Computed tomography (CT)

$$$

Evaluation of acute craniofacial trauma, acute neurologic dysfunction (<72 hours) from suspected intracranial or subarachnoid hemorrhage.

Further characterization of intracranial masses identified by MRI (presence or absence of calcium or involvement of the bony calvarium).

Evaluation of sinus disease and temporal bone disease.

Rapid acquisition makes it the modality of choice for trauma.

Superb spatial resolution.

Superior to MRI in detection of hemorrhage within the first 24–48 hours.

Artifacts from bone may interfere with detection of disease at the skull base and in the posterior fossa. Generally limited to transaxial views. Direct coronal images of paranasal sinuses and temporal bones are routinely obtained if patient can lie prone.

Contraindications and risks: Caution in pregnancy because of the potential harm of ionizing radiation to the fetus. See Risks of CT and Angiographic Intravenous Contrast Agents.

Normal hydration.

Sedation of agitated patients.

Recent serum creatinine determination if intravenous contrast is to be used.

CT angiography (CTA)

$$$

Evaluation of cerebral arteriovenous malformations, intracranial aneurysm.

Rapid acquisition makes it an excellent choice for evaluation of blood vessels in stroke.

Can cover a large territory, including down to the heart.

Superb spatial resolution.

Artifacts from bone may interfere with detection of disease at the skull base and in the posterior fossa. Generally limited to transaxial views. Direct coronal images of paranasal sinuses and temporal bones are routinely obtained if patient can lie prone.

Contraindications and risks: Caution in pregnancy because of the potential harm of ionizing radiation to the fetus. See Risks of CT and Angiographic Intravenous Contrast Agents.

Normal hydration.

Sedation of agitated patients.

Recent serum creatinine determination if intravenous contrast is to be used.

Magnetic resonance imaging (MRI)

Evaluation of essentially all intracranial disease except those listed above for CT.

Provides excellent tissue contrast resolution, multiplanar capability.

Can detect flowing blood and cryptic vascular malformations.

Can detect demyelinating and dysmyelinating disease.

No ionizing radiation.

Subject to motion artifacts.

Inferior to CT in the setting of acute trauma because it is insensitive to acute hemorrhage, incompatible with traction devices, inferior in detection of bony injury and foreign bodies, and requires longer image acquisition time.

Special instrumentation required for patients on life support.

Contraindications and risks: Contraindicated in patients with cardiac pacemakers, intraocular metallic foreign bodies, intracranial aneurysm clips, cochlear implants, and some artificial heart valves.

Sedation of agitated patients.

Screening CT or plain radiograph images of orbits if history suggests possible metallic foreign body in the eye.

Magnetic resonance angiography/venography (MRA/MRV)

Evaluation of cerebral arteriovenous malformations, intracranial aneurysm, and blood supply of vascular tumors as aid to operative planning (MRA).

Evaluation of dural sinus thrombosis (MRV).

No ionizing radiation.

No iodinated contrast needed.

Subject to motion artifacts.

Special instrumentation required for patients on life support.

Contraindications and risks: Contraindicated in patients with cardiac pacemakers, intraocular metallic foreign bodies, intracranial aneurysm clips, cochlear implants, and some artificial heart valves.

Sedation of agitated patients.

Screening CT or plain radiograph images of orbits if history suggests possible metallic foreign body in the eye.

Brain scan (radionuclide)

$$

Confirmation of brain death.

Confirmation of brain death not impeded by hypothermia or barbiturate coma.

Can be portable.

Limited resolution.

Delayed imaging required with some agents.

Cannot be used alone to establish diagnosis of brain death. Must be used in combination with clinical examination or cerebral angiography to establish diagnosis.

Contraindications and risks: Caution in pregnancy because of the potential harm of ionizing radiation to the fetus.

Premedicate with potassium perchlorate when using TcO4 to block choroid plexus uptake.

Positron emission tomography (PET)/Single Photon Emission Computed Tomography (SPECT) brain scan

$$$

Evaluation of suspected dementia.

