Diagnostics for Patients with Neurological Disorders
Joanne V. Hickey
Diagnostic procedures and laboratory tests for patients with suspected or present neurological disorders continue to develop and become more sophisticated. Along with sophisticated and complex diagnostic technologies is a growing cadre of highly specialized health care professionals skilled in the techniques of testing and the interpretation of the findings that influence diagnostic and treatment decisions. The ongoing expansion of computed tomography (CT) and magnetic resonance imaging (MRI) technologies has relegated some highly utilized diagnostics such as cerebral angiography to a narrowed scope of fewer diagnostic work-ups while noninvasive CT angiography (CTA) and magnetic resonance angiography (MRA) replace the traditional invasive angiography. The new knowledge of genetics and genomics is emerging as important in the recognition of subtypes of neurological diseases such as familial Parkinson’s disease and familial cerebral aneurysms. The rapid development of genetic testing will influence how patients will be diagnosed and treated in future.
More and more diagnostic procedures are scheduled as outpatient procedures in special hospital areas (e.g., radiology departments, special procedures departments) or in central diagnostic facilities that report results to referring physicians. Outpatient procedures are driven by cost-containment demands, proven safety of outpatient diagnostic procedures, and patient convenience. On the day of the diagnostic procedure, the patient reports to a special hospital area (e.g., 23-hour unit, ambulatory center) or other facility, undergoes the procedure, recovers in a special unit, and is discharged, usually without an overnight stay. In other instances, diagnostics are ordered during hospitalization.
The variations of entry points for diagnostic procedures create special challenges for patient-centered care including preparation and education of the patient. Patient education, a key responsibility of the nurse, has been changed. The large number of people undergoing diagnostic procedures with short hospital stays or on an outpatient ambulatory basis presents special challenges for education and preparation. The nurse may not see the patient until arrival for the test, or there may not be a nurse present at all. Education may be provided through a direct patient-nurse conference, a telephone call, mailed printed material (e.g., instructions and booklets), videotape or audiocassette, e-mail, or referral to a website. Regardless of educational media used, there is always a need for follow-up to answer questions and clarify information.
PATIENT AND FAMILY TEACHING
Focus of Patient Teaching
Patients undergoing a diagnostic procedure need a general explanation of the procedure with special emphasis on what to anticipate and their role as participants. For example, patients who are about to undergo a brain CT scan should be told that they must remain very still while the scan is being taken to ensure accuracy and high-quality graphics. Adapt the explanation to the patient’s level of understanding and desire for information. If a patient’s level of consciousness (LOC) is altered sufficiently to affect attention, comprehension, understanding, memory, and appreciation of causal associations, provide a simple explanation. Repetition and reinforcement of information may be necessary because of cognitive deficits (e.g., memory), anxiety, or fear. Include information about where the procedure will be conducted, who will be there, and where the patient will be taken upon completion of the procedure.
Written consent is required for many diagnostic procedures although there may be some variation among institutions. Adhere to institutional policies and procedure manuals. Part of patient education is providing information so that the patient can make informed decisions. If a patient has an altered LOC, cognitive deficits, or other impairments that will affect ability to give informed consent, a family member must provide written consent and it must be witnessed. It is usually the physician’s responsibility to obtain written consent after explaining the procedure and the risks and answering questions. The nurse may be asked to witness the consent.
OUTPATIENT PROCEDURES
For outpatient procedures, nurses must be knowledgeable about procedures and related protocols and also be sensitive to the anxiety or fear related to the diagnostic process. Patients and families are often aware that the purpose of the procedure is to rule in or rule out serious diagnoses. As a result, they are often anxious and fearful and need emotional support and education.
