Diagnostic Imaging Definitions
Radiograph:
A radiograph (also known commonly as plain film or x-ray) is an image obtained by shining high energy light or x-rays through the body to a detector which may either be photographic film or a photo-sensitive plate in newer digital image systems. The body absorbs different amounts of radiation depending on the density of the tissue. Dense tissues such as bone absorb more radiation and appear light, and less dense tissues such as lung absorb less radiation and appear dark. The image obtained of a body part therefore represents a shadowgram. Disease states often alter the absorption of a given tissue. For instance, pneumonia increases the density of lung and results in a lighter shadow on the radiograph corresponding to the area of infection. Conversely a fracture decreases the absorption of bone and is perceived as a dark line at the fracture site.
Conventional Tomograms:
Conventional tomograms (also known as plain film tomograms) are radiographs, which are used to evaluate a specific plane within the body by blurring out tissues above and below the plane of interest. The x-ray source and detector are moved about a focal plane centered in the body. The tissues above and below the plane of interest are blurred, and the focal plane remains sharp. This technique may be useful in determining fracture healing, evaluation of pulmonary nodules (though this has largely been replaced by Computed Tomography, see below), evaluating the kidneys in excretory urography, and evaluating the integrity of spinal fusion.
Computed Tomography:
Computed Tomography (also known as CAT Scan, Computed Axial Tomography) is a technical advance over Conventional Tomography. An X-ray source and detector are moved about a focal plane in the body, as in Conventional Tomography, but a computer is used to generate an accurate cross-sectional image of the body. This powerful technique is used to evaluate pathology throughout the body. Administration of intravenous iodinated contrast aids in the evaluation of solid organ disease, for example, metastatic lesions within the liver. Iodinated contrast may also be injected into the joints in the detection of ligament tears or other joint abnormalities.
Fluoroscopy:
In this technique a portion of the body is exposed to a continuous beam of x-ray radiation to generate a movie-like image which is viewed on a TV monitor. This technique is helpful for the evaluation of motion of bones within joints, swallowing and gastro-intestinal studies, and evaluation of lung and diaphragm abnormalities. Fluoroscopy is used for accurate placement of needles for interventional procedures.
Ultrasound:
This technique utilizes sound waves to produce images. A transducer is placed on the skin, which generates high frequency sound. The sound penetrates the body and is returned as echoes at the interface of anatomic structures or areas of pathology. The echoes are received by the transducer and are combined to form an image. Ultrasound is excellent for evaluating the liver, gallbladder and kidneys, fetal development, and female pelvic disease.
Arthrogram:
Arthrograms are used to evaluate the internal characteristics of the joints. A needle is introduced into a joint, and iodinated contrast is injected. Radiographs are obtained. Arthrograms may detect ligament tears or cartilage abnormalities.
Myelogram:
Myelography is utilized to evaluate for disk pathology and degenerative changes of the spine. A needle is introduced into the spinal canal under fluoroscopic guidance and iodinated contrast is injected into the thecal sac, which contains the nerve roots. Radiographs are then obtained. The patient may go on to CT imaging for a more precise evaluation of the disk and spinal canal. Please see CT myleogram.
Diskogram:
A diskogram is utilized to evaluate the internal architecture of a disk and to determine whether or not an individual disk is responsible for a patient’s symptoms. A needle is introduced into an intervertebral disk under fluoroscopic guidance and iodinated contrast is injected into the disk. The patient is questioned as to whether the increased pressure within the disk caused by the contrast generates pain similar to the patient’s usual symptoms. Radiographs are then obtained. The patient may then go on to CT imaging for a more precise evaluation of the disk and spinal canal.
CT Arthrogram:
A CT arthrogram is similar to the plain film arthrogram discussed earlier. A needle is introduced into a joint and iodinated contrast is injected, outlining the joint capsule, ligaments, and articular surfaces. A CT is then obtained. Ligament tears and cartilage abnormalities are well-demonstrated with this technique.
MR Arthrogram:
MR arthrography is useful for detection of ligament tears and cartilage abnormalities. A needle is introduced into the joints of interest under fluoroscopic guidance. Contrast material visible on MR imaging is injected, and the patient is then sent to the MR scanner to obtain images. Cartilage abnormalities, tendon tears, and ligament tears are well demonstrated with this technique.
Magnetic Resonance Imaging:
MRI is a powerful imaging technique which exploits the magnetic properties of hydrogen atoms within the body. This imaging technique uses magnetic fields and radio waves and does not employ ionizing radiation. MR is extremely helpful in evaluation of disorders of the central nervous system and musculoskeletal system as well as for abdominal and chest imaging.