Evaluation of medically refractory seizures.

Provides functional information.

Can localize seizure focus prior to surgical excision.

Up to 82% positive predictive value for Alzheimer’s dementia in appropriate clinical settings.

Provides cross-sectional images and therefore improved lesion localization compared with planar imaging techniques.

Limited resolution compared with MRI and CT.

Limited application in work-up of dementia due to low specificity of images and fact that test results do not alter clinical management.

Contraindications and risks: Caution in pregnancy because of potential harm of ionizing radiation to the fetus.

Sedation of agitated patients

Cisternography (radionuclide)

$$

Evaluation of hydrocephalus (particularly normal pressure), CSF rhinorrhea or otorrhea, and ventricular shunt patency.

Provides functional information.

Can help distinguish normal pressure hydrocephalus from senile atrophy.

Can detect CSF leaks.

Requires multiple delayed imaging sessions up to 48–72 hours after injection.

Contraindications and risks: Caution in pregnancy because of the potential harm of ionizing radiation to the fetus.

Sedation of agitated patients.

For suspected CSF leak, pack the patient’s nose or ears with cotton pledgets before administration of dose.

Must follow strict sterile precautions for intrathecal injection.

Magnetic resonance imaging (MRI)

Evaluation of upper aerodigestive tract.

Staging of neck masses.

Differentiation of lymphadenopathy from blood vessels.

Evaluation of head and neck malignancy, thyroid nodules, parathyroid adenoma, lymphadenopathy, retropharyngeal abscess, brachial plexopathy.

Provides excellent tissue contrast resolution.

Tissue differentiation of malignancy or abscess from benign tumor often possible.

Sagittal and coronal planar imaging possible. Multiplanar capability especially advantageous regarding brachial plexus.

No iodinated contrast needed to distinguish lymphadenopathy from blood vessels.

Subject to motion artifacts, particularly those of carotid pulsation and swallowing.

Special instrumentation required for patients on life support.

Contraindications and risks: Contraindicated in patients with cardiac pacemakers, intraocular metallic foreign bodies, intracranial aneurysm clips, cochlear implants, and some artificial heart valves.

Sedation of agitated patients.

Screening CT or plain radiograph images of orbits if history suggests possible metallic foreign body in the eye.

Magnetic resonance angiography (MRA)

Evaluation of carotid bifurcation atherosclerosis, cervicocranial arterial dissection.

No ionizing radiation.

No iodinated contrast needed.

MRA of the carotid arteries can be a sufficient preoperative evaluation regarding critical stenosis when local expertise exists.

Subject to motion artifacts, particularly from carotid pulsation and swallowing.

Special instrumentation required for patients on life support.

Contraindications and risks: Contraindicated in patients with cardiac pacemakers, intraocular metallic foreign bodies, intra-cranial aneurysm clips, cochlear implants, and some artificial heart valves.

Sedation of agitated patients.

Screening CT or plain radiograph images of orbits if history suggests possible metallic foreign body in the eye.

Computed tomography (CT)

$$$

Evaluation of the upper aerodigestive tract.

Staging of neck masses for patients who are not candidates for MRI.

Evaluation of suspected abscess.

Rapid.

Superb spatial resolution.

Can guide percutaneous fine-needle aspiration of possible tumor or abscess.

Adequate intravenous contrast enhancement of vascular structures is mandatory for accurate interpretation.

Contraindications and risks: See Risks of CT and Angiographic Intravenous Contrast Agents.

Normal hydration.

Sedation of agitated patients.

Recent serum creatinine determination.

Ultrasound (US)

$$

Patency and morphology of arteries and veins.

Evaluation of thyroid and parathyroid.

Guidance for percutaneous fine-needle aspiration biopsy of neck lesions.

Can detect and monitor atherosclerotic stenosis of carotid arteries noninvasively and without iodinated contrast.

Technically demanding, operator-dependent.

Patient must lie supine and still for 1 hour.

None.

Ultrasound (US)

$$

Determination whether a palpable nodule is a cyst or solid mass and whether multiple nodules are present.