HOSPITALIZED PATIENTS AND PROCEDURES
For hospitalized patients, the care nurse assumes responsibility for ensuring that the appropriate patient education has been provided. Portions of education may be delegated to other personnel, but the nurse is accountable for satisfactory completion of all aspects of education. Depending on the stability of the patient, unit personnel may accompany the patient to the diagnostic procedure. Sometimes it is an absolute necessity for a registered nurse to accompany the patient, such as when frequent suctioning is required or the patient is hemodynamically unstable or needs frequent monitoring. Follow a transport protocol, such as one published by the Society of Critical Care Medicine,1 to ensure patient safety. For the patient with impaired cognitive function or with a high anxiety level, presence of the nurse may make the difference between success and failure of the diagnostic procedure. It is often necessary for the patient to cooperate, lie quietly, or follow instructions. The familiar nurse is often able to gain the patient’s cooperation. Judicious use of sedation before and during the procedure is also useful and sometimes necessary.
At other times, the unit care nurse completes components of preprocedural preparation in the clinical unit. Auxiliary personnel who are solely responsible for patient transport then take the patient to the designated area. After the patient has arrived at the procedure site, technicians and/or the physician are the principal personnel involved. Therefore, it is most important that a proper explanation of the procedure and what to expect be provided to the patient beforehand.
X-RAYS OF THE HEAD AND VERTEBRAL COLUMN
Skull/Facial X-Rays
Skull films are ordered infrequently because CT scans and MRI provide much more detailed anatomic information than is available from skull films. If a CT scan is ordered, the need for skull films is eliminated. One of the most frequent reasons for ordering skull films is to determine whether a skull fracture is present. When skull films are ordered, they usually include anteroposterior (AP) and lateral (LA) radiographic views (Fig. 6-1). Other angles may be included in the series to provide information about specific areas such as the orbits or paranasal sinuses. Films provide information about the presence of a skull or facial fracture, unusual calcification or presence of air, the size and shape of skull or facial bone, and bone erosion, particularly of the sella turcica. Skull films are reviewed in an orderly fashion beginning with identification of certain landmarks. For example, the pineal body, normally calcified in the adult, is a midline structure. If it is skewed to one side, it suggests that pressure from a space-occupying lesion is responsible for the midline deviation. Abnormal calcification areas raise suspicion of a calcified component located within a tumor; bone erosion suggests the presence of an intracranial lesion close to bone. Fractures through the base of the
skull or paranasal sinuses may produce pneumocephalus or air pockets in the cranial vault or brain.
skull or paranasal sinuses may produce pneumocephalus or air pockets in the cranial vault or brain.
 Figure 6-1 ▪ X-ray of skull. (Courtesy GE Healthcare.) |
Patient Preparation and Postprocedural Care
Other than encouraging the patient to lie still for the few moments necessary to take the films, no preparation or postprocedural care is required.
SPINAL X-RAYS
Spinal films are simple radiographs of various regions of the spine: cervical (Fig. 6-2), thoracic, lumbar, or sacral. The most commonly obtained views are the AP and the LA. Because the vertebrae are highly irregular anatomic structures, it is easy to overlook a fracture. This is why both AP and LA films are necessary to rule out a fracture. Indications for spinal films include trauma to the back or vertebral column or back pain with motor or sensory impairment.
In the emergency department, AP and LA films of the cervical region are ordered to rule out cervical fracture. To view the seventh cervical vertebrae, it is often necessary to pull the shoulders downward, especially in muscular men. Viewing of the odontoid process to determine a fracture or instability of C-1 and C-2 vertebrae may require an open-mouth view. Flexion-extension films are used to evaluate the presence of spinal injury. When ordered, the patient must be cooperative and cognitively intact to be able to report pain or onset of neurological symptoms. These films are taken under the direct supervision of the physician. An MRI or CT scan may replace or follow a spinal x-ray for more detailed information.
Abnormalities found on spinal films may include wedging or compression of a vertebra, bone decalcification (osteoporosis), irregular bone calcification (osteophyte/spur), narrowing of the vertebral canal, vertebral fractures and/or dislocations, and spondylosis.
 Figure 6-2 ▪ X-ray of cervical spine. (Courtesy GE Healthcare.) |
Patient Preparation and Postprocedural Care
There is no preparation or postprocedural care required other than to encourage the patient to lie still for the few moments necessary to take the films.
