Multidetector Computed Tomography: Evaluating the Trauma Patient

Elizabeth Knoff, RT(R)

  ^*Computed Tomography Technologist, Department of Radiology, Body CT, Johns Hopkins Hospital, Baltimore, Maryland.
  Address correspondence to: Elizabeth Knoff, RT(R), Radiologic Technologist, Department of Radiology, Body CT, Johns Hopkins Hospital, 601 North Wolfe Street, Baltimore, MD 21287. E-mail: eknoff1@jhmi.edu.

Disclosure Statement: Ms Knoff reports having no significant financial or advisory relationships with corporate organizations related to this activity.

ABSTRACT

Multidetector computed tomography (MDCT) is useful in the evaluation of many anatomical parts and has become the gold standard for diagnostic imaging of trauma patients. Many of the reasons for this are related to the core strengths of MDCT: speed, specificity, and accuracy. However, there are many factors to consider when using MDCT. This article discusses implications for, as well as common findings from, the most common MDCT examinations performed on trauma patients. The use of intravenous iodinated contrast material is addressed, although a more thorough discussion of contrast usage is beyond the scope of this article. This article also discusses imaging of pediatric trauma patients, including how to balance the benefits and risks of radiation exposure, ensuring compliance from the patient during the examination, and the differences in common findings between adult and pediatric trauma patient. Common pitfalls in imaging of trauma patients and how to prevent them also are covered. Finally, this article examines the role of the computed tomography (CT) technologist in assuring high-quality diagnostic examinations, and discusses the most variable, and arguably most important, factor in trauma imaging: the CT technologist should be in control of the situation within the imaging suite at all times and be prepared to handle the unexpected and challenging circumstances that constantly occur in trauma cases. The information provided in this article is meant to assist CT technologists in this endeavor.

Introduction
In the field of emergency radiology, the most dramatic cases involve trauma patients, who have suffered severe and sometimes life-threatening injuries and require immediate treatment to prevent substantial complications. In the United States, deaths directly attributable to trauma number 100 000 annually.¹ Chest trauma alone is the leading cause of death for individuals ages 25 to 44.² In addition, there are social costs, such as disability and medical care for individuals who sustain serious, but not fatal, injuries. One study estimated that health costs and lost productivity associated with trauma resulted in costs totaling $406 billion in 2006.³ When it comes to evaluating trauma patients, multidetector computed tomography (MDCT) is a useful imaging tools for fast assessment of critical injuries. MDCT allows physicians to make faster and more accurate diagnoses of injuries sustained by the trauma patient, thus reducing the time spent treating distracting non-life-threatening injuries, and minimizing any delays in treating life-threatening injuries. This saves money by providing more efficient care to the critically injured.²

In the following sections, the most common examinations performed during initial trauma assessment are discussed, including the head, face, chest, cervical spine, abdomen, pelvis, and thoracolumbar spine. For all the examinations outlined in this article, the trauma scanning protocols provided are those commonly followed in the author's facility for an average-sized adult, but readers should understand that scanning parameters can vary widely to reflect facility standards, radiologist preferences, patient history, the current physical condition of the patient, and the facility's MDCT capabilities. In addition, important considerations in applications such as pediatric imaging and vascular imaging are presented. Finally, the role of the computed tomography (CT) technologist will be discussed to offer insight into the qualities and skills necessary in order to provide excellent patient care to patients suffering from acute trauma.

Advantages of Using MDCT to Evaluate Trauma Patients
Multidetector CT provides rapid imaging results with a high degree of specificity and accuracy and is therefore a valuable tool in the trauma setting in a variety of applications, including the examination of blunt cerebrovascular injuries, abdominal, and pelvic injuries.^4,5 The availability of MDCT in many trauma centers, combined with its ease of use, makes it an ideal modality for evaluating multitrauma patients, defined as those who suffer from injuries to multiple organs, skeletal system, or vascular system obtained during a single event, in which 1 or more of the injuries is potentially life threatening.⁶ Therefore, it is often necessary for CT technologists to be able to perform rapid scans of several areas when evaluating a multitrauma patient. CT technologists responsible for performing studies in trauma patients should also have a high level of expertise with the CT unit and a thorough understanding of possible trauma pathologies so that accurate studies can be quickly obtained and vital treatment can be initiated. MDCT allows the CT technologist to obtain images under ideal contrast opacification for all of the existing phases of enhancement—vascular, parenchymal, and excretory.⁷

The evolution of CT has progressed to the point that the modality is considered a mature technology that can be applied in a variety of clinical settings.⁸ MDCT in particular offers the rapid return of accurate images with a minimum of artifacts. Specifically, the increased speed with which examinations can be obtained with MDCT has drastically reduced artifacts caused by voluntary and involuntary motion. For example, an examination performed using single-detector computed tomography (SDCT), which would have taken minutes, will only take seconds with initial versions of MDCT.⁶ As the number of detectors has increased in recent years, so has the speed of examinations. It is now possible to scan the entire abdomen and pelvis in under 30 seconds. Faster scan times also makes it possible for the CT technologist to scan an entire anatomic area with a single breath hold, thus eliminating respiratory misregistration imaging artifacts between scans.⁹ This decrease in scan time also allows the CT technologist to obtain multiple examinations in quick succession on a single trauma patient.

