3D Imaging: Case Studies in Advanced Imaging

Christy Mutchler, RT(R)(CT)


  *Director of Laboratory Operations, 3DR Laboratories, Louisville, Kentucky.
  Address correspondence to: Christy Mutchler, RT(R)(CT), Director of Laboratory Operations, 3DR Laboratories, 332 W Broadway 15th Floor, Suite 1600, Louisville, KY 40202. E-mail: cmutchler@3drinc.com.

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

ABSTRACT

Three-dimensional (3D) imaging results in highly impressive images that clearly depict internal anatomic structures and can provide diagnostic information beyond what is available in other radiologic imaging modalities. However, the postprocessing image reconstruction needed to create these studies can require considerable staff resources and advanced training. A host of radiologic technologists have taken on the challenge of the additional training needed for 3D image reconstruction and postprocessing, and now serve as resident 3D technologist experts, either within their facility or as staff members of laboratories that specifically provide 3D postprocessing to radiology facilities that are interested in providing 3D imaging services, but are unable to maintain the staff resources to keep up with the demands required for regular postprocessing. 3D imaging has demonstrated value as an important diagnostic tool in a variety of applications in orthopedic and cardiovascular medicine. The growing field of 3D imaging demonstrates the need for advanced 3D training for radiologic technologists, so that these professionals provide consistent quality and are given the support they need in their daily work. This article will describe the current role of 3D technologists, discuss the different challenges presented with onsite or outsourced 3D postprocessing, and present relevant case studies in a variety of medical applications currently aided by 3D postprocessing.

Introduction
As the field of medical imaging advances, hospitals, clinics, and other providers of imaging services are finding that their resources stretched to the limits in an effort to provide the latest modalities. This has been especially true for 3-dimensional (3D) computed tomography (CT) imaging, which has demonstrated a great deal of value in a variety of medical specialties, including orthopedic,1 cardiovascular, and neurologic applications. Volumetric imaging has also been valuable in offering advanced illustrations for medical textbooks and surgery manuals.2 3D CT imaging and volumetric reconstruction requires a trained, dedicated staff of 3D technologists and radiologists who are able to reliably perform the postprocessing image reconstruction for diagnostic evaluation. Consequently, facilities offering 3D imaging services have the option of performing postprocessing in house, or recruiting the services of external laboratories that are entirely devoted to 3D image reconstruction, with a team of highly trained 3D technologists and other professionals. Whether 3D image reconstruction is performed in house or by dedicated outsourcing facilities, it is clear that the advanced training required for 3D image reconstruction should be credentialed with a standardized, accredited training program for these professionals. This article will review the value of 3D imaging and the 3D technologists that provide these services in a variety of clinical applications, and will discuss the need for professional credentialing to standardize the field and recognize the importance of 3D technologists in the current imaging environment.

Why Are Expert 3D Technologists Necessary?
Many busy radiology facilities are challenged by the scheduling constraints that already push their staffing capabilities to the limits, and wonder if they can take on the additional responsibility of providing 3D postprocessing reconstruction services. Although some imaging applications can be reconstructed by available radiology staff, with a minimal impact on facility workload, applications such as 3D coronary imaging may require a team of trained 3D technologists whose skills and services are devoted to 3D imaging reconstruction. Consequently, specialized facilities are now available that exclusively provide support for outsourced postprocessing and 3D image reconstruction services, freeing radiology facilities to concentrate on their core competencies.

The Role of 3D Technologists
Facilities providing specialized image postprocessing and 3D reconstruction services rely on the expertise of 3D technologists, or radiologic technologists who have received advanced training in 3D imaging. These professionals assist radiologists in diagnosis workflow, which reduces the reading and report turnaround times dedicated to each study. Importantly, 3D technologists can provide specific expertise that reduces the burden of other staff members. An advanced understanding of how 3D software works is especially important when working in an advanced postprocessing environment because specific features of anatomy and pathology can be easily misinterpreted. For example, in coronary imaging studies, atherosclerotic plaque can be hidden in the 3D volume and curved views depending on which angle the image was captured, and the size of the anatomy can also be misrepresented. An advanced knowledge of how scans are acquired and how to manipulate images gives a 3D technologist the skill to reconstruct the anatomy and pathology in multiple views. It is important for the imaging technologist to display any anatomy or pathology objectively, as this allows the reading clinician to provide an accurate diagnosis and determine whether any subjective pathology or disease requires further imaging.

Three-dimensional technologists also provide workflow consistency and promote the quality of control of facility protocols. Overall, the ability to outsource 3D postprocessing services through the use of facilities staffed by dedicated 3D technologists benefits the radiologist, referring clinician, and patient.

