Radiology Imaging 2024-2025 Notes

Introduction to Radiology

• Diagnostic Approach Evolution:
  • 1900s: Interrogation, clinical examination, surgery.
  • 2024: Interrogation, clinical examination, biology, medical imaging, surgery (or not).

Medical Imaging

• Definition: Techniques for creating images of the inside of the human body for diagnostic and therapeutic purposes.
• Aspects:
  • Morphology of organs: projection or cross-sectional imaging, volume representation.
  • Functioning of organs: dynamic imaging, functional imaging.
  • Structural components: high-resolution imaging, molecular imaging.

Medical Imaging Specialties

• Radiology
  • Conventional Radiology
  • Echography (Ultrasound)
  • Computed Tomography (CT/TDM)
  • Magnetic Resonance Imaging (MRI)
• Nuclear Medicine
• Radiotherapy
  • Diagnostic and Therapeutic aspects.

Other Imaging Techniques

• Endoscopy (Gastroscope, Duodenoscope, Oesophage, Stomach, Lung)
• Genetics
• Anatomo-Pathology

Radiology Principles

• Relies on different physical principles:
  • X-rays: Conventional radiography, Tomodensitometry (TDM/Scanner).
  • Ultrasound: Echography (US).
  • Magnetic Resonance: MRI.
• Common Principles:
  • "Light": Photons (X-rays), Ultrasound, Radiofrequency (RF) pulse.
  • Object: Attenuation of photons (X-rays), reflected Ultrasound, Resonance of RF pulse.
  • "Receptor": Film, Echography probe, Scanner, MRI antenna.
  • Signal Processing.
  • Visualization: Film, Screen (Radioscopy, Echography, Scanner, MRI).

Technical Evolution in Radiology

• 1895-1990: Continuous technological evolution with multiple Nobel Prizes.
  • 1895: First X-ray.
  • 1901: Wilhelm Conrad Rontgen Nobel Prize.
  • 1903: Marie Curie and Henri Becquerel Nobel Prize.
  • 1904: Lord Rayleigh Nobel Prize.
  • 1915: William Bragg Nobel Prize.
  • 1920: First arteriography.
  • 1921: Frederick Soddy Nobel Prize.
  • 1922: Francis William Aston Nobel Prize.
  • 1953: First Echography.
  • 1960: First Mammography.
  • 1970: First Scanner.
  • 1979: Godfrey N. Hounsfield Nobel Prize.
  • 1980: First MRI.
  • 1990: Digital Radiology.
  • 1992: Charpack Nobel Prize in physics.
  • 1995: Joseph Rotblat, Pugwash Conferences on Science and World Affairs Nobel Peace Prize.
• 1990-Present: Rapid acceleration.
  • 1994: Scanner with 2 detectors.
  • 1995: First imaging networks.
  • 2000: 3D imaging.
  • 2002: Digital Mammography, TEP (Positron Emission Tomography).
  • 2003: First PACS (Picture Archiving and Communication System), virtual endoscopy.
  • 2004: 4D imaging.
  • 2005: Functional MRI.
  • 2007: MRI at 7 Tesla.
  • 2008: Molecular Imaging, Generalization of archiving.
  • 2009: Scanner with 310 barrettes.
  • 2010: Region without film project.

Course Objectives

• Understand the physical principles of different radiological modalities: Conventional Radiology, Echography, Scanner, MRI.
• List the principles, indications, and contraindications of radiological exploration methods.
• Prescribe the most relevant radiological examination in the context of clinical and biological data.

Radiology Modules

• Thoracic Radiology
• Cardio-Vascular Radiology
• Uro-Genital Radiology
• Osteo-Articular Radiology
• Interventional Radiology
• Neuroradiology
• Basic Physics-Technique
• General Semiology
• Digestive Radiology

Basic Physics and Exploration Techniques in Radiology and Radiological Semiology

For Smart Radiologie Conventionnelle (Conventional Radiology)

Conventional Radiology

• Technique and physical principle.
• X-ray tube.
• Patient.
• Detector.