Another benefit of MDCT is that CT technologists can obtain scans with greater spatial resolution than SDCT, leading to images that have more detail.⁶ Data from these scans can be manipulated to form multiplanar reformats (MPRs), which allow the physician to view anatomic information in the sagittal, coronal, oblique, or any other plane that can be produced. All these factors have contributed to the ability of the trauma radiologist to offer increasingly accurate diagnoses on trauma patients.⁷

Most importantly, MDCT provides a clear picture of the extent of physical injury present in the trauma patient, allowing the physician to address the most critical needs of the patient first, rather than focusing on the confusion or distractions that present during the clinical examination, such as neurologic impairment, drug or alcohol use, and other extenuating (but not serious) injuries.

General Considerations in MDCT Imaging Studies
The technologist must be familiar with both ideal patient positions and techniques to manipulate positioning, when necessary, in the urgent setting of trauma imaging. In fact, technologists experienced in trauma imaging should understand that not all trauma patients present in the supine position that is ideal for many studies, including those of the head, facial, or cervical spine, and considerable manipulations may be needed to accommodate these situations. This can most often be accomplished by obtaining images and then utilizing MPR to adjust the coronal, sagittal, and axial planes, so they appear to occur in true anatomical position.

The patient should also be assessed for the presence of items that could result in unwanted artifacts in the imaging study. These could range from earrings and necklaces, to braids, bras, or other items on the patient's body. Artifacts are not limited to the patient and can also include items such as large clips remaining on the backboard from the straps used during ambulance transportation of the patient. These should be removed before the examination, if possible, to reduce the level of artifacts and the time needed for examination.

In all imaging studies, communication is important with the patient to ensure his or her cooperation. Unwanted patient movements can impact the integrity of the study and should be avoided, and patients should be directed on breath holds to limit respiratory motion during chest studies. However, it is important to recognize that communication may not always be feasible, especially in patients suffering from head trauma who may be unconscious. If possible, technologists should explain to the patient that he or she should hold very still and that the examination table will be moving in and out of the gantry. These measures will ensure image quality and limit the possibility of misdiagnosis.

Assessment of Head Trauma
Trauma to the head is best visualized by MDCT, and MDCT of head trauma makes radiographic films of this area obsolete.¹⁰ Causes of head trauma include any possible injury involving the head and/or neck region; the most common causes of head trauma are motor vehicle accidents (MVAs), falls, gunshot wounds, and assault.¹¹ When physicians assess the trauma patient, any possible trauma to the head will indicate the need for a head CT examination. Other symptoms may cause suspicion of injury to the head and can also indicate the need for a head MDCT even in the absence of obvious head trauma. These symptoms include, but are not limited to, headache, vomiting, loss of consciousness, seizure, altered mental status, syncope, and loss of vision, smell, or hearing.¹¹ If it is possible, the patient's history should be obtained by the trauma physician because a history of head trauma can be the cause of cumulative neurologic deficits.¹¹

Positioning and Parameters
The overwhelming majority of patients who receive a head CT as part of their trauma assessment will be on a backboard and most will also have a cervical collar around their neck. Eliminating patient motion during the scan is of the utmost importance; if necessary, additional restraint can be implemented by taping the patient's head to the backboard or head holder attachment on the examination table. Care should be taken, however, not to apply tape directly to the patient's hair or skin, and these can be protected by lining the area to be taped with gauze or a sheet.

While scanning parameters can vary considerably depending on the facility, operator and radiologist preferences, and other factors, imaging for adult head trauma could include the scanning parameters summarized below:

• 120 kV
• Collimation of 0.6 mm
• Effective mAs level of 400
• Rotation time of 1 second
• Pitch of 1

Four planar reconstructions should be performed. Thin slices of 0.75 mm reconstructed at 0.5-mm intervals should be obtained for both the soft tissue window using the H30 kernel, and bone window using the H60 kernel. Thicker slices of 5.0 mm should be reconstructed at 5-mm intervals using the same 2 window and kernel combinations as utilized for the thin images. All images should ideally be free of motion and include anatomy from the top of the skull through the skull base.