Providing 3D Imaging Services: Hospitals vs Outsourced Laboratories
Imaging facilities that hope to provide 3D imaging services must make a series of important decisions that could impact their desire to pursue this option. For instance, facilities must determine which staff members, including technologists, residents, or radiologists, are going to be responsible for postprocessing image reconstruction. The facility must also estimate the extent to which investments in new workstations, scanners, or other system upgrades will be necessary to support 3D services. In addition, information technology infrastructure is another important consideration, especially if the facility anticipates a need to update older systems. The impact of 3D services on daily workflow is clearly another hurdle that needs to be overcome before 3D services are implemented. Finally, and most importantly, staff training and education are critical to providing 3D imaging services.

In light of these challenges, it is clear that hospital facilities providing advanced 3D imaging services need to demonstrate consistent and strict quality control. These facilities also need to retain highly educated technologists, and should always anticipate being on the leading edge of technologic advances in the industry. In addition, these facilities need to focus on patient throughput, and need to seamlessly integrate their services into the larger hospital or clinic environment. Facilities facing staff, budget, and workflow limitations may decide to outsource 3D image postprocessing services, which could limit internal burdens and still provide the facility with the ability to offer 3D imaging services.

Case Studies and Practical Applications
Three-dimensional imaging has proven to be a valuable tool in a variety of clinical applications because of its ability to provide additional diagnostic information that was previously unavailable or difficult to obtain with 2-dimensional (2D) images. Trained 3D technologists must therefore be versed in the technology and the different techniques used depending on the anatomical structure of interest. The power of 3D imaging lies in the ability to better visualize the physical structure of the anatomy under evaluation with the addition of the azimuthal, or z-plane, in addition to the x- and y-axis views that are available in 2D imaging. The z-plane provides a rotational view around the x- and y-axis that results in a volumetrically rendered 3D view.3 Therefore, the addition of the z-plane view could result in an image that conveys a more accurate representation of the patient's anatomy. In some clinical applications, this 3D perspective could result in a more accurate and timely diagnosis. The availability of 3D imaging can also assist in preoperative and postoperative planning in surgical applications, and can also help improve the visualization and quantification of a medical issue under evaluation. In the following series of case studies and descriptions of practical use, real-world applications for 3D imaging will be presented and discussed.

However, before delving into these discussions, it is important to review the postprocessing terminology commonly employed in daily practice:

Figure 1Figure 2Orthopedic Diagnostics
In the orthopedic setting, 3D imaging can be an important tool for assessing trauma patients, including total 3D body imaging in those who are suspected of having sustained multiple internal traumas. As such, the use of 3D imaging in orthopedic trauma can allow for more intuitive presurgical planning and detect occult fractures that may not otherwise be found upon initial examination (Figure 1). Postprocessing segmentation is particularly important in orthopedic 3D applications because it eliminates any image confusion due to superimposition (Figure 2), provides clinicians with additional diagnostic information, and assists in preoperative planning. In the trauma setting, multiplanar CT and 3D CT reconstruction can help surgeons better visualize the extent of a patient's injuries.1

Case study #1: Hip impingement
A 37-year-old female presented with chronic right hip pain. After being diagnosed with impingement, the patient was preoperatively scanned to plan for surgery. By performing a CT scan with 3D reconstruction, the patient's specific anatomy can provide the orthopedic surgeon with detailed information needed to prepare for surgery, beyond a standard radiographic film.

Impingement, along with hip dysplasia and avascular necrosis, involves the femoral head and how it functions in the socket of the acetabulum. To show this relationship, the 3D technologist obtained bone images that were segmented out to show each part's surface detail (Figures 3 and 4). The CT data were also manipulated with MPRs, volume renderings, and CPRs (Figure 5).

Figure 3

Figure 4Figure 5

 

With no patient interaction and limited history, it is the technologist's responsibility to provide the appropriate reconstructions that fit the presenting pathology and diagnosis. A 3D technologist is trained to recognize the important images that would be helpful to a clinician for diagnosis or a subsequent surgical procedure. Patients should be encouraged to review and discuss their images with their clinician, within the context of their diagnosis and treatment plan.

Figure 6Figure 7These volume rendered images, or real 3D images, are just pretty pictures without the image processing that makes them important diagnostic tools. MPR images are not immediately illustrative to the layman, but are very useful to the clinician. These reformats can depict the anatomy in its true position even if the patient was not scanned in that position. For instance, the orthogonal planes can be manipulated to represent this anatomy. In Figure 6, the green line is oblique to align parallel to the surgical neck of the femur. In Figure 7, the oblique coronal view clearly shows the femoroacetabular joint.

Hip arthroscopy is a less invasive surgery to repair labral tears, damaged cartilage, and reshaping of the femoral head. Reconstructed 3D images have changed the way arthroscopic surgery is practiced. The clinician can now have the foresight of the anatomy before the surgery takes place. The images can also be used intraoperatively to help the clinician navigate the patient's anatomy during surgery. More importantly, hip arthroscopy can delay or sometimes prevent the need for a total hip replacement.

