Comprehensive notes on Radiology Modalities, Planes, and Terminology

Radiology Department Overview

• Radiology is the hospital department responsible for imaging and uses various modalities: radiography (X-ray), ultrasound, CAT scan (CT), MRI, nuclear medicine, mammo (mammography), and PET scans.
• X-ray is also referred to as radiography; radiology encompasses any imaging modality that uses radiation (CAT scan, nuclear medicine, mammo, special procedures) while ultrasound and MRI do not use radiation.
• In some hospitals, ultrasound and MRI sit within radiology; in others, MRI may be a separate department, but for this course they’re treated as imaging modalities within radiology.
• Special procedures in some hospitals have been renamed to interventional radiology.
• PET scan is a combination of nuclear medicine and CT imaging and is used mainly in oncology.
• Learning the terminology and department structure helps you integrate into the healthcare team and reduces feelings of isolation in a hospital setting.

Imaging Modalities and Key Concepts

• Modality: a distinct imaging technique (e.g., X-ray, ultrasound, CT, MRI, nuclear medicine).
• Ultrasound and MRI do not use ionizing radiation; CT, X-ray, nuclear medicine do.
• Common imaging modalities and their primary radiation association:
  • X-ray (radiography): uses X-ray radiation; excellent for bones; limited for soft tissue and overlapping structures.
  • Ultrasound (sonography): uses high-frequency sound waves; no radiation; great for soft tissue and vascular imaging but limited in bone and air-filled structures.
  • CAT scan (CT): uses X-ray radiation; excellent for overlapping structures and 3D/sectional anatomy; uses Hounsfield units for tissue characterization.
  • MRI: uses strong magnetic field; no ionizing radiation; superior soft tissue contrast; slower and magnet safety critical.
  • Nuclear medicine: uses radioactive tracers; functional imaging; includes PET as a hybrid modality with CT.
• PET scan: combination of nuclear medicine and CT; used to detect cancer spread and treatment response.
• Interventional radiology: term used in some hospitals for “special procedures” performed by radiology physicians.
• Terminology summary will recur: axial, sagittal, coronal planes; and ultrasound-specific terms like long and trans.

Radiography (X-ray)

• X-ray is the simplest and most common radiologic study; often the first line for imaging bones and joints.
• Strengths: excellent bone imaging; quick and widely available.
• Limitations: soft tissue detail is poor; overlapping structures obscure details; air appears black and bone appears white on X-ray film.
• Chest X-ray: most common X-ray in hospitals; view the lungs (air-filled, appear black) and heart silhouette (the heart shadow).
• Diaphragm anatomy and role:
  • Diaphragm separates thoracic and abdominal cavities; deep breathing lowers the diaphragm, pushing abdominal organs downward to help ultrasound liver/spleen visualization and gas pattern evaluation.
• Soft tissue visibility: X-ray is poor for detailing soft tissues such as nerves, blood vessels, ligaments, and fat; some soft-tissue detail is possible but limited.
• Air appearance: air is black on X-ray; air surrounding a hand example appears black around the bones.
• Key features on a chest X-ray:
  • Lungs: black due to air.
  • Heart silhouette: central white area; does not reveal chamber details; can indicate enlargement.
• Radiologist vs radiographer/technologist:
  • Radiologist: physician who reads/interprets X-ray films.
  • Radiographer (X-ray tech): performs the imaging and positioning.
  • Ultrasound tech (sonographer): performs ultrasound imaging.
• Common X-ray terms and views:
  • KUB: kidneys, ureters, bladder. Abdominal X-ray; often includes upright and supine views.
  • Lead markers: radiology films marked with left/right indicators and markers for patient position; initials indicate the technologist who performed the study.
  • BB markers in the abdominal film indicate patient position (standing vs. lying down).
• Abdominal X-ray (KUB) usefulness:
  • Gas patterns reveal bowel obstruction or ileus.
  • Calcifications such as kidney stones (calcium-containing) appear white.
• X-ray equipment basics:
  • Table (X-ray table), bucky assembly (holds the film), radiation source and detector behind shielding.
  • Fluoroscopy: similar X-ray source but used for real-time moving images; camera-like output.
• Safety and radiation protection:
  • Always stand behind a lead shield or behind leaded glass and walls when the X-ray beam is active.
  • Technologists and patients use protective shielding; the beam is restricted to the area of interest.
  • Film badges are not typically provided in ultrasound training, due to non-radiation exposure; in clinical radiography training or practice, badges are used for monitoring exposure.
• In-clinic practice and downtime:
  • If you have downtime, you should avoid entering radiation areas; observe and learn but do not participate in radiating.