ANATOMIC IMAGING TECHNIQUES OF THE BRAIN
The CT scan and MRI are the anatomic imaging cornerstones of the diagnostic work-up for neurological and neurosurgical patients and are readily available technologies (Table 6-1). These technologies have made many previously ordered procedures such as skull and spinal films obsolete.
Computed Tomography
CT, first introduced in 1972 by Hounsfield,2 is based on the use of conventional ionized radiation that is attenuated as it passes through the skull, cerebrospinal fluid (CSF), cerebral gray and white matter, and blood vessels. More than thirty thousand 2- to 4-mm x-ray beams are directed successively at several horizontal levels in any plane.3 Detectors measure the degree of attenuation of the exiting radiation. Computers integrate this information and construct the images as cross-section images. The thickness of a cross-section, which is called a cut or slice, can vary from 1.5 to 10 mm although most cuts are no more than 5 mm to allow for greater
precision in identifying small abnormal areas. Each cut is subdivided into a grid of tiny cubes or volume elements called voxels. The degree of attenuation within each voxel is measured as a numeric value of tissue density and is converted to gray scale values with lower numbers coded as black (i.e., air, CSF) and higher numbers coded as white (i.e., bone). The differing densities of bone, CSF, blood, and gray and white matter are distinguishable in the resulting picture. Films of the various cuts are then arranged sequentially for review.
precision in identifying small abnormal areas. Each cut is subdivided into a grid of tiny cubes or volume elements called voxels. The degree of attenuation within each voxel is measured as a numeric value of tissue density and is converted to gray scale values with lower numbers coded as black (i.e., air, CSF) and higher numbers coded as white (i.e., bone). The differing densities of bone, CSF, blood, and gray and white matter are distinguishable in the resulting picture. Films of the various cuts are then arranged sequentially for review.
TABLE 6-1 COMPARISON OF INDICATIONS FOR COMPUTED TOMOGRAPHY (CT) AND MAGNETIC RESONANCE IMAGING (MRI) | ||||||||||||||||||||
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Clinical Applications
The American College of Radiology and American Society of Neuroradiology4 have published guidelines for use of CTs in clinical practice. The more recent generation of CT scanners provide extraordinary clarity of the brain, orbits, and spine. Detailed visualization of sulci, caudate and lenticular nuclei, the internal capsule, thalami, optic nerves, the brainstem, the cerebellum, and the spinal cord is provided. One can visualize hemorrhage, cerebral edema, abscess, and tumor as well as the precise size and position of the ventricles and midline structures. A CT can be ordered with or without contrast. A CT without contrast is ordered to rule out bleeding or a hematoma when a cerebral aneurysm is suspected, and to screen for hemorrhage in candidates for thrombolytic therapy with a diagnosis of ischemic stroke. A CT with contrast is ordered when more precise detail is desired. Serial CT scans can be used to follow the resolution of cerebral hemorrhage or edema (Fig. 6-3).
Recent advances in CT technology of spiral and helical CT scans have greatly increased the speed of the scanning procedure and have made possible the visualization of cerebral vasculature (i.e., CTA).3 The newest addition to CT technology is a portable CT scanner. The portability of this equipment allows the scanner to be brought to the emergency room or patient’s bedside (e.g., intensive care unit [ICU]; other units) for scanning and immediate availability of quality images for review. NeuroLogica Corporation (Danvers, MA) offers light weight, high speed, and portable scanners called CereTom. The portable scanner is especially useful in the ICU environment in that the patient does not need to be disconnected from monitoring devices such as the intracranial pressure (ICP) monitor or ventilator.5 Transporting a patient from the ICU to a radiology site for scanning has always placed the patient at high risk for unexpected events such as desaturation, hypotension, hemodynamic instability, dislodgement of endotracheal tube or other lines, aspiration, and cardiac arrest. Avoiding such transport eliminates the risk to the patient’s safety.6, 7
 Figure 6-3 ▪ Abnormal computed tomography of brain. (Courtesy GE Healthcare.) |
A version of the portable scanner is also available for intraoperative applications to assist the neurosurgeon in stunt placement, astrocytoma reduction, arteriovenous malformation resection, hematoma evacuation, and other procedures requiring checking for precision.