Production of X-rays

• Vacuum glass enclosure.
• Cathode and Anode.
• Accelerated electrons.
• Metallic target.
• Diaphragm.

X-ray Tube Scheme

• X-ray beam.
• Object.

Image Formation

• Quantity of radiation: mA (milliAmperes).
• Radiation hardness: kV (kiloVolts).
  • 30-80 kV: Low voltage, low penetrating rays.
  • 100-150 kV: High voltage, high penetrating rays.

X-ray Production

• X-ray tube formed by 2 electrodes:
  • Cathode: Tungsten filament.
  • Anode: Metal.
• Heating current of the cathode measured in milliAmperes ($mA$).
• Voltage applied between the 2 electrodes creates accelerated electron current.
• Electrons projected towards the anode and slowed by the atoms, causing energy emission in the form of photons (X-rays).

Object Traversal

• X-ray beam is directed towards the object.
• It undergoes variable absorption depending on:
  • Thickness of tissues traversed: greater thickness equals greater absorption.
  • Nature of tissues: specific absorption coefficient.
  • Energy of radiation: higher energy leads to lower absorption in tissues.

Image Formation (Continued)

• X Rays that traverse the object are collected by a receiver:
  • A photosensitive film contained in a cassette behind the object for analog radiography.
  • A detector sensitive to X-rays, providing direct information to a computer, which renders a final image - digital imaging, printed on film or viewed on a screen.

Basic Terminology in Conventional Radiology

• Based on the nature of traversed tissue → 4 fundamental tones:
  • Osseous (Bone).
  • Hydric (Water).
  • Adipose (Fat).
  • Aeric (Air).

Opacity

• Zone of high density (e.g., bone) → Absorption and attenuation of X-rays → White or radio-opaque image.
  • Bone: Calcium tone.
  • Muscle, liver, kidneys: Hydric tone.

Clarity

• Zone of lower density (e.g., lungs) → Little attenuation of X-rays → Dark or black image, or hyper-clarity.
  • Air: Aeric tone.

Application Domains of Conventional Radiology

• Urinary Radiology: Urethro-cystography retrograde (UCR).
• Thoracic Radiography: Pneumology, cardiology, resuscitation.
• Bone and Joint Radiography: Rheumatology, traumatology.
• Mammography: Senology.
• ASP (Abdomen without preparation).
• Arteriography: Opacification of blood vessels.
• Irradiating examination.

Echography = Ultrasonography (US) and Doppler Echography

• Monitor.
• Command console.
• Computer system that transforms the received signal into an image.
• Data recording system.
• Probes.

Echography Technique

• Interaction of ultrasound with the biological medium → Physical phenomena like absorption, attenuation, and diffusion.
• Reflected waves → Signal recorded in echography.
• Probe contains a piezoelectric ceramic.
• Electrical stimulation of the piezoelectric ceramic → Firing ultrasonic wave beams.
• Probe is both emitter and receiver.

Propagation Speed in Biological Tissues (Celerity)

• Water: 1480 m/s.
• Air: 340 m/s.
• Blood: 1566 m/s.
• Fat: 1460 m/s.
• Liver: 1560 m/s.
• Muscle: 1600 m/s.
• Skin: 1700 m/s.

Frequency/Wavelength/Exploration Depth Scale:

• 1 MHz: Abdomen (1.5 mm << 150 μm)
• 10 MHz: Neck, pediatrics, endocavitary (7.5-12 MHz) (150 μm << 75 μm)
• 20 MHz: Muscles/tendons, skin (20 MHz) (75 μm << 15 μm)
• 100 MHz: Eye (10 MHz), endovascular (30-50 MHz)

Echography: Strengths and Weaknesses

• Strengths: Inexpensive, accessible, repeatable, available, non-invasive (no irradiation, no injection), coupled with Doppler.
• Weaknesses: Operator-dependent, Patient-dependent (15% technical failure due to gas, obesity, lack of patient cooperation).