Potential Findings
Proper imaging studies at presentation in patients with head trauma are critical and can provide valuable information to guide treatment and prognosis. For example, perfusion CT upon admission has demonstrated value in determining future functional outcomes in patients presenting with severe head trauma.¹² There are several potential findings when a head CT is performed on a trauma patient. Within the cranium, some of the findings that can be visualized are diffuse cerebral edema, subdural and epidural hematomas, focal cerebral contusion, and subarachnoid or intraparenchymal hemorrhage.¹¹ Fracture of the skull itself is a very serious injury and is ideally imaged by MDCT. There are several types of skull fractures that can be differentiated on MDCT. These include displaced and undisplaced vault fractures, stellate fractures, linear fractures, and comminuted fractures.¹⁰ Identifying skull fractures is especially important because the presence of one increases the risk of complications due to infections such as meningitis, encephalitis, or abscess, which affect the central nervous system.⁸ When a skull fracture is caused by a penetrating injury, air pockets can sometimes be seen within the cranium.¹⁰ A bleed, or acute hemorrhage, is a serious condition, which is visualized as a hyperdense area in one of the following cranial compartments: intra-parenchymal, subdural, extradural, or subarachnoid.¹⁰

Assessment of Facial Trauma
Similar to head trauma, trauma to the face is most often the result of an MVA, assault, fall, or gunshot wound.¹³ CT is essential in facial trauma, even more so than radiography, because CT can provide detailed soft tissue and bony anatomy images. In fact, MDCT provides better accuracy and specificity than a combination of radiography and clinical examination.¹³ Facial imaging with MDCT is usually only indicated when there is a strong suspicion of fracture. It may also be indicated when facial fractures are an incidental finding on imaging of the head and require a greater degree of spatial resolution. The images obtained from facial MDCT can determine the extent, direction, and displacement of a facial fracture.¹³ The only exception to this rule occurs with fractures of the mandible, which are better demonstrated by a panorex examination. Three-dimensional reformations of the mandible can be useful in evaluating fractures; however, for initial detection, panorex examination is still preferred. Fractures of different facial structures result from varying forces applied to the face. Fractures of the maxillary bone are commonly caused by an upward blow, whereas fractures of the bony structures surrounding the frontal sinus commonly result from a direct blow to that area.¹³

Positioning and Parameters
Similar to patients with head trauma, those presenting with facial trauma should ideally be supine on the examination table for an MDCT examination. Compared to other forms of imaging, MDCT covers all of the facial anatomy superiorly from the top of the frontal sinuses inferiorly through the mandible. The tip of the nose anteriorly is scanned through the entire temporomandibular joint posteriorly.

While scanning parameters can vary considerably depending on the facility, operator and radiologist preferences, and other factors, imaging for facial trauma could include the scanning parameters summarized below:

• 120 kV
• Collimation of 0.6 mm
• Effective mAs level of 400
• Rotation time of 1 second
• Pitch of 1

Several reconstructions are made when scanning the face. Images with 3-mm slice thickness are reconstructed at 3-mm intervals for the soft tissue window using the H30 kernel and the bone window using the H70 kernel. Thinner slices of 0.75 mm are reconstructed at 0.5-mm intervals for both the soft tissue window using the H30 kernel and the bone window using the H60 kernel. Sagittal and coronal MPRs are performed in both bone and soft tissue windows. The soft tissue windows are useful in facial imaging because mucosal thickening and/or the presence of air-fluid levels in the sinuses can suggest the presence of fractures.¹³

Potential Findings
Fractures of the face are the most common clinically significant finding on facial MDCT examinations. The most common systems for classifying facial fractures involve defining the anatomy involved and describing the mechanism of injury as low-, middle-, or high-energy.¹³ The mechanism of injury classifications refers to the amount of energy transferred by the source of injury to the face during the event. For example, a fall from standing height could cause a low-energy injury, whereas a high-speed motor vehicle collision could cause a high-energy injury when the person's face strikes the dashboard. Although fractures of the nasal bone comprise approximately 50% of all facial fractures, the structures most often visualized as fractured in MDCT include the anterior and posterolateral maxillary sinus walls, the zygomatic arch, and the lateral orbital wall.¹³ When evaluating MDCT images for facial fracture, injury to the soft tissues can also be evaluated. Common areas of soft tissue injury involved in facial fracture include the orbital globe and the intracranial contents located immediately posterior to the frontal sinuses (Figures 1 and 2).¹³

