8. Imagenología Sin Radiación - Dr. Nibaldo Venegas

Introduction to Ultrasound and Its Applications

Overview of the Class

• The class focuses on ultrasound (also known as ultrasonography) and magnetic resonance imaging (MRI), with approximately 75% dedicated to ultrasound.

• Clarification is made regarding the term "ecotomografía," which refers to older generation ultrasound technology, while "ecografía" or "ultrasonido" are preferred terms today.

Misconceptions About Ultrasound

• It is a common misconception that ultrasound is only used for viewing babies in gynecology; however, its applications have expanded significantly.

• Ultrasound can evaluate any part of the body where a probe can be placed, demonstrating its versatility beyond traditional uses.

Ultrasound Equipment and Probes

Types of Probes

• There are various types of ultrasound probes: linear, convex, endoluminal, and sectorial probes used primarily for cardiac studies.

• Linear probes provide high resolution for superficial structures but less depth penetration (up to 6 cm), while convex probes offer better depth resolution (up to 20 cm).

Frequency Ranges

• Convex probes typically operate at lower frequencies (2–5 MHz), whereas linear probes can reach higher frequencies (up to 17 MHz), allowing for detailed imaging of superficial structures like joints and muscles.

• The choice of probe affects image quality and application in clinical practice; linear transducers are likened to an extension of the stethoscope in modern medicine.

How Ultrasound Imaging Works

Principles Behind Image Generation

• The concept behind ultrasound imaging parallels sonar technology used by submarines; sound waves emitted from a transducer bounce off objects and return data about their distance.

• Natural examples include echolocation in bats and dolphins using ultrasonic waves to navigate and locate prey effectively.

Technical Components

• A piezoelectric crystal within the transducer emits ultrasonic waves that interact with internal body structures, allowing real-time measurement of distance, size, shape, etc., leading to image formation on screen.

Modes of Ultrasound Imaging

Different Imaging Modes

• The most commonly used mode is B-mode (brightness mode), which produces grayscale images; M-mode captures moving images represented in color or curves. Other modes exist but are less relevant in general radiology contexts.

Common Applications

Ecografía: Evaluación de Articulaciones y Órganos

Ecografía de Hombro

• La ecografía de hombro es una de las más solicitadas, junto con la ecografía abdominal, para evaluar articulaciones.

• Este estudio es económico y poco invasivo, ideal como método de screening inicial para el abdomen. Su mayor utilidad radica en la evaluación de la vesícula biliar, considerada el "Gold estándar" en imágenes.

• La ecografía abdominal permite visualizar órganos sólidos como hígado, páncreas y riñones, así como estructuras huecas que no contengan aire. Sin embargo, el meteorismo puede limitar su efectividad en el tubo digestivo.

• Para una evaluación óptima de la vesícula biliar, se recomienda que el paciente esté en ayunas para obtener imágenes claras del espesor de las paredes y estructuras internas.

• Un ejemplo visual incluye un cálculo en ecografía que muestra una imagen blanca con sombra acústica posterior; esto contrasta con barro biliar que no debe confundirse con cálculos.

Evaluación Clínica a través de Ecografías

• Los cálculos biliares son visibles por ecografía pero pueden ser difíciles de detectar por escáner debido a su composición.

• Se presentan ejemplos clínicos donde se observa colelitiasis (cálculo en vesícula no complicada) y colecistitis (cálculo impactado).

Ecografía del Manguito Rotador

• La ecografía del hombro también se utiliza para evaluar tendones del manguito rotador y el tendón largo del bíceps braquial.

• El transductor se coloca transversalmente sobre la cabeza del húmero para observar los tendones; esto incluye evaluaciones longitudinales para ver toda la extensión del tendón bicipital.

Anatomía y Evaluación Estructural

• Se describe cómo estudiar el tendón supraespinoso dentro del manguito rotador; este tiene características anatómicas específicas que facilitan su identificación durante la ecografía.

• El redondo menor es más difícil de evaluar debido a su ubicación posterior. Se utiliza una analogía vehicular para describir cómo deben estar intactos los "neumáticos" (los tendones).

Diagnóstico por Imágenes

• Al hablar sobre el manguito rotador, se menciona que debe haber homogeneidad en el grosor de los tendones al ser evaluados por ecografía.

• Un ejemplo práctico muestra un tendón roto donde hay disrupción visible tanto en cortes transversales como longitudinales.

Understanding Doppler Ultrasound and Its Applications

Overview of Biceps Tendon Imaging

• An example is presented showing a normal biceps tendon on the left and a thickened tendon with surrounding fluid on the right, indicating potential bicipital tendinitis.