Gray Scale

• Image on screen, film, or photographic paper is rendered in grayscale.
  • Pure liquid: Echo-free or anechoic (bile, urine, cyst, ascites).
  • Calcifications: Bone is hyperechoic with posterior acoustic shadowing.
  • Soft tissues: Echogenic, with variable echogenicity (liver, spleen, kidney, tumor).

Main Echography Examinations

• Cardiac Echography
• Pleural Echography
• Breast Echography
• Testicular Echography
• Female Pelvic Echography
• Abdominal Echography
• Obstetrical Echography
• Urinary Tract Echography
• Thyroid Echography
• Musculoskeletal Echography
• Hepatic and Vesicular Echography
• Vesico-Prostatic Echography
• Digestive Echography
• Renal Echography

Doppler

• Technique coupled with echography using the same equipment.
• Study of moving structures: vessels and heart.
• Information is based on the frequency difference between the emitted and reflected ultrasound wave.
  • If the beam is reflected by blood elements moving towards the probe, its frequency will be higher.
  • If the beam is reflected by elements moving away from the probe, its frequency will be lower.
• Interest: Determines the direction of blood flow in vessels and calculates blood flow velocity.

Examples of Doppler Applications

• Echo-Doppler of the Portal Vein and Superior Mesenteric Vein (VSH).
• Renal Echo-Doppler.
• Carotid Echo-Doppler.
• Lower Limb Echo-Doppler.

Tomodensitometry (TDM) = Scanner

• Definition AS.

Scanner Basic Principle

• Patient lies on a table that moves through an annulus.
• X-ray tube rotates around the patient instead of being fixed.
• Annulus contains the X-ray emission tube and a series of detectors.

Scanner Function

• Continuous circular movement of the X-ray tube around the patient.
• Synchronized with the linear movement of the table at a constant speed.
• X-ray beam describes a helix around the patient, acquiring data continuously (continuous rotation scanner).
• Generates volumetric acquisition in a spiral form.
• Images in slices are reconstructed in all planes and manipulated by a computer.

Evolution of Scanner Generations

• Multidetector CT (MDCT).
• Scanners with multiple rows of detectors or barrettes (16, 32, 64, 128 detectors).
• Allow for acquisitions of 16, 32, 64, and 128 images per tube rotation.

Performance of Multi-Detector Scanners

• Rapid acquisition in a few seconds.
• Image quality, 2D and 3D reconstructions.
• New applications: Coroscanner (Cardiac CT).

Terminology

• Hyperdense lesion: Higher density compared to the reference organ.
• Hypodense lesion: Lower density.
• Isodense lesion: Identical density.

Hounsfield Units (HU) in Scanner

• Elementary information “u” is calculated by the computer for each point of the slice.
• Expressed in Hounsfield Units (HU).
• Value is assigned a color on a grayscale with two extremes:
  • White for bone (+1000 HU).
  • Black for air (-1000 HU).
  • Intermediate gray for water (0 HU).

Main CT Examinations

• Coro scanner
• URO-Scanner
• Osteo-articular CT
• Lower limb Angio-scanner
• Abdominal Angio-CT
• Cerebral CT
• Colo scanner
• Abdominal CT
• Entero Scanner
• Thoracic CT
• Thoracic Angio-CT
• Supra-aortic trunk Angio-scanner
• Upper limb Angio-scanner

CT Examinations (Examples)

• Cerebral Exploration
• Osteo-articular Exploration
• Abdomino-Pelvic Exploration
• Thoracic Exploration
• Aorta Angioscanner.

VRT:3D Reconstructions

• Virtual coloscopy
• Thoraco-Abdomino-Pelvic TDM

CT: Strengths and Weaknesses

• Strengths: Spatial resolution, rapid acquisition, Thoraco-Abdomino-Pelvic assessment.
• Weaknesses: Injection of contrast product, Renal insufficiency, severe allergy, acute cardiac insufficiency, irradiation.