Assessment of Cervical Spine Trauma
Evaluating cervical spine trauma is one of the true strengths of MDCT in the trauma setting. While cervical spine fractures are sometimes not apparent on plain radiographs, MDCT well visualizes most of these fractures.¹⁴ Its superiority when imaging cervical spine fractures is evidenced by the fact that the sensitivity for detection of cervical spine fracture using CT is 90% to 99%, whereas its specificity is 72% to 89%.¹⁵ Both trauma- and non-trauma-related incidental findings are also common in trauma patients undergoing CT of the cervical spine, and should be noted so that patients can be appropriately treated, if necessary.¹⁶ Imaging with spiral CT has also been shown to reveal potentially serious incidental findings in a mixed trauma population.¹⁷ The seriousness of cervical spine injuries makes quality imaging vital for the potential patient. Cervical spine injuries produce some form of neurologic deficit in 40% to 50% of patients who sustain them. These deficits range from severe to fatal, therefore early detection and treatment is of the essence.³ Patients who have experienced high-energy trauma, sustain injury to the head, or who exhibit neurologic deficits are all prime candidates for MDCT imaging of the cervical spine.¹⁴ Cervical spine trauma is commonly caused by injuries to the head, and the most common cause of cervical spine trauma is MVAs.¹⁵ Patients suffering from cervical spine injury can exhibit symptoms including, but not limited to, neck pain, pain in the upper limbs, facial pain (especially in the jaw), headache, paresthesia, and neck stiffness.¹⁵

Positioning and Parameters
When imaging the patient with suspected cervical spine trauma, the patient will most likely be supine on a backboard with a cervical collar around his or her neck. Unfortunately, the cervical collar is not always ideally placed, and therefore, the patient's positioning may not be perfect in all cases. In these instances, it is extremely important the CT technologist does not remove the cervical collar in an attempt to reposition the head and neck. Trauma patients are unpredictable in their behavior, making removal of any restraint protecting the spine dangerous at best, and it is not within the CT technologist's scope of practice to apply torquing pressure to the spine of a trauma patient. This would endanger the safety of the patient and could lead to further injury. To compensate for this, the CT technologist may horizontally and gently slide the patient into a better position, and then use software applications when performing MPRs to obtain "straighter" images of the spine for the trauma neuroradiologist.

While scanning parameters can vary considerably depending on the facility, operator and radiologist preferences, and other factors, imaging for cervical spine trauma could include the scanning parameters summarized below:

• 120 kV
• Collimation of 0.6 mm
• Effective mAs level of 400
• Rotation time of 1 second
• Pitch of 1

The reconstructions should include a 2-mm slice thickness reconstructed at a 2-mm interval for both the soft tissue window using the H30 kernel and the bone window using the H60 kernel. Thinner images are obtained with a 0.75-mm slice thickness reconstructed at 0.5-mm intervals for the above mentioned window/kernel combinations. Sagittal and coronal MPRs are obtained in the bone window.

Potential Findings
Fractures and whiplash injuries are the most commonly visualized injuries in CT of the cervical spine (Figures 3 and 4).¹⁵ A whiplash injury will alter the curvature of the cervical spine, which is naturally lordotic. This alteration can run the range from slight to almost a full inversion of the curvature of the cervical spine. Whiplash injuries occur when the neck is first hyperflexed and then hyperextended by an external impact.¹⁵ In the case of cervical spine fractures, MDCT can visualize the position of fragments of fractured vertebrae in multiple planes, and can determine the presence of damage to the spinal canal that these vertebrae protect.¹⁴ For imaging of the cervical spine in trauma patients, MDCT has greater specificity, sensitivity, and speed than plain film radiography.¹⁴

Assessment of Chest Trauma
All trauma is serious, but trauma to the chest is especially serious due to the close proximity of vital organs, such as the heart and lungs. Combined with the fact that the aorta begins and descends through this region, the potential severity of chest trauma makes sense. In the trauma patient population, blunt thoracic trauma is directly responsible for 20% to 25% of all fatalities, and is a major complicating factor in an additional 50% of trauma-related deaths.² There are many causes for chest trauma, the most common being MVAs and falls.² Other causes of chest trauma include, but are not limited to, assaults, gunshot wounds, stabbings, and sports-related injuries. There are 3 main mechanisms of blunt force trauma to the chest, the most common form of injury to the chest. The first is direct impact to the chest, which can be caused by an MVA, fall, or a direct blow to the chest. The second is thoracic compression, which is the result of body tissues striking a fixed bony object. Lastly, deceleration injury, which is an injury caused when a person stops suddenly.²