Procedure
The procedure and equipment are briefly explained to the patient, and reassurance is given that the procedure is painless. No motion will be felt, and a clicking sound from the equipment is to be expected. Even though the technician and radiologist are outside the room, they can see and maintain voice contact with the patient through an intercom system at all times. The patient lies on a movable radiographic table with his or her head carefully positioned and immobilized. The head of the table is inserted into the scanner (Fig. 6-4). A movable circular frame revolves around the head, making clicking sounds while taking numerous scans at different angles.
CT scans are done with or without contrast media. Use of an iodinated radiopaque medium enhances image sharpness and further augments areas of pathology that resulted from breakdown of the blood-brain barrier. If used, contrast medium is administered intravenously. Before administering, consider contraindications which include allergic reaction to shellfish or iodinated dye. CT scanning can begin 10 seconds after the contrast infusion begins.
When contrast medium is used, a capital “C” will be noted somewhere on the films. The entire CT scanning procedure takes about 10 minutes. Newer-generation scanners have cut the time of scanning.
When contrast medium is used, a capital “C” will be noted somewhere on the films. The entire CT scanning procedure takes about 10 minutes. Newer-generation scanners have cut the time of scanning.
 Figure 6-4 ▪ Normal computed tomography technology. (Courtesy GE Healthcare.) |
Advantages and Disadvantages
The advantages of CT scans are many. It is a painless, low-cost, widely available diagnostic tool that requires only minutes to complete, and can be performed on both conscious and unconscious patients. It is useful in rapidly developing neurological conditions when monitoring and life-support equipment is necessary. CT is sensitive to detect acute hemorrhage and calcifications and demonstrates the anatomy of skull and vertebral bones well. CT has drastically reduced the need for more dangerous and expensive diagnostic tests. It is also useful when MRI is contraindicated because of metal aneurysm clips, orthopedic prostheses, foreign objects in the eye, pacemakers, and other metal implants. Finally, the cost of a CT scan varies with the type and complexity of the study; generally it is about half the cost of an MRI.8
Some disadvantages are also noted. CT scans include ionizing radiation exposure about equal to that of skull films. By comparison, an MRI does not use radiation. CT scans have decreased sensitivity for detection of many common neurological diseases, lesions adjacent to bone, small soft tissue lesions, posterior fossa (cerebellum and brainstem) lesions, and floor of the middle fossa lesions.3 Claustrophobia is a contraindication for a CT scan. A patient who is unable to tolerate his or her head being in the confined space of a CT scanner is not a candidate for a CT scan.
Patient Preparation and Postprocedural Care
Screen for claustrophobia. All jewelry, eyeglasses, and hair clips or pins are removed from the head and neck. Unless a contrast medium will be administered, there are no dietary restrictions or other screening requirements before the procedure. The need to remain perfectly still is emphasized because movement can cause artifacts that will affect the clarity of the pictures. Agitated or uncooperative patients will require short-acting intravenous (IV) sedation such as lorazepam (Ativan) to ensure the necessary quality of the pictures.
Before the contrast medium is administered, a skin test may be done to check for an allergic reaction in high-risk patients. The blood urea nitrogen and creatinine levels are checked within 48 hours of the procedure to assess adequate kidney function. Most protocols require the patient to have had nothing by mouth for 4 to 8 hours before the test. Some patients experience flushing or a feeling of warmth, transient headache, a salty taste in the mouth, nausea, or vomiting when the contrast medium is administered; patients should be prepared for these possible reactions.