Magnetic Resonance Imaging: MRI

MRI Principle

• Hydrogen atoms (human body) placed in an intense magnetic field (B0).
• Excited by a radiofrequency (RF) wave.
• During return to equilibrium, the emitted signal is collected, processed, and rendered as an image.
• Sequences are varied by altering the shape and duration of the exciting RF pulse and the moment when the signal is collected.

Hydrogen Atom/Proton

• Proton = abundant in the human body (Water > 60%).
• Proton is positively charged.
• Spins on its axis North-South.

Protons in the Body

• Oriented randomly.
• Not all spin together, so they are out of phase.
• Resultant magnetic moment is zero.

Patient in MRI Scanner

• Placed in a powerful magnet (tunnel), all protons align with the axis of the magnetic field, resulting in resting magnetization.
• Represented by a longitudinal magnetization vector.

MRI Antennas

• Antennas → RF waves → Stimulate protons.
• Energy supply to protons causes:
  • Tilting of proton direction relative to the magnet axis; Horizontal magnetization vector.
• Upon cessation of RF wave:
  • Protons return to the magnet axis and become dephased again.
  • Returning to their original state releases the supplied energy as a wave, a relaxation phenomenon captured by an antenna.
  • This wave is the MRI signal → Establishes the matrix image = protons cartography = MRI image.
• Antennas are both emitters and receivers.

Examples of MRI Antennas

• Head antenna.
• Whole body antenna.
• Knee antenna.

Diffusion MRI

• Based on the study of water molecule movements in tissues.
• When water molecule diffusion is limited, the diffusion signal is high, due to restriction of diffusion.
• Cerebral ischemia: reduced diffusion = increased intracellular water.

MRI: Advantages and Contraindications

• Advantages:
  • No radiation. Excellent soft tissue contrast.
  • Functional studies (functional MRI, diffusion, perfusion sequences).
• Contraindications:
  • Related to magnetic field: intracranial vascular clips, metallic heart valves, ocular metallic foreign bodies.
  • Devices with potentially disrupted function: pacemakers, cochlear implants, insulin pumps.

MRI Incidents

• Safety considerations important.

MRI Terminology

• Structures are defined by signal intensity on a given sequence.
  • Hyper-intense = Hyper-signal: Appears whiter than adjacent parenchyma.
  • Hypo-intense = Hypo-signal: Appears darker than adjacent parenchyma.
  • Iso-intense = Iso-signal: Signal is identical to adjacent parenchyma.

Main MRI Examinations

• MRI of the Urinary Tract
• Colo-MRI
• Entero-MRI
• Cardiac MRI
• Cerebral MRI
• Pelvic MRI
• Osteo-articular MRI
• Spinal MRI
• Abdominal MRI
• Lower Limb Angio-MRI
• Mammary MRI
• Biliary MRI (BILI-MRI)

Examples of MRI Examinations

• Cerebral MRI
• Spinal MRI
• Shoulder MRI
• Knee MRI
• BILI-MRI
• Hepatic MRI
• Cardiac MRI
• Breast MRI
• Pelvic MRI

Contrast Products

Contrast Product Injections

• Intravascular (Veins, Arteries) and Articular.
• Purpose: Visualize vessels and organs, guide procedures.

Types of Contrast Products

• Conventional radiology/CT: Iodinated contrast media → Increased density.
• MRI: Gadolinium chelates.

Risks of Contrast Products

• Allergy: potentially fatal shock or minor reactions.
• Renal Insufficiency: caution in patients with diabetes or myeloma; creatinine clearance > 50 ml/min is recommended, as well as hydration.

MRI Examinations

Angioscanner of Abdominal Aorta.(With and Without Contrast Injection).
*Hepatic MRI * (With and Without Contrast Injection).