Positioning and Parameters
When imaging the patient for chest trauma, the arms should be raised above the head of the supine patient. However, patients do not always present in the supine position and it is not always possible to raise a patient's arms, especially in cases involving fracture of the humerus and/or shoulder girdle. In such cases, the arm should be straightened as much as possible to lie along the length of the body, and scanning technique may be increased, depending on the size of the patient. Again, the CT technologist should be diligent in checking for potential artifacts, including (but not limited to) necklaces, backboard straps, suspenders, and zippers from cut off clothing. Communication with the patient during the examination is vitally important because most chest CT examinations can be completed with a single breath hold, as long as the patient is cooperative. For patients who are intubated and whose breathing is being controlled by a mechanical breathing apparatus, teamwork with the respiratory therapist or in some instances an anesthesiologist or nurse anesthetist can accomplish the same outcome. Scanning should cover the area from the apices through the bases of the lungs, often with the adrenals being the last anatomy scanned at the inferior aspect of the scan.

While scanning parameters can vary considerably depending on the facility, operator and radiologist preferences, and other factors, imaging for chest trauma could include the scanning parameters summarized below:

• 120 kV
• Collimation of 0.6 mm
• Effective mAs level of 250
• Rotation time of 0.37 seconds
• Pitch of 0.5

An injection of 100 to 120 mL of iodinated intravenous (IV) contrast is administered (in the absence of contraindication), and scanning is performed in the portal venous phase or 55 to 60 seconds after the injection begins. An injection rate of 2 mL per second is standard for routine trauma assessment. Images are reconstructed using soft tissue, bone, and lung windows. In the soft tissue window, images are reconstructed using 5-mm slice thickness with 5-mm intervals and a B30 kernel. Additional thinner images are obtained in the soft tissue window by setting a 1.5-mm slice thickness at a 1-mm reconstruction interval using the B20 kernel. In the lung window, images are generated using a 3-mm slice thickness reconstructed at a 3-mm interval using the B80 kernel. The bone window reconstructions are generated using a 3-mm slice thickness at 3-mm intervals using the B70 kernel. Sagittal and coronal MPRs are obtained using the soft tissue window.

Potential Findings
Significant findings seen in CT of chest trauma can include pneumothorax, hemothorax, injuries to the aorta, hemorrhage of the mediastinum, and airway or diaphragm injuries (Figure 5).² Direct impact to the chest can lead to fractures of the ribs and sternum, sternoclavicular joint dislocation, or vascular injuries (Figure 6).² Thoracic compression can cause organ rupture or hemorrhage. Deceleration injuries can lead to injuries of the thoracic aorta or major aortic branches.²

Assessment of the Abdomen and Pelvis
Blunt trauma is the major cause of injury to the abdomen and pelvis in trauma patients. These 2 anatomical regions are grouped together and scanned as 1 examination for several reasons. This grouping provides continuity in imaging of bowel and vascular structures throughout the region, as the contents of the abdominal cavity can lead to collection of free fluid in the pelvic cavity. Therefore, imaging both areas at once provides a more complete assessment of the extent of the injury. Abdomen, pelvis, and lumbar spine CT imaging may be important in detecting otherwise missed injuries in blunt trauma. One study reported that compared with a selective algorithm based on suspicious findings, routine CT imaging in blunt trauma patients detected additional injuries to the abdomen in 15%, injuries to the pelvis in 2.4%, and injuries to the lumbar spine in 8.2% of evaluated patients.¹⁸

The most commonly injured organs in abdominal trauma are the spleen and the liver.⁵ CT has such a high degree of accuracy in diagnosing renal injury, it has essentially replaced the IV pyelogram for assessment of injury in many parts of the country.⁵ Other rarer injuries can also be assessed at the same time without any additional radiation exposure. For example, gallbladder injury, which occurs in 2% to 8% of trauma patients, as well as bowel/mesenteric injury, which occurs in 0.3% to 1.1% of trauma patients, can both be assessed using MDCT.⁷

Positioning and Parameters
The blunt trauma patient is often imaged supine with the arms above the head, when possible. However, technologists should understand that patients may present in a variety of positions depending on the nature of the trauma and should be able to adjust the imaging environment to accommodate unique presentations. If communication with the patient is possible, the patient should be instructed to suspend respiration during the examination.