After the procedure, patients who have received contrast medium should be observed for signs and symptoms of delayed allergic reactions such as hives, skin rash, itching, nausea, headache, or seizures. If symptoms are severe, antihistamines may be ordered. IV hydration or oral fluid intake for hydration to facilitate clearance of contrast medium is very important. Tubular necrosis and acute kidney failure can result from inadequate hydration; older patients are at higher risk because of age-related kidney function changes. Monitor for both adequate intake and output.
Other Uses of Computed Tomography Technology in Diagnostics
CTA is emerging as an alternative to MRA for imaging extracranial and intracranial blood vessels. The CTA has several advantages over the MRA. It is faster (<32 seconds) than MRA and can be used with intubated patients or those with aneurysmal clips. It offers multiplanar views of the cerebral vasculature and visualization of slow flow or turbulent flow in aneurysms. Finally, it identifies plaque location and characteristics.9 The limitations include risks associated with iodinated contrast media use and some difficulty in imaging the posterior inferior cerebellar arteries.10
Xenon-enhanced computed tomography (XeCT) evaluates cerebral blood flow (CBF). A mixture of oxygen and xenon is inhaled and the xenon serves as a contrast medium. The xenon gas rapidly dissolves in the blood and crosses the lipid-rich blood-brain barrier and enters the brain. The CBF is calculated using the modified Kety-Schmidt equation.11 After breathing the xenon and oxygen mixture, the brain is scanned. Upon completion of the scanning, the xenon is rapidly washed from the cerebral tissue (half-life about 40 seconds).
Adverse reactions include nausea, reversible altered sensorium, or respiratory depression in less than 0.1 cases. Cerebrovascular disorders are the main clinical applications of XeCT, and it has been used to study cerebrovascular physiology. Currently, XeCT is useful to determine viability of cerebral tissue globally and regionally and can be used as part of brain death criteria.
Patient Preparation and Postprocedural Care
There is no special preparation or postprocedural care required other than monitoring for any adverse reaction.
Magnetic Resonance Imaging
The second major diagnostic tool for anatomic imaging of the brain and spinal column is MRI. It is a noninvasive, painless diagnostic procedure that provides better resolution slice images of anatomic structures of the brain and other soft tissue. The technology uses strong magnetic fields rather than ionized radiation, and thus requires special, copper-lined rooms for shielding from the strong
magnetic fields created by the MRI. Current technology uses hydrogen atoms (protons) because hydrogen is the most abundant element in tissue and yields the strongest magnetic signal. The presence of thermal energy causes each proton to spin like a top.12
magnetic fields created by the MRI. Current technology uses hydrogen atoms (protons) because hydrogen is the most abundant element in tissue and yields the strongest magnetic signal. The presence of thermal energy causes each proton to spin like a top.12
MRI technology creates a strong magnetic field in which protons within the tissue align themselves in the longitudinal direction of the magnetic field.8 A computer-programmed brief (few milliseconds) burst of radiofrequency (RF) pulse is applied to the magnetic field, which changes the axis of the alignment of the atoms from the longitudinal to the transverse plane. This effect of rotating the atoms about the axes in a uniform manner is known as resonance. When the RF is turned off, the atoms return to their original alignment, an effect known as relaxation. The RF energy that was absorbed and then emitted results in an MR signal that is detected by electromagnetic receiver coils and then stored. Application of the RF is repeated several times as a pulse sequence with the signals being measured and stored after each pulse application. Depending on how quickly these atoms return to their original state, the computer can determine which kind of tissue is represented by the returned signal. It is the intensity of the returned signal reported as hypo-, iso-, or hyperintense that correlates to tissue type.13 Computer programs analyze the stored data and an image is mathematically constructed from the combined data. Table 6-2 provides basic MRI scan sequences.
The terms T1 and T2 refer to the weighted relaxation time constants for protons; these weights may be altered to highlight certain features of the tissue structure. In a T1-weighted image, the CSF appears very dark, gray matter is lighter, and white matter is bright. The cortical border and cortical-white matter junctions are well defined. In a T2-weighted image, the CSF appears white and there is poor color discrimination between gray and white matter. The T2 image highlights alterations in white matter such as infarction, demyelination, and edema.3
Pulse sequences refer to the different imaging techniques generated by manipulating the timing of the RF pulses. The pulse sequence variables, which are manipulated to produce different types of images, are known as echo time (TE) and repetition time (TR).