Nuclear Medicine Imaging:
Nuclear medicine imaging visualizes the distribution and uptake of radioactively-labeled molecules called radiopharmaceuticals. Different radiopharmaceuticals are used depending on the body part or disease state being evaluated. A radiopharmaceutical is typically injected intravenously, and after allowing an appropriate amount of time for target organ absorption, the patient is imaged using a gamma camera, which detects the gamma radiation similar to x-rays emitted by the radiopharmaceutical. Although the spatial resolution is limited relative to radiographic imaging techniques, this modality is unique in its ability to characterize the function of tissues. For instance, radioactive iodine is used to determine the ability of the thyroid gland to absorb iodine and also to evaluate increased or decreased function within a thyroid nodule, a characteristic helpful in assessing whether or not a thyroid nodule is potentially malignant. One of the most frequent uses of nuclear medicine is to evaluate skeletal abnormalities utilizing a bone scan. Bone scan radiopharmaceuticals are taken up by osteoid, a compound present in newly forming bone. Many abnormalities of bone are associated with increased osteoid production, including fractures, infection, and tumors, and will show up as “hot spots” on a bone scan.
Factors Affecting the Quality of the MRI Scan:
There are several reasons for poor quality images with MR imaging. Perhaps the most common problem encountered is motion artifact, which may due to patient pain, claustrophobia, anxiety, or non-compliance. Obesity may result in poor scans secondary to decreased imaging signal and relatively increased image noise. The quality of a scan may also be affected by the intrinsic imaging abilities of a scanner. Low magnetic field strength may result in decreased resolution and image contrast. Metal distorts magnetic fields and may result in loss of imaging information adjacent to metallic objects. For instance, anatomic detail around spinal fusion hardware may be obscured, and similar areas of signal loss may be noted next to joint replacements, bullet fragments, or surgical clips.
MR Surface Coils:
The quality of an MR image improves with increasing strength of the imaging signal. Signal increases the closer an MR receiving antenna or coil is located to the body part imaged. Therefore, surface coils, which lie on the patient’s skin, are extremely useful for looking at joints and other small anatomic regions requiring high-resolution imaging.
Contrast-Enhanced MRI:
The use of intravenous gadolinium chelate contrast has been widely employed for specific applications. Contrast-enhanced MRI is useful for determining scar versus recurring disk protrusion or bulge in the post-operative spine. Contrast-enhanced imaging of the central nervous system is especially helpful in the evaluation of infection, white matter disease, and neoplastic disease. Contrast may be used in body imaging for tumor evaluation. Certain MR angiography techniques employ intravenous contrast administration. Dilute gadolinium contrast is used for MR arthrography.
Contrast Enhanced CT:
Iodinated intravenous contrast is often used in body CT. It is especially helpful in the evaluation of neoplastic disease of the abdomen. Intravenous contrast-enhanced chest CT is useful for the evaluation of mediastinal or hilar adenopathy. Iodinated contrast is generally safe but in rare incidences may cause an allergic type reaction, which may range from hives to life-threatening anaphylaxis. Life-threatening reactions are extremely rare. Reactions to intravenous iodinated contrast usually are self-limited and require no treatment; more severe reactions are treated at the site of the scan. Pre-medication with oral steroids reduces the incidence of contrast reactions in patients with known contrast allergies.
Angiography:
Angiography is utilized to image blood vessels. Traditional angiographic techniques utilize direct injection of iodinated contrast into an artery and obtaining radiographs of the vessels of interest. Newer angiographic techniques have been developed which are non-invasive. MR Angiography utilizes special sequences to image blood vessels, and is especially helpful in analyzing brain and neck arteries. Contrast may or may not be used, depending on the circumstances. CT Angiography utilizes special reconstruction techniques following the intravenous administration of iodinated contrast. Doppler duplex ultrasound may be utilized to evaluate arteries and veins. This technique combines the standard ultrasonographic imaging of a vessel in addition to determining the blood velocity to assess both the degree of narrowing and morphologic characteristics of the vessel. No contrast is used in this technique.
Intervertebral Disk Terminology
Disk bulge:
Symmetric, circumferential extension of disk material beyond the bony margin of the interspace.
Disk protrusion:
Asymmetric extension of disk material beyond the bony margin of the interspace with a broad area of contiguity with the parent disk.