While scanning parameters can vary considerably depending on the facility, operator and radiologist preferences, and other factors, imaging for abdomen and pelvis trauma could include the scanning parameters summarized below:

• 120 kV
• Collimation of 0.6 mm
• Effective mAs levels of 250
• Rotation time of 0.37 seconds
• Pitch of 0.5

Routine trauma assessment often includes an injection of 100 to 120 mL of IV iodinated contrast material at a rate of 2 to 3 mL per second. Scanning commences 55 to 60 seconds after the start of the injection to ensure complete portal venous enhancement, and includes the anatomic area from the diaphragm of the lung through the bottom of the pelvis. Several reconstructions are generated using imaging data. Images with a 5-mm slice thickness are reconstructed at 5-mm intervals in the soft tissue window using the B30 kernel. Thinner images are also reconstructed in the soft tissue window using a 1.5-mm slice thickness at 1-mm intervals using the B30 kernel. Images of 3-mm slice thickness are reconstructed at 3-mm intervals in both the lung window using the B80 kernel and bone window using the B70 kernel. In addition, sagittal and coronal MPRs are generated in the soft tissue window.

Potential Findings
There are many different attenuation values that will be seen in abdominal MDCT. It is important to recognize which values represent normal anatomy and which are indicative of pathology. Fluid with an attenuation of less than 0 HU is indicative of bile, 0 to 15 HU indicates ascites or urine, and 20 to 40 HU indicates free intraperitoneal blood.⁷ A site of active bleeding is demonstrated by an area of enhancement that has an HU value within 10 HU of an adjacent opacified blood vessel.⁷ When intraperitoneal fluid is seen, this indicates an injury to an organ, the bowel, or the mesentery.⁷ Common injuries of solid organs include contusions, lacerations, hematomas, and active extravasation.⁷ Injuries to the spleen and liver, both being extremely vascular, are considered very serious and MDCT allows lesions in these areas to be correctly identified and proper treatment to be planned.

Assessment of Trauma to the Thoracolumbar Spine
When trauma to the thoracolumbar spine is suspected, imaging for this area is usually accomplished by means of retrospective reconstructions taken from data acquired during a chest/abdomen/pelvis combination examination. Because of its proximity to vital organs, trauma causing damage to the thoracolumbar spine is rarely isolated. In cases of blunt trauma, 2% to 3% of patients will have a thoracic and/or lumbar spine injury. Of these, 40% to 50% will suffer from some form of neurologic deficit.¹⁵ Therefore, if any suspicion for spinal injury is present, and MDCT imaging of the chest, abdomen, and pelvis is already taking place, it is reasonable to take the time to reconstruct thoracolumbar images because there is no additional radiation impact to the patient.

Parameters
While scanning parameters can vary considerably depending on the facility, operator and radiologist preferences, and other factors, imaging for trauma to the thoracolumbar spine could include the scanning parameters summarized below:

• 120 kV
• Collimation of 0.6 mm
• Effective mAs level of 350
• Rotation time of 1 seconds
• Pitch of 0.7

The reconstructions performed for the thoracolumbar spine include images of 3-mm slice thickness with a 3-mm reconstruction interval obtained for both the bone window (using the B70 kernel) and the soft tissue window (using the B30 kernel). Thinner slices of 0.75-mm with reconstruction intervals of 0.5-mm are obtained again in both the bone window (using the B60 kernel) and the soft tissue window (using the B20 kernel). Multiplanar sagittal and coronal images are also obtained using the bone window. In some rare instances, the physician may also request MPRs in the soft tissue window.

The most common finding on MDCT images that are positive for pathology is fracture. MDCT has demonstrated better detection and characterization of fractures of the thoracolumbar spine than plain radiography, especially in the areas of the posterior elements of vertebrae, malalignment of vertebrae, and visualizing fragments in the intracanalicular space.¹⁵

Use of MDCT for Vasculature Imaging
Multidetector CT of vasculature in trauma patients proves its worth most when evaluating injuries to the thoracic and/or abdominal aorta. Although vascular injury from blunt trauma is relatively rare—occurring in less than 1% of all trauma patients—these injuries are a source of fatalities in the trauma setting. Thus, the faster diagnostic abilities of MDCT make it truly a life-saving tool.² MDCT angiography has proven it is superior to traditional angiography, and it is now the imaging modality of choice for many physicians for evaluating vascular injury.⁹ The indications for performing vascular MDCT are as varied as the different regions that could be examined with this technique. One common indication, which spans any possible anatomic region, is the existence of a penetrating trauma adjacent to any significant blood vessel.¹⁵ Other injuries requiring vascular MDCT include major blunt cervical spine trauma, penetrating trauma (eg, stab wounds), and deceleration chest injuries.^2,15 The stroke patient represents a special case for vascular MDCT. When a person sustaining head trauma also suffers from a stroke, an examination of the carotids should always be performed to assess for any vascular injury.¹¹ This examination would be in addition to a non-contrast MDCT examination of the head. When performing vascular studies of the carotids and head, it is important to first obtain an examination without contrast to assess for intracranial hemorrhage before administering contrast.