Opacifications

• Articular
• Digestive
• Genito-Urinary

Examples

• Arthro-Scanner of the Knee
• Urethro-Cystography Rétrograde

Radioprotection

Comparing Sources of Radiation

• Air Travel 10 hours is equivalent to $0.04 mSv$
• Chest X-ray is equivalent to $0.1 mSv$
• Mammogram is equivalent to $0.4 mSv$
• Average background radiation (U.S., 1 year) is equivalent to $3 to 5 mSv$
• LDCT for lung cancer screening is equivalent to $1.4 mSv$
• Diagnostic CT is equivalent to $7 mSv$

Risks of X-rays

• The scanner delivers a dose 100 times greater than conventional radiology.
• X-rays are ionizing radiation, cumulative, and have secondary effects on tissues.
  • Genetic risk: gene mutation.
  • Effects on sensitive organs: skin, gonads, hematopoietic organs, crystalline lens.
  • Teratogenic effect during pregnancy: embryonic malformations.
  • Statistically significant risk of cancer from a cumulative dose of $100 mSv$ in humans: risk of leukemia after 5 years and solid tumor after 10 years.

Radioprotection Measures

• Local: Lead-lined walls and glass.
• Materials: Aprons, gloves, leaded screens.
• Reduce scattered radiation: Grids, diaphragms, cones.
• Reduce the number of radiological examinations and images.

Radioprotection Recommendations

• Avoid irradiation in pregnant women; prefer ultrasound and MRI.
• In young women, perform important abdominal explorations during the first part of the cycle.
• Protect gonads in children.

Radioprotection Principles

• Minimize radiation exposure.
  • Justify the examination: The indication must be necessary.
  • Always evaluate the Benefit-Risk of each scanner.
  • Optimize: use the lowest possible dose to obtain the necessary information. Limit exposure to 20-50 mSv per year.

Dose Calculation after a Scan

• Dose effective ($mSv$) = DLP x Conversion factor.
• DLP (Dose-Length Product): Total dose multiplied by the length of the scanned area, expressed in mGy·cm.
• The conversion factor is specific to the body region exposed. For example, for a thoracic scanner, this factor = $0.014 mSv/(mGy·cm)$.

Dose Calculation Example

• If a thoracic scanner yields a DLP of $400 mGy·cm$ and the conversion factor is $0.014 mSv/(mGy·cm)$, the effective dose would be:
  $Dose efficace = 400 ims 0.014 = 5.6 mSv$ Value recorded in the patient's file.

Interventional Radiology

Materials used

Vocaine (local anesthetic)

Semi-Automatic Biopsy

• Semi automatic: Controls progression of the acquisition window.
• Caliber: 1st biopsy 18 Gauge, 2nd Biopsy 14 Gauge
• 25mm, 5mm, 20mm needles indicated

Guidance of Interventional Radiology Procedures: Echography

• Liver Mass Biopsy.
• Breast Mass Biopsy.
• Hepatic Collection Drainage.

Guidance of Interventional Radiology Procedures: CT/TDM

Patient positioning: Decubitus ventral or lateral position

Examples of Interventional Radiology Procedures Under CT Guidance

• Bone Biopsy.
• Pancreas Mass Biopsy.
• Peritoneal Nodule Biopsy.
• Lung Nodule Biopsy.
• Liver Abscess Drainage.
• Retroperitoneal Mass Biopsy.

Therapeutic Interventional Radiology

• Thermo-ablation.
• Chemo-Embolization.

Conclusion

• Clinic Prescriber interacting with;
• Radiologist.

Patient Radiological Assessment

• Physician: Clinical examination-Biology.
• Irradiating Examination: X-rays (Conventional Radiology, TDM).
• Non-irradiating: Echography, MRI.

Radiological Examination Prescription

• Date of consultation, patient identity.
• Requested examination, region to explore.
• Clinical information, relevant patient history.
• Clinical signs, results of additional examinations.
• Objectives of the examination: Suspected diagnosis.