Disk extrusion:
Asymmetric extension of disk material beyond the interspace with a narrow area of contiguity with the parent disk.
Disk sequestration:
Also termed “free fragment.” Disk material within the spinal canal or neural foramen without connection to the parent disk.
Note: The term “disk herniation” is used by some physicians to include our categories of disk protrusion and/or extrusion. We preferentially use the latter terms as we find them more descriptive and clinically relevant.
Spine Terminology
Apophyseal (Facet) Joints:
Synovial-lined joints of the posterior arch of the vertebral column.
Cauda Equina:
The collection of lumbar and sacral spinal nerve roots that descend from the lower part of the spinal cord and occupy the vertebral canal below the spinal cord. The cord usually ends at the level of L1.
Diskography:
X-ray study of the spine after contrast injection into the central portion of the disk (the nucleus pulposus).
Epidural:
Situated upon or outside the dura matter.
Kyphosis:
Convexity in the curvature of the spine as viewed from the side.
Lamina:
A portion of the posterior bony arch of the vertebral column.
Laminectomy:
Surgical excision of the lamina of a vertebra.
Laminotomy:
Surgical division of the lamina of a vertebra.
Lordosis:
Concavity in the curvature of the spine as viewed from the side.
Myelography:
X-ray study of the spine after injection of contrast material into the subarachnoid space.
CT Myelography:
CT examination of the spine after injection of contrast material into the subarachnoid space.
Paramagnetic Contrast:
Contrast material for MR imaging. In post-operative lumbar spine cases, it is used intravenously to distinguish between a recurrent disk protrusion and scarring.
Scoliosis:
An appreciable lateral deviation of the normally straight vertical line of the spine as viewed from the front.
Spondylolysis:
Forward movement of the body of one of the lower lumbar vertebrae on the vertebra below it, or upon the sacrum (synonym: spondyloptosis) Interruption of the pars interarticularis of the vertebra. The cause has been debated. It is most likely an acquired abnormality due to abnormal vertebral stress sometime between infancy and early adulthood.
Spondylosis:
General term for degenerative changes of the spine.
Syringohydromyelia (Syrinx):
Central cavitation of a portion of the spinal cord. Etiologies include tumor, congenital, trauma, or idiopathic.
Tarlov Cyst:
Perineural cyst arising from the nerve root sheath.
Thecal Sac:
Located within the spinal canal and contains the spinal cord, cauda equina and CSF.
Knee Terminology
Anterior Cruciate Ligament:
Restrains anterior tibial displacement and tibial rotation.
Avascular Necrosis (AVN):
Refers to the death of bone from ischemia.
Bone Contusion/Bruise:
Microfractures of trabecular bone manifest on MRI by abnormal marrow signal.
Chondromalacia:
Thinning or absence of articular cartilage. Arthroscopic grade I (mild, not visible on MRI) through IV (severe, with associated degenerative changes in adjacent bone).
Collateral Ligaments:
The medial and lateral collateral ligaments stabilize the knee against lateral stresses.
Ganglion Cyst:
Mucin-filled cyst arising from joints, tendons, or tendon sheaths.
Intra-Articular Body:
Fragment of meniscus, bone, or cartilage in joint, which often results in locking symptoms.
Menisci:
Crescent-shaped fibrocartilaginous structures interposed between the femur and tibia which distribute vertically-directed forces across the tibial surface and protect the articular surface.
Meniscal Cyst:
Fluid collection adjacent to the meniscus associated with meniscal tears, most common laterally.
Meniscal Degeneration:
Manifest on MRI by internal signal (Grades I and II) which does not extend to an articular surface. This is often seen in asymptomatic patients.
Meniscal Signal Grades:
- Grade I – Globular internal signal, not a tear
- Grade II – Linear signal not extending to an articular surface, not a tear
- Grade III – Linear signal extending to an articular surface, a tear
Meniscal Tear:
Manifest on MRI by either meniscal abnormal linear signal extending to articular surface or by abnormal meniscal shape.
Osteochondritis Dessicans:
Devitalized bone and overlying cartilage typically involving the medical femoral condyle.
Patellar Tendon:
Extends from the inferior pole of the patella to the anterior tibial tubercle.
Popliteal (Baker’s) Cyst:
Fluid collection typically located within the posteromedial soft tissues, which communicates with the knee joint.
Posterior Cruciate Ligament:
Resists posterior tibial displacement.
Quadriceps Tendon:
Large tendon extending from the quadriceps muscles to the superior pole of the patella.