Although the scope of this article does not permit discussion of every unique vascular examination, some themes common to all vascular examinations are important to note. IV iodinated contrast material is required for all vascular examinations except a bleed. The goal for injection is to push a bolus of contrast material fast enough to opacify the major arterial vessels of a section of anatomy without allowing contrast material to permeate the parenchyma of an area. Therefore, an injection rate of 3 to 5 mL per second is required for all vascular examinations. A patent peripheral IV that is at least 20 gauge in size is ideal for this examination.

In addition, timing of the scan is a vital component in performing optimal vascular examinations, and is accomplished in 1 of 2 ways. The first method is to set a scan delay. This requires the CT technologist to know the average time for peak arterial opacification of an area. The second method is to use a tool called bolus tracking. With this method, an anatomic area is scanned in a single slice, and a trigger region of interest (ROI) is set on a blood vessel of known relation to the scan area. Once the injection is started, the scanner will begin scanning the same single slice until the ROI has reached the peak opacification for a given examination, at which time the scanner automatically performs the examination. The tracking allows CT technologists a variable, in that it tracks the actual flow of contrast material as opposed to setting a time when the contrast enhancement will theoretically be ideal, yet both methods are equally accurate in the hands of an experienced CT technologist.

MDCT in Pediatric Trauma Patients
In pediatric trauma, the most common form of injury is head trauma. This form of trauma accounts for 80% of deaths in pediatric trauma cases, yet less than 10% of all head scans performed on pediatric trauma cases are positive for pathology.¹⁰ When one considers the fact that these patients are more radiosensitive than other patient populations, the debate over pediatric imaging becomes clear. The ALARA concept, which stands for as low as reasonably achievable, is the standard that all radiologic technology professionals follow. This concept limits the number of examinations routinely performed on pediatric patients and limits radiation exposure by adjusting scanning parameters according to patient size.¹⁹ Included in this concept is the protection of unborn patients by screening all female patients of childbearing age for pregnancy prior to performing any study involving radiation exposure. In one retrospective study, which examined the repeat rates of examinations of pediatric patients, it was discovered that 9% of patients who were transferred with MDCT examinations needed to have these examinations repeated, with the reason for most of the repeated examinations being an inadequate initial scan.¹⁹ This amount of inadequate scanning is unacceptable in any patient population. Therefore, the CT technologist must be especially vigilant when scanning pediatric patients to ensure quality examinations are obtained during the first examination. Taking the extra time to make a pediatric patient comfortable or to explain the ease of the examination process can make all the difference.

When IV contrast is required for a pediatric MDCT examination, adult doses of contrast should not be administered. Instead, the pediatric patient is dosed using the following formula: 1 mL per pound, or 2 mL per kilogram. The upper limit for dosing IV contrast is 100 to 120 mL for cases in which the pediatric patient's weight may indicate a higher contrast dose.

Common MDCT Pitfalls
There are several common pitfalls that can negatively impact the quality of MDCT examinations. Motion is the most common pitfall in evaluating trauma patients because many are in pain or an altered state of mind. Motion causes blurring and distortion of the MDCT images, and can be avoided through proper communication with and restraint of the patient. Patient identification can also be a pitfall because imaging patients under the wrong identifiers leads to misdiagnosis and mistreatment of trauma patients. A time-out procedure, which verifies the patient name and medical record number (or date of birth), as well as the imaging procedure being performed, should be completed before any new patient is scanned. This ensures that the proper examination is being performed on the proper patient, which also reduces radiation exposure from repeat scanning. Poor IV access can be a challenging pitfall in MDCT examinations because obtaining IV access in trauma patients can be difficult due to positioning. Trauma patients may have decreased IV access due to fractures, active bleeding, or poor vein patency. Poor IV access can lead to extravasation of iodinated contrast material, which not only prevents proper opacification of vascular structures, but can also cause necrosis to the area of the extravasation. Every IV should be checked prior to injection of iodinated contrast material with an injection of at least 10 mL of saline. Any IV that does not seem adequate for injection should not be used, and new IV access must be obtained. Patient positioning is key during trauma radiography, yet this can be one of the hardest pitfalls to avoid. Injuries can prevent ideal patient positioning but patient limitations must be respected because forcing any part of the anatomy into position can have very harmful effects on the trauma patient. As mentioned earlier in this article, every attempt should be made to remove all sources of artifact from the scanning area in order to ensure accurate imaging.