TABLE 6-2 BASIC MRI SCANS | ||||||||||||
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The type of image selected depends on the type of tissue under study and the suspected pathology. This ability to manipulate pulse sequence and components enhances the usefulness of MRI. Some of the more common pulse sequences include spin-echo, inversion recovery, gradient-echo, and fluid attenuation inversion recovery (FLAIR) sequences. Table 6-3 includes special MRI sequences. Each type has characteristics that make it useful in special circumstances and sequences.
Gadolinium is the paramagnetic agent used as a contrast medium for MRI studies. It enhances the process of proton relaxation during the T1 sequence of MRI, resulting in sharper definition, and highlights the surrounding regions of lesions where the blood-brain barrier has been disrupted.
Contraindications
More materials for medical use that are MRI friendly are now used in neurological and orthopedic equipments. However, it is imperative to screen patients accurately for the presence of any devices that are contraindications for MRI before scheduling the procedure. The absolute contraindications for MRI include the following.
Patients with ferromagnetic devices, such as artificial pacemakers, defibrillators, implanted stimulators of the brain or spinal cord, cochlear implants, prosthetic devices (e.g., metallic hip replacements, orthopedic pins), artificial limbs, respirators, and other metallic equipment
Patients with older ferromagnetic intracranial aneurysm clips or metal bullet or other metal fragments in the orbits or brain
Women in the first trimester of pregnancy (gadolinium contraindicated during entire pregnancy)14
Placement of a vascular stent, coil, or filter within the past 6 weeks14 The following are the relative contraindications.
Agitated, uncooperative patients or patients with uncontrolled movement disorders
Grossly obese patients who cannot fit into the MRI tube
Claustrophobic patients who cannot tolerate the closeness of the tube
Critically ill patients requiring a ventilator and IV pump (some ventilators are specially designed nonmagnetic; IV pumps are generally magnetic and cannot be used)14
Clinical Applications
Because MRIs are not obscured by bone, the technique is excellent in detecting soft tissue changes that are insensitive with CT scan. These include ischemic and infarcted areas; degenerative diseases (e.g., multiple sclerosis, Alzheimer’s disease); cerebral and spinal cord edema; hemorrhage; arteriovenous malformations; small tumors, particularly in the difficult-to-visualize areas of the brainstem, basal skull, and spinal cord; and congenital anomalies. The superb sharpness and precision of detail are superior for diagnosis and location of lesions.
Procedure
The patient is screened for contraindications. After removing all metal objects and credit cards (magnet can desensitize the black strip on the back of a credit card), the patient lies on a padded stretcher that slides into a tunnel-like chamber. The head is placed in a plastic helmet-like structure; the arms are at the side of the body and are held in place with Velcro straps. The head of the table is then rolled several feet into the scanner. The scanner tube has a restricted opening; it has been compared to the opening of a barrel or large pipe (Fig. 6-5). During
the scan, noise, caused by the pulsating RF waves, is heard. The patient must be prepared for this sound and for the requirement to remain absolutely motionless during the scan. Although the patient is alone in the room, voice contact is maintained with the technician through an intercom. If contrast enhancement is desired, gadolinium is administered intravenously. The MRI takes approximately 5 to 50 minutes to complete.
the scan, noise, caused by the pulsating RF waves, is heard. The patient must be prepared for this sound and for the requirement to remain absolutely motionless during the scan. Although the patient is alone in the room, voice contact is maintained with the technician through an intercom. If contrast enhancement is desired, gadolinium is administered intravenously. The MRI takes approximately 5 to 50 minutes to complete.
TABLE 6-3 SPECIALIZED MRI SCANS | |||||||||||||||
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