Acromioclavicular Joint:
The articulation formed by the distal clavicle and acromial process of the scapula.
Shoulder Terminology
Acromioclavicular Joint Hypertrophy:
Enlargement of one or both structures of the adjacent bone or joint capsule forming the acromioclavicular joint as a result of degenerative joint disease.
Encroachment/Impingement:
Pressure placed on a rotator cuff muscle or tendon by one or more of its surrounding structures. In some cases, this may cause pain or limited range of motion. Over a long period of time, this could cause degeneration and tear of the rotator cuff tendons.
Glenohumeral Joint:
The articulation of the humeral head with the glenoid fossa portion of the scapula.
Glenoid Labrum:
A lip of fibrous tissue, which surrounds the periphery of the glenoid fossa. This makes the shallow glenohumeral joint a deeper ball-and-socket joint.
Rotator Cuff:
The supraspinatus, infraspinatus, subscapularis and teres minor muscles and tendons which are responsible for 30-50% of upper extremity abduction as well as external and internal rotation of the humerus.
Rotator Cuff Tear:
- Full Thickness: A tear that extends from the articular surface to the bursal surface of the cuff.
- Partial Thickness: A tear involving only one surface of the cuff.
- Intrasubstance Tear: A tear wholly within the substance of a rotator cuff muscle or tendon without extension to either the bursal or articular surface.
Subacromial/Subdeltoid Bursa:
A synovial-lined potential space between the rotator cuff tendons and the acromion and deltoid muscle.
Tendinosis:
Degenerative changes within a tendon structure indicating a chronic, long-term process.
EMG Terminology
Electrodiagnostic Testing – EMG and NCV:
These tests are best performed by a physician with formal training in these procedures, usually a neurologist or physiatrist. They are outpatient office or clinic procedures and do not require hospitalization or fasting. A procedure’s length may average anywhere from ten minutes to sixty minutes, depending on the cooperation of the patient and the number of areas requiring testing. Electrodiagnostic testing is conducted while the patient is lying on an examination table. It consists of two parts. The first part is called a Nerve Conduction Velocity (NCV), which involves gentle and brief electrical impulses delivered through a probe to the nerves in the arm or leg. This test determines how fast or slow these nerves are conducting the current. The speed of the traveling impulse indicates what state of health or disease the tested nerve is in.
The second part of the test is called Electromyography (EMG) which also involves a needle examination. The needle is actually not a regular blood drawing needle but smaller. It does not draw the patient’s blood or inject medication; it is tiny and solid, very similar to a Chinese acupuncture needle. The needle is inserted through the skin, into the patient’s arm or leg muscle and does not damage any organ or nerves. The test is used to evaluate muscle weakness. It can help to differentiate primary muscle conditions from muscle weakness caused by nerve abnormalities. It can also differentiate between true weakness and reduced use due to pain or lack of motivation.
EMG Terminology:
Electrodiagnostic test:
Term that some physicians use to include NCV, NCS and/or EMG.
EMG:
Abbreviation for Electromyography. A procedure which utilizes a needle electrode to evaluate muscle weakness.
NCV/NCS:
Abbreviation for Nerve Conduction Velocity/Study, a nerve test which utilizes mild and gentle electrical stimulation to the nerve to determine the medical condition of that nerve.
Fibrillation:
Action potentials from degenerated muscle fibers. In other terms, an abnormality detected and recorded by the EMG machine indicating injury to a particular nerve and muscle group.
Tinel’s Sign:
Tingling or electric shock-like sensation extending into the fingers supplied by the median nerve elicited by tapping over the volar aspect of the wrist. A positive Tinel’s sign is indicative of carpal tunnel syndrome.
Pathology:
Carpal Tunnel Syndrome:
Sometimes abbreviated CTS. This condition is due to median nerve entrapment under the transverse carpal ligament (flexor retinaculum) of the wrist. Predisposing conditions may include repetitive hand activity, arthritis, diabetes, hypothyroidism, wrist fracture or dislocation, pregnancy, carpal tunnel masses or inherited conditions. Clinical symptoms include arm pain as well as numbness of the first three and one-half digits, which may be aggravated by sleep, driving, or sewing.
Cubital Tunnel Syndrome:
This occurs when the ulnar nerve is entrapped (compressed) at the elbow within the cubital tunnel: the epicondylar groove located behind the “funny bone.” Clinical symptoms include hand pain or weakness, as well as numbness in the fourth and fifth digits provoked by prolonged elbow flexion.