The Role of the CT Technologist in Trauma
The role of the CT technologist is simple: to scan the patient correctly the first time. This sounds straightforward, but working with trauma patients can be anything but easy. Communication with the patient must be open and calm at all times. Patients respond well to empathy, and making statements of understanding prior to giving instructions can drastically increase patient cooperation with the instructions. When giving instructions to a patient, statements should be made in a clear voice and given at a steady pace. Tell the patient what is going to happen to them before it happens so there are no surprises. Workflow is also an important consideration for the CT technologist. There should be an established flow for performing examinations on the trauma patient before the patient enters the CT department. Patients need to be moved to the examination table, positioned, have a topogram or scanogram performed, IV access checked for patency, injected with IV contrast (if necessary), scanned for necessary scans, and moved back onto their stretcher. Each CT technologist/team should determine the workflow that works best for them. This leads to teamwork, which is essential when dealing with the trauma patient. The CT technologist should be proficient and knowledgeable about how to obtain individual and multiple scans on the trauma patient. This ensures quality images will be obtained for every examination even under less than ideal circumstances. Flexibility in dealing with trauma patients allows you to put patients at ease and create a more relaxed atmosphere, which increases patient compliance with examinations. In conclusion, the CT technologist is often the deciding factor in whether accurate imaging is obtained on the trauma patient.

Acknowledgement
The author acknowledges editorial assistance from Kristina Woodworth, a medical writer working with eRADIMAGING.  The author made substantial contributions to the intellectual content of the article by conceiving and designing the content, researching references and studies, drafting the manuscript, reviewing and revising the manuscript, and/or providing supervision.

References
1. Mayberry JC. Imaging in thoracic trauma: the trauma surgeon's perspective. J Thorac Imaging. 2000;15:76-86.

2. Scaglione M, Pinto A, Pedrosa I, et al. Multi-detector computed tomography and blunt chest trauma. Eur J Radiol. 2008;65:377-388.

3. Finkelstein EA, Corso PS, Miller TR. The Incidence and Economic Burden of Injuries in the United States. New York, NY: Oxford University Press; 2006.

4. Weishaupt D, Grozaj AM, Willmann JK, et al. Traumatic injuries: imaging of abdominal and pelvic injuries. Eur Radiol. 2002;12:1295-1311.

5. Sliker CW, Shanmuganathan K, Mirvis SE. Diagnosis of blunt cerebrovascular injuries with 16-MDCT: accuracy of whole-body MDCT compared with neck MDCT angiography. AJR Am J Roentgenol. 2008;190:790-799.

6. Philipp MO, Kubin K, Hormann M, Metz VM. Radiological emergency room management with emphasis on multidetector-row CT. Eur J Radiol. 2003;48:2-4.

7. Miller LA, Shanmuganathan K. Multidetector CT evaluation of abdominal trauma. Radiol Clin North Am. 2005;43:1079-1095.

8. Kalender WA. CT: the unexpected evolution of an imaging modality. Eur Radiol. 2005;15 (suppl 4):D21-24.

9. Novelline RA, Rhea JT, Rao PM, Stuk JL. Helical CT in emergency radiology. Radiology. 1999;213:321-339.

10. Tang PH, Lim CCT. Imaging of accidental paediatric head trauma. Pediatr Radiol. 2009;39:438-446.

11. Ko DY. Clinical evaluation of patients with head trauma. Neuroimaging Clin N Am. 2002;12:165-174.

12. Wintermark M, van Melle G, Schnyder P, et al. Admission perfusion CT: prognostic value in patients with severe head trauma. Radiology. 2004;232:211-220.

13. Sun JK, LeMay DR. Imaging of facial trauma. Neuroimaging Clin N Am. 2002;12:295-309.

14. Blackmore CC, Mann FA, Wilson AJ. Helical CT in the primary trauma evaluation of the cervical spine: an evidence-based approach. Skeletal Radiol. 2000;29:632-639.

15. Bagley LJ. Imaging of spinal trauma. Radiol Clin N Am. 2006;44:1-12.

16. Barboza R, Fox JH, Shaffer LET, et al. Incidental findings in the cervical spine at CT for trauma evaluation. Am J Radiol. 2009;192:725-729.

17. Deunk J, Brink M, Dekker HM, et al. Routine versus selective computed tomography of the abdomen, pelvis, and lumbar spine in blunt trauma: a prospective evaluation. J Trauma. 2009;66:1108-1117.

18. Barrett TW, Schierling M, Zhou C, et al. Prevalence of incidental findings in trauma patients detected by computed tomography imaging. Am J Emerg Med. 2009;27:428-435.

19. Fenton SJ, Hansen KW, Meyers RL, et al. CT scan and the pediatric trauma patient- are we overdoing it? J Pediatr Surg. 2004;39:1877-1881.

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