Introduction to Doppler Effect

• The Doppler effect, discovered by Austrian physicist Christian Doppler, is explained as a method for measuring speed using sound waves.

• Analogies are provided: police radar measures vehicle speed via ultrasound waves; the changing sound of an approaching or receding ambulance illustrates the effect in everyday life.

Historical Context of the Doppler Effect

• Christian Doppler discovered this phenomenon in 1842, not foreseeing its extensive applications beyond medicine, including fields like mining.

Types of Doppler Studies

• In medical imaging, "Doppler" can refer to various studies (arterial, venous), complicating radiologists' interpretations when only "Doppler study" is requested.

• Key studies include evaluations of upper/lower extremities and specific organs such as renal and portal systems.

Specific Applications of Doppler Ultrasound

• Lower extremity studies can be arterial or venous; clarity in medical orders is crucial to avoid lengthy examinations.

• Carotid and vertebral Dopplers assess vascular structures in patients with cerebrovascular accidents or transient ischemic attacks.

Evaluating Vascular Health

• The carotid study focuses on identifying stable (calcium-rich) versus unstable (lipid-rich) plaques that pose risks for vascular accidents.

• Plaque location within arteries is critical; areas with turbulent flow are more prone to plaque formation.

Practical Aspects of Conducting a Study

Evaluation of Vascular Structures and Interventions

Assessment of the Vertebral Artery

• The posterior circuit is evaluated through the vertebral artery, which helps characterize plaques and determine their potential impact on cerebral irrigation.

• A significant plaque in the internal carotid artery can lead to over 70% stenosis, indicating a critical compromise in blood flow.

Clinical Implications of Doppler Studies

• Patients with significant stenosis may be candidates for surgical interventions like endarterectomy, where an expander is placed in the affected artery.

• Doppler studies are commonly requested for evaluating venous conditions such as thrombosis or insufficiency; urgent evaluations focus on thrombosis.

Procedure for Venous Evaluation

• The study begins by checking vascular structure permeability; normal flow is indicated by color changes during ultrasound imaging.

• Compression tests reveal thrombus presence: compressible veins indicate normal flow, while non-compressible veins suggest thrombosis.

Applications in Neonatology and Other Fields

• Ultrasound is also used in neonatology to assess brain health via transfontanelar methods due to its low invasiveness.

• It aids in diagnosing hip dysplasia, measuring hematomas, and guiding procedures like central line placements or fluid drainage.

Advancements in Imaging Technology

• High-resolution imaging has improved significantly with advancements in transducer technology, allowing better definition of structures.

• Resolution refers to the ability to distinguish between different tissue types; modern equipment can discern structures smaller than 3 mm.

Understanding MRI Technology

• Magnetic Resonance Imaging (MRI), previously known as nuclear magnetic resonance (NMR), uses powerful magnets and high-frequency coils for imaging.

Understanding Magnetic Resonance Imaging (MRI)

The Importance of Faraday Cages in MRI

• MRI machines require a Faraday cage to shield against the powerful magnetic fields generated, which can interfere with nearby structures.

• The use of thick concrete and additional shielding systems is essential to prevent magnetic interference from affecting surrounding areas.

Types of MRI Studies

• Different types of MRIs are used for various organs; for example, hepatic resonance focuses on the liver while biliary resonance targets the bile duct system.

• Commonly performed MRIs include knee, pelvic, and breast scans. Fetal MRI is also utilized during pregnancy due to its safety profile.

Patient Considerations and Contraindications

• Certain patients may face challenges such as claustrophobia or anxiety during an MRI scan; sedation may be necessary in some cases.

• Absolute contraindications include older prosthetics or any external metallic objects that could move during the exam.

Fundamental Principles of MRI

• The basis of MRI lies in atomic structure; atoms consist of protons and neutrons with electrons orbiting around them, creating a magnetic field.

• Hydrogen atoms, prevalent in the human body, act like small magnets due to their unique spin properties.

Image Generation Techniques

• The disordered spin movement of hydrogen atoms is manipulated by the MRI machine to generate images through ordered spins.

• Two primary sequences are used: T1-weighted and T2-weighted imaging. Diffusion sequences are particularly useful for detecting water movement in brain protocols related to stroke.

Case Study: Knee Injury Diagnosis

• A case study illustrates how an athlete's knee injury was diagnosed using an MRI after normal X-rays and ultrasounds failed to reveal issues.

• The mechanism involved hyperextension leading to disruption in anterior cruciate ligament fibers, confirmed through specific imaging sequences showing bone edema.

Conclusion and Acknowledgments