Assessment of response to suppressive therapy.

Screening patients with a history of radiation to the head and neck. Guidance for biopsy.

Noninvasive.

No ionizing radiation.

Can be portable.

Can image in all planes.

Cannot distinguish between benign and malignant lesions unless local invasion is demonstrated.

Technique very operator-dependent.

Contraindications and risks: None.

Thyroid uptake and scan (radionuclide)

$$

Uptake indicated for evaluation of clinical hypothyroidism, hyperthyroidism, thyroiditis, effects of thyroid-stimulating and thyroid-suppressing medications, and for calculation of therapeutic radiation dosage.

Scanning indicated for above as well as evaluation of palpable nodules, mediastinal mass, and screening of patients with history of head and neck irradiation for thyroid cancer. Total body scanning used for postoperative evaluation of thyroid cancer metastases.

Demonstrates both morphology and function.

Can identify ectopic thyroid tissue and “cold” nodules that have a greater risk of malignancy.

Imaging of whole body with one dose (131I).

Substances interfering with test include iodides in vitamins and medicines, antithyroid drugs, corticosteroids, and intravascular contrast agents.

Delayed imaging is required with iodides (123 I, 6 hours and 24 hours; 131 I total body, 72 hours).

Test may not visualize thyroid gland in subacute thyroiditis.

Contraindications and risks: Not advised in pregnancy because of the risk of ionizing radiation to the fetus (iodides cross placenta and concentrate in fetal thyroid). Significant radiation exposure occurs in total body scanning with 131 I; patients should be instructed about precautionary measures by nuclear medicine personnel.

Administration of dose after a 4- to 6-hour fast aids absorption.

Discontinue all interfering substances prior to test, especially thyroid-suppressing medications: T3 (1 week), T4 (4–6 weeks), propylthiouracil (2 weeks).

Thyroid therapy (radionuclide)

$$$

Hyperthyroidism and some thyroid carcinomas (papillary and follicular types are amenable to treatment, whereas medullary and anaplastic types are not).

Noninvasive alternative to surgery.

Rarely, radiation thyroiditis may occur 1–3 days after therapy.

Hypothyroidism occurs commonly as a long-term complication.

Higher doses that are required to treat thyroid carcinoma may result in pulmonary fibrosis.

Contraindications and risks: Contraindicated in pregnancy and lactation. Contraindicated in patients with metastatic thyroid cancer to the brain, because treatment may result in brain edema and subsequent herniation, and in those <20 years of age with hyperthyroidism because of possible increased risk of thyroid cancer later in life. After treatment, a patient’s activities are restricted to limit total exposure of any member of the general public until radiation level is ≤ 0.5 rem.

After treatment, patients must isolate all bodily secretions from household members.

High doses for treatment of thyroid carcinoma may necessitate hospitalization.

Parathyroid scan (radionuclide)

$$

Evaluation of suspected parathyroid adenoma.

Identifies hyperfunctioning tissue, which is useful when planning surgery.

Small adenomas (<500 mg) may not be detected.

Contraindications and risks: Caution in pregnancy is advised because of the risk of ionizing radiation to the fetus.

Requires strict patient immobility during scanning.

Chest radiograph

$

Evaluation of pleural and parenchymal pulmonary disease, mediastinal disease, cardiogenic and noncardiogenic pulmonary edema, congenital and acquired cardiac disease.

Screening for traumatic aortic rupture (though CT is playing an increasing role).

Evaluation of possible pneumothorax (expiratory upright film) or pleural effusion.

Inexpensive.

Widely available.

Difficult to distinguish between causes of hilar and mediastinal enlargement (ie, vasculature versus adenopathy).

Not sensitive for small pulmonary nodules.

Contraindications and risks: Caution in pregnancy because of the potential harm of ionizing radiation to the fetus.

None.

Computed tomography (CT)

$$$

Evaluation of thoracic trauma.

Evaluation of mediastinal and hilar tumor.

Evaluation and staging of primary and metastatic lung neoplasm.

Characterization of pulmonary nodules.