Computed Tomography (CT/CAT Scan)

• CT uses ionizing radiation and provides cross-sectional images (slices) of the body.
• The CT scanner is donut-shaped; patients lie on a bed that moves through the ring while X-ray tubes rotate around them; the image is reconstructed into axial slices.
• Slice thickness and planarity:
  • CT slices are typically thinner than standard radiographs, enabling detailed evaluation of small structures.
• Hounsfield units (HU): the CT-specific tissue density scale used to characterize tissue on CT images.
  • Scale range:
    $-1000 \le HU \le +1000$
  • Common reference values:
  • Air: $HU \approx -1000$
  • Water: $HU = 0$
  • Fat: negative HU values (typical fat around -50 to -100, depending on tissue)
  • Soft tissue: positive HU values (roughly 20–60, varies with tissue type)
  • Bone: typically $HU > 1000$ (often well above 1000, depending on density)
  • The radiologist or CT technologist can click on a lesion; the HU value helps characterize whether a lesion is solid, cystic, fatty, hemorrhagic, etc.
• CT workflow concepts:
  • Slices are evaluated individually (sectional anatomy).
  • CT is fast and widely used in trauma to rapidly assess injuries (head, chest, abdomen).
  • Multiplanar reconstructions (MPR) allow viewing in sagittal and coronal planes in addition to axial.
• Comparison with ultrasound:
  • CT provides excellent bone and overlapping-structure visualization with HU-based tissue characterization.
  • Ultrasound excels at soft-tissue contrast without radiation and can further characterize lesions identified on CT, except it cannot image through bone like the skull effectively.

Magnetic Resonance Imaging (MRI)

• MRI uses a strong magnetic field and radiofrequency pulses; no ionizing radiation.
• Safety: MRI involves a powerful magnet; metal and ferromagnetic objects must be removed (badges, watches, jewelry, metal hair accessories, etc.); doors to MRI areas are typically secured and access is controlled; staff escort is required.
• Structural differences: MRI provides superior soft-tissue contrast and is slower than CT; patient must remain still to avoid motion artifacts.
• MRI environment and patient experience:
  • The MRI bore is a long tunnel; many patients experience claustrophobia; music or ear protection is commonly provided.
  • We often describe MRI sequences as T1-weighted and T2-weighted imaging (weighting terminology). These provide different tissue contrast to help distinguish anatomy and pathology.
  • Common safety note: MRI rooms are designed to minimize ferromagnetic risk; anything containing metal becomes a projectile if pulled into the magnet.
• MRI anatomy and planes:
  • The same true planes apply: axial (transverse), sagittal, coronal; midsagittal plane is the midline sagittal cut.
  • T1 vs T2 weighting differences (not deeply covered in this session, but conceptually important).
• MRI vs ultrasound brain imaging in infants:
  • In babies, the anterior fontanelle (soft spot) provides a natural acoustic window to view the brain with ultrasound.
  • Transcranial Doppler ultrasound can assess blood flow in brain vessels; ultrasound is particularly valuable for neonatal brain imaging due to fontanelles.

Ultrasound (Sonography)

• Ultrasound uses high-frequency sound waves; no ionizing radiation.
• Modes and practicality:
  • Ultrasound probes (transducers) emit and receive sound waves; images are formed in real-time and can be manipulated to view structures from multiple angles.
  • Ultrasound probes can be oriented to image in different planes; ultrasound commonly uses long (sagittal or coronal) and trans (axial) designations, though long is not a true anatomical plane.
• Planes and labeling in ultrasound:
  • In ultrasound practice, long = sagittal or coronal views when imaging a structure from the side or along the length, and trans = axial views.
  • The three true planes (axial, sagittal, coronal) are used primarily in CT/MRI; ultrasound uses the ultrasound-specific terminology of long and trans for convenience.
• Strengths and limits:
  • Excellent for soft tissues, vessels, and real-time assessment; real-time motion and blood flow imaging (Doppler) are common.
  • Poor visibility for bone (scattered/reflected by bone) and lungs due to air.
• Organ-specific notes:
  • Abdomen: organ visualization such as liver and spleen; the cosophrenic angles can help assess fluid or ascites; gas patterns in bowel are visible.
  • Heart: echocardiography (ultrasound of the heart) and heart chamber visualization; can perform detailed cardiac assessment (echo).
  • Lungs: ultrasound limited by air; some lung pathology can be inferred in limited regions.
• Baby/OB ultrasound:
  • OB ultrasound is a major application, including fetal imaging and monitoring.
  • Pediatric imaging includes neonatal brain ultrasound through fontanelles; brain anatomy can be visualized more easily in infants than adults.
• Operator role and interpretation:
  • Ultrasound technologists (sonographers) are responsible for acquiring images, measuring structures, and communicating findings to radiologists.
  • They must evaluate whether organs are normal or abnormal and explain findings to the radiologist; unlike some other modalities, ultrasound requires the operator to actively assess and interpret findings during the exam.
• Equipment and general workflow:
  • Ultrasound machines vary by brand but share common functionality; button layouts differ by brand but core functions are similar.
  • The ultrasound exam does not involve radiation; the operator can manipulate the probe to obtain diverse views and angles.