Guyon’s Canal Syndrome:
Entrapment of the ulnar nerve at the wrist. Symptoms are very similar to those of cubital tunnel syndrome. Differentiation can be made through Electrodiagnostic testing.
Peripheral Neuropathy:
Dysfunction of the peripheral nerves, which can be seen in patients with diabetes, alcoholism, uremia, nutritional deficiencies, or toxic exposure. Symptoms are numbness, tingling or burning sensations of distal limbs symmetrically. Electrodiagnostic testing can be helpful in distinguishing peripheral neuropathy from other nerve disorders.
Radiculopathy:
Compression of the nerve root at the neck or back level as it exits the spine with symptoms of pain and/or numbness radiating to the arm or leg. The location of the radiating pain can pinpoint the exact nerve involved (see dermatome chart located in the Spine section). Common causes are extruded disks and degenerative disease of the spine.
Sciatica:
Pain radiating down the leg (radiculopathy) in the course of the sciatic nerve and its branches usually resulting from lumbar spine pathology such as disk extrusion or degenerative diseas of the spine.
Tarsal Tunnel Syndrome:
Entrapment of the tibial nerve at the medial ankle which may be the result of conditions such as diabetes, inherited abnormalities, trauma or mass. This condition is very similar in mechanism to carpal tunnel syndrome. Symptoms include pain, burning, numbness, or tingling at the ankle, heel, and sole of the foot.
Foot & Ankle Terminology
Anatomy:
There are 26 bones in the foot (not including sesamoids and/or accessory bones):
- Hindfoot: Talus and calcaneus (2)
- Midfoot: Navicular, cuboid, medial cuneiform, middle cuneiform, lateral cuneiform (5)
- Forefoot: Metatarsals (5) and phalanges (14)
Achilles Tendon:
The tendon of the gastrocnemius and soleus muscles of the leg, attaches to the heel and plantar flexes the ankle. Common pathology includes rupture and chronic tendinitis.
Anterior Talofibular Ligament:
The anterior-most and weakest of the lateral supporting ligaments. It is the first ligament to tear in severe inversion injuries.
Deltoid Ligament:
Complex band of ligaments, which attach the medial tibia to the hindfoot.
Fibula:
This is one of the longest and thinnest bones of the body. It is the outer and smaller bone of the leg from the ankle to the knee, articulating above with the tibia and below with the tibia and talus.
Flexor Hallucis Longus Tendon:
The tendon of the flexor hallucis longus muscle. Located in the posteromedial soft tissues of the ankle. A flexor tendon of the first toe which inverts and flexes the foot and is a common site of tenosynovitis.
Peroneus Longus and Brevis Tendons:
The everting tendons of the ankle, which run side-by-side behind the fibula, these may rupture in lateral ankle trauma.
Sural Nerve:
Located in the lateral soft tissues, posterior to the peroneus tendons. Injured in fractures of the fifth metatarsal or from compression (ganglions, tight ski boots), producing pain or numbness.
Tibia:
Also known as the “shinbone,” this is the inner and larger bone of the leg between the knee and ankle articulating with the femur and fibula above and with the talus and fibula below.
Tibialis Posterior Tendon:
A large flexor tendon, which runs along the posteromedial aspect of the ankle, prone to chronic and acute rupture. When torn, it presents as a flat foot deformity.
Pathology:
Accessory Soleus:
Congenital abnormality. It is an “extra” muscle that can present as a painful mass following exercise.
Morton’s Neuroma:
Focal fibrous enlargement of the nerve between the metatarsal heads (usually the 3rd and 4th). Appears as a mass on MRI. Sometimes contrast-enhanced MRI may be needed to detect these small masses.
Osteochondral Lesion of The Talus:
A talar dome fracture that extends to the joint space. This may lead to a displaced bone fragment within the joint (loose body).
Stress Fractures:
Fatigue Fractures:
Fracture in normal bone due to repetitive stress, often not visible on x-ray.
Insufficiency Fractures:
Stress fracture in abnormal, weak bone.
Tendon Tears:
- Type I: Partially torn, bulbous, enlarged tendon with vertical splits and/or defects.
- Type II: Partially torn, thin tendon.
- Type III: Complete tendon rupture with a gap.
Tendinitis:
Intrinsic or intrasubstance inflammation of the tendon.
Tenosynovitis:
Inflammation of the synovial lining (membrane), which surrounds most tendons. It is seen as fluid surrounding a tendon on MRI.
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