:

    • Employs strong magnetic fields (1-5 T) to align nuclear magnetic moments (specifically proton spins).

    • Short radiofrequency pulses disrupt this alignment, and relaxation to equilibrium provides image contrast.

  • Tissue Contrast:

    • Contrast is based on different relaxation times (T1 and T2) between tissues:

    • T1 and T2 relaxation times vary, impacting imaging quality and clarity.

  • Comparison to CT:

    • MRI offers superior soft tissue contrast compared to CT, making it invaluable for specific diagnostic purposes.

Nuclear Imaging: PET and SPECT

  • PET (Positron Emission Tomography):

    • Involves using radiotracers, radiopharmaceuticals that bind to specific cells labeled with radionuclides.

    • Commonly used radiotracer: 18FDG (fluorodeoxyglucose), known for its uptake by metabolically active cancer cells.

  • Mechanism:

    • Upon radioactive decay, a positron emitted by 18F annihilates with an electron, leading to the emission of two gamma ray photons.

    • The detection process reconstructs 3D images based on the location where the photons were emitted.

  • SPECT (Single Photon Emission Computed Tomography):

    • Utilizes radiotracers that emit single gamma photons (e.g., 99mextTc^{99m} ext{Tc}, 123extI^{123} ext{I}, 131extI^{131} ext{I}) detected via a gamma camera.

    • SPECT is less sensitive than PET but more cost-efficient.

Application in Theranostics

  • Definition:

    • Theranostics refers to a field that combines diagnostic imaging with therapeutic intervention, primarily applied in cancer treatment.

  • Applications:

    • Imaging to inform treatment modalities and adjustments for patient-specific therapeutic strategies.

    • Use of imaging to target previously undetected tumors, influencing surgical decisions.

Further Focus on Imaging Techniques

Image-Guided Surgery

  • CT or MRI Navigation:

    • Utilizes scans registered to anatomical reference points tracked by cameras during surgery.

    • Allows for precise navigation through anatomical structures, essential in complex surgeries like brain or spine procedures.

Near Infrared (NIR) Fluorescence

  • Real-Time Feedback:

    • Uses NIR fluorescent contrast agents to provide live updates during surgery through the emission of light detected by cameras.

Sentinel Node Mapping

  • Breast Cancer Example:

    • Involves injecting non-targeted tracers into a tumor to track lymphatic spread, enhancing the ability to identify and manage metastasis.

Conclusion and Learning Summary

  • Reiterate main learning outcomes and emphasize the significance of medical imaging in both diagnosis and therapeutic strategies, particularly in innovative contexts like nanotechnology in imaging.

Further Reading and Resources

  • Beyer et al. 2020, Cancer Imaging trends

  • K. Wang et al. 2023, Fluorescence imaging in surgery

  • C. Barca et al. 2022, Theranostic advancements

  • K. Entzian and A. Aigner. 2021, Ultrasound and drug delivery studies

  • Online resources and medical articles for additional insight into theranostics and imaging methodologies.