Nuclear Medicine and PET Scans

• Nuclear medicine imaging uses radioactive tracers to evaluate physiological processes; it often highlights functional activity rather than solely anatomical structure.
• PET (Positron Emission Tomography): combines nuclear medicine with CT imaging for metabolic/functional assessment across the whole body; commonly used in cancer staging and treatment monitoring.
• Nuclear medicine images are often described as hot spots (areas of uptake) or cold spots (areas of low uptake); interpretation requires specialized training.

Planes and Anatomical Orientation (Foundational Terms)

• Anatomical position: standing upright with feet together, arms at the sides and palms forward; serves as a reference position.
• True body planes:
  • Axial (also called transverse): divides body into superior (top) and inferior (bottom) parts.
  • Sagittal: divides body into left and right sides; midsagittal is the midline plane.
  • Coronal (frontal): divides body into anterior (front) and posterior (back) sections.
• Planes terminology nuances:
  • Long: ultrasound shorthand covering sagittal and coronal planes when imaging; not a true plane, just a labeling convention.
  • Trans: ultrasound shorthand for axial plane (transverse) imaging.
• Additional directional terms:
  • Cephalic / Caudal: towards the head / towards the tail; equivalent to superior / inferior for humans.
  • Superior (cephalic) / Inferior (caudal): toward head / toward feet.
  • Proximal / Distal: nearer to / farther from the attachment point (e.g., shoulder vs. elbow).
  • Medial / Lateral: toward the midline of the body / away from the midline.
  • Anterior / Posterior: toward the front / toward the back.
• Abbreviations and usage examples:
  • Proximal to distal relationship example: elbow is distal to shoulder; knee is distal to hip; head is proximal to the feet along the limb.
  • When describing a structure within an organ (e.g., liver), you can refer to lobes as lateral/medial relative to the liver as a whole.
• Ipsilateral vs Contralateral:
  • Ipsilateral: same side as reference point.
  • Contralateral: opposite side relative to the reference point (e.g., right-sided head injury with left brain injury is contralateral).

Practical Imaging Workflow and Safety Notes

• CT vs MRI vs X-ray safety:
  • X-ray and CT involve radiation; MRI involves no radiation but uses a powerful magnet.
  • In X-ray and CT rooms, stand behind shielding; use protective equipment; hold breath instructions are common during imaging to reduce motion and improve image quality.
  • MRI safety: remove all metal items and jewelry; escort required; no ferromagnetic items; proper patient screening is essential.
• Breaks, downtime, and clinical expectations:
  • When observing clinicals, you should not participate in radiating patients; you may observe departments like CT, X-ray, or MRI to gain familiarity without exposure to radiation.
  • During downtime, you can gain exposure by observing, but you cannot hold patients or operate equipment that would involve radiation.
• Practical notes for ultrasound practice:
  • You will be responsible for acquiring and interpreting ultrasound images, measuring structures, and communicating findings to the radiologist.
  • You must justify findings and determine if organs appear normal or abnormal and explain reasoning.
  • You will apply knowledge of planes (long vs trans) and anatomical orientation to describe findings clearly in reports.

Quick Reference: Key Acronyms and Terms

• HU: Hounsfield Units, CT tissue density scale
• KUB: kidneys, ureters, bladder (abdomen X-ray view)
• PET: Positron Emission Tomography (nuclear medicine + CT)
• MRI: Magnetic Resonance Imaging
• CT/CAT: Computed Tomography
• US/Ultrasound: sonography
• ROI: region of interest (conceptual, not elaborated here)
• L/R markers: left and right film markers indicating patient orientation
• MPR: multiplanar reconstruction (CT capability)
• DAG: not used here; placeholder for context

Study Tips and Takeaways

• Know the strengths and limitations of each modality:
  • X-ray: quick, bone-focused, limited soft tissue detail, air contrasts well.
  • CT: fast, excellent for bone and overlapping structures; uses HU for tissue characterization.
  • MRI: superior soft tissue contrast; no radiation; slower; magnet safety is critical.
  • Ultrasound: real-time, great for soft tissue and vascular imaging; no radiation; operator-dependent.
  • Nuclear medicine/PET: functional imaging; whole-body assessment for cancer.
• Master anatomical planes and directional terms; practice labeling axial, sagittal, and coronal views; understand midsagittal symmetry.
• Learn to describe findings with appropriate qualifiers (proximal/distal, medial/lateral, anterior/posterior, cephalic/caudal, ipsilateral/contralateral).
• Understand the workflow: image acquisition, interpretation by radiologist, and reporting to the physician; ultrasound requires active measurement and interpretation during the exam.
• Practice with common cases: chest X-ray (lung fields, heart silhouette), abdominal X-ray (gas patterns, KUB), head CT/MRI (axial slices), abdominal ultrasound (liver, kidneys, gallbladder), fetal OB ultrasound, and neonatal brain ultrasound through fontanelles.