Radionuclides and Imaging Techniques Quiz

Medical Imaging Modalities

• Medical imaging modalities include MRI, Radio frequency waves, Computed Tomography, X-rays, Advanced X-ray machines, Simple X-ray, Positron Emission Tomography (PET) Scan, Radioactive drug, Imaging Gamma rays emitted from the body, Ultrasound, and SPECT scan.

X-rays

• X-rays produce a shadow image with gradation.
• X-rays can be either absorbed or scattered by tissue.
• X-ray system has four groups: X-ray tube, Cathode, and anode, which generate electrons, and Film Screen Detection.
• Radiographic film is used to complete the image.
• Phosphor plates absorb X-rays, and electrons sit in an energy trap within the phosphorous.
• Once a laser is shone over the plate, light is emitted, and an image is received.
• CCD camera and readout of pixels are used to detect X-rays.
• Flat panel Detectors are used for direct detection of X-rays.

Image Reconstruction

• Image reconstruction is necessary when the detector is far away from the subject or scanner.
• The detector receives the X-ray at points and stretches them out into stripes.
• Electrons bounce off the cathode and slam into the anode at high speed, producing X-rays.

Detector/Sensor Tissue Interaction

• The amount of X-rays absorbed or scattered by tissue depends on the density and chemical composition of the tissue.
• The intensity of the X-ray beam through the tissue can be calculated using Beer's Law: I = Io*e^(-μ)*x.
• The X-ray knocks off electrons on the atoms of the tissue, emitting light (Photoelectric effect) and Compton scatter.
• Higher energy results in more scatter in a single direction, whereas lower energy results in more averaged scatter.
• The highest resolution photos are obtained through the Photoelectric effect.

Mammography

• Mammography is a high-resolution imaging procedure involving X-rays.
• It requires less X-rays and power to get a clear reading.
• Spreading the tissue out by compressing it reduces scatter and enables easy visualization of irregularities.
• Microcalcifications occur when the tissue's micro environment changes, and fibrous tissue begins to deposit calcium.
• A palpable mass in a breast cannot be easily viewed in a mammogram and requires ultrasound or another imaging technique.

CT Scans

• CT scans use X-rays in parallel and project from a single X-ray source with multiple X-ray detectors.
• The detectors rotate around the patient, collecting many small projections to create slices of the inside of the body.
• CT scans usually use much more radiation than normal X-rays (Dental X-rays are usually the lowest dose).

Nuclear Emission Imaging

• Nuclear Emission Imaging involves injecting a radioactive tracer into the patient, which emits energy that the PET scan can detect.
• The idea is to scan the patient after injecting the tracer into the body and accumulate in regions of interest, such as a tumor.
• Many scanners are built into each other, making it convenient to combine CT and PET scans.

PET Scans

• PET scans use a radioactive tracer that is injected into the patient.
• The tracer emits energy that the PET scan can detect.
• The idea is to scan the patient after injecting the tracer into the body and accumulate in regions of interest, such as a tumor.
• Tracer production utilizes Cyclotrons, a particle accelerator, and the cost is upwards of $6,000 per PET scan or tracer injection.
• The half-life of the tracer is incredibly fast, and they must be used the same day they are made in order to be useful.

SPECT Scan

• SPECT scan is similar to PET scan but is often used instead as it is much less expensive.

MRI

• MRI is founded on the principles of Nuclear Magnetic Resonance (NMR).
• It localizes NMR signals to provide actual images.
• The MRI works by aligning all the protons in the body along a very powerful magnetic field.
• These protons in the body align into essentially tiny radio antennas that allow the generation of RF waves.
• Faraday's law tells us that if we change a magnetic field or emit a magnetic field through a wire, it will begin producing current.
• The nuclei are similar to the coil, and nuclei can be thought of as little bar magnets.

History

• In 1895, Roentgen discovered the use of X-rays to his own detriment (died from radiation exposure).
• In 1896, a doctor first used an X-ray to treat a young Eddie Maccarthy after a skating accident.
• Within a year, 1,000 new papers were published on X-rays.
• In 1955, Alan Cormack devised the mathematics behind the CT scan method.
• In 1960, a engineer from a record company created a CT scanner in secret.
• Later, Hounsfield and Cormack received the Nobel Prize.

Test your knowledge on radionuclides, radionuclide generators, imaging techniques like PET and SPECT scans, and the use of radioactive atoms in medical imaging. Learn about how Flourodeoxyglucose is used in imaging highly metabolic cells such as tumors.