Differentiation of parenchymal versus pleural process (ie, lung abscess versus empyema).

Evaluation of interstitial lung disease (1-mm thin sections), aortic dissection, and aneurysm.

Screening for lung cancer in high-risk populations.

Rapid.

Superb spatial resolution.

Can guide percutaneous fine-needle aspiration of possible tumor or abscess.

Patient cooperation required for appropriate breath-holding.

Contraindications and risks: Caution in pregnancy because of the potential harm of ionizing radiation to the fetus. See Risks of CT and Angiographic Intravenous Contrast Agents.

Preferably NPO for 2 hours before study.

Normal hydration.

Sedation of agitated patients.

Recent serum creatinine determination.

Magnetic resonance imaging (MRI)

Evaluation of mediastinal masses.

Discrimination between hilar vessels and enlarged lymph nodes.

Tumor staging (especially when invasion of vessels or pericardium is suspected).

Evaluation of aortic dissection, aortic aneurysm, congenital and acquired cardiac disease.

Provides excellent tissue contrast resolution and multiplanar capability.

No ionizing radiation.

Subject to motion artifacts.

Contraindications and risks: Contraindicated in patients with cardiac pacemakers, intraocular metallic foreign bodies, intracranial aneurysm clips, cochlear implants, and some artificial heart valves.

Sedation of agitated patients.

Screening CT of the orbits if history suggests possible metallic foreign body in the eye.

Positron emission tomography/Computed tomography (PET/CT)

Evaluation for mediastinal masses and metastases.

Discrimination between benign and malignant lymph nodes.

Tumor staging and treatment monitoring.

Combines metabolic and anatomic information.

Large area of coverage (can image whole body)

Patient cooperation required for appropriate breath-holding.

Contraindications and risks: Contraindicated in pregnancy because of the potential harm of ionizing radiation to the fetus. See Risks of CT and Angiographic Intravenous Contrast Agents.

Preferably NPO for 2 hours before study.

Normal hydration.

Sedation of agitated patients.

Recent serum creatinine determination.

Ventilation-perfusion scan (radionuclide)

V̇ = $$

Q̇ = $$

V̇ + Q̇ = $−$$

Evaluation of pulmonary embolism or burn inhalation injury.

Preoperative evaluation of patients with chronic obstructive pulmonary disease and of those who are candidates for pneumonectomy.

Noninvasive.

Provides functional information in preoperative assessment.

Permits determination of differential and regional lung function in preoperative assessment.

Documented pulmonary embolism is extremely rare with normal perfusion scan.

Patients must be able to cooperate for ventilation portion of the examination.

There is a high proportion of intermediate probability studies in patients with underlying lung disease. The likelihood of pulmonary embolism ranges from 20%–80% in these cases.

A patient who has a low probability scan still has a chance ranging from nil to 19% of having a pulmonary embolus.

Contraindications and risks: Patients with severe pulmonary artery hypertension or significant right-to-left shunts should have fewer particles injected. Caution advised in pregnancy because of risk of ionizing radiation to the fetus.

Current chest radiograph is mandatory for interpretation.

Computed tomography (CT)

$$$

Evaluation of clinically suspected pulmonary embolism.

Rapid.

High sensitivity and specificity for clinically relevant pulmonary emboli.

Allows determination of causes other than pulmonary embolism for dyspnea.

Evaluation of pulmonary vein anatomy before electrophysiology ablation.

Respiratory motion artifacts can be a problem in dyspneic patients and older CT scanners. High-quality study requires breath-holding of approximately 10–20 seconds.

Specific imaging protocol utilized which limits diagnostic information for other abnormalities.

Contraindications and risks: Caution in pregnancy because of potential harm of ionizing radiation to fetus. See Risks of CT and Angiographic Intravenous Contrast Agents.

Large-gauge intravenous access (minimum 20-gauge) required.

Prebreathing oxygen may help dyspneic patients perform adequate breath hold.

Normal hydration.

Preferably NPO for 2 hours before study.

Recent serum creatinine determination.