Advanced diagnostics for orthopedic fractures
Multiplanar reformats have been a standard alternative view for visualizing anatomy aside from the axial scanned raw data. 3D imaging, with the addition of the z-plane perspective, provides radiologists with coronal, sagittal, axial, and oblique views that can provide additional diagnostic information beyond traditional imaging that only includes axial views.3 These advanced 2D views aide in diagnosing complex fractures and other anomalies that are not well defined in the axial slices. In 3D applications, MPRs and volume rendered images are routine reconstructions for orthopedic scans. There are numerous other rendering techniques that can display the anatomy and pathology in orthopedic applications. For instance, when a patient has had an open reduction internal fixation, the hardware can be displayed in an inverse 3D MIP (Figure 8a). The hardware can be seen through the translucent bone, and these images can verify the alignment of rods and screws. In addition, colormaps (Figure 8b) can be made to provide additional diagnostic information to the referring clinician.

Figure 8

When performing 3D imaging procedures, adjustments in window width and level can result in clearer views of various anatomical structures. These adjustments are useful when tumors or masses have invaded tissue or when penetrating trauma is present. When patients are scanned, all the anatomy acquired in the field of view is assigned a 2D gray scale HU. Windowing can help postprocessing technologists choose what is displayed and what is not displayed. The less dense anatomy can be excluded from the area of interest with windowing techniques that suppress a certain set of voxel values to subjectively remove anatomical data that are not of interest in the imaging study.4 As a result, the less dense anatomy appears transparent in the image (Figure 9).

Figure 9

Case study #2: Monolateral Lisfranc fracture
After landing awkwardly from a stunt, a 24-year-old cheerleader was sent for imaging. It was determined that the patient had suffered fractures and dislocations. Multiplanar imaging reformats demonstrated that these fractures and dislocations were consistent with a monolateral Lisfranc fracture (Figure 10). This type of fracture dislocation is the disarticulation between the midfoot and forefoot, which is held together by the Lisfranc ligament. Additional 3D imaging (Figure 11) visually solidified this diagnosis and accurately determined the location of the fractures and dislocations, which was important information for the orthopedic surgeon prior to surgery. Although this type of injury is uncommon, it is important that it is promptly recognized and appropriately treated.

Figure 10

Figure 11

Neurologic Applications
CT angiography
Computed tomography angiography (CTA) is a specific type of CT that can quickly evaluate the arterial system and offers a noninvasive, timesaving alternative to the conventional catheter arteriogram. Stroke patients in particular have benefited from this scanning technique, which can reveal diseased vessels, morphology of plaque, cerebrovascular accident, and the source of the ischemia. When a patient arrives at the emergency department with a variety of symptoms, including blurred vision, headache, slurred speech, or weakness on one side of the body, it is important to arrive at a rapid diagnosis and treatment plan if the symptoms are indeed signaling an ischemic attack. A full stroke diagnostic workup usually includes a CT scan of the arterial blood vessels in the head and neck. Three separate tests—perfusion CT, CTA of the head, and CTA of the neck—all with contrast agent, can quickly provide the clinicians with the information needed to determine a stroke diagnosis. All 3 examinations are performed together, usually in less than 15 minutes.

Perfusion CT is used to quickly and accurately compute perfusion measurements for the assessment of cerebral ischemia. Perfusion delivers valuable information regarding the presence and extent of ischemic cerebral tissue. A cerebral ischemic event is associated with a sudden, localized reduction of cerebral blood flow. As the contrast flows through the brain, it is scanned in the same location over a given period of time. The set of images obtained represents the rate in which the tissue attenuated the contrast administrated. Perfusion shows the amount of at-risk tissue that could be saved by appropriate thrombolytic therapy. This therapy involves intravenous thrombolytic agents that rapidly break up blood clots.

Image postprocessing of the scanned area of the brain creates colormaps of the perfused tissue. Each map provides data that determine the brain's blood flow activity. Measurements of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) show how the blood reacts over time. Measurements can be calculated for a specific portion of the brain. In addition, symmetrical measurements are obtained to compare each hemisphere of the brain. In Figures 12 through 14, the perfusion images measuring CBV, CBF, and MTT demonstrate that the right hemisphere of the brain is receiving delayed or lacking blood flow in a stroke patient. Reconstructed 3D images of the middle cerebral artery (MCA) in Figure 15 correlate to the perfusion data provided in the previous images and show, in detail, the ischemic changes due to the stroke.

Figure 12Figure 13Figure 14

Figure 15

Circle of Willis imaging
The Circle of Willis, which is also referred to as the cerebral arterial circle, is a specific circle of communicating arteries located at the base of the cerebrum that receive blood from the carotid and vertebrobasilar arteries of the neck. All of the main arteries that supply blood to the brain, including the anterior cerebral artery (ACA), the middle cerebral artery (MCA), and the posterior cerebral artery (PCA), arise from the Circle of Willis.5 An interruption of blood flow through the Circle of Willis can be caused by ischemic changes, plaque, and aneurysms. This can result in stroke and substantial ensuing neurologic complications.6 In suspected cases involving the Circle of Willis, CTA of the head is performed with contrast to highlight these arterial vessels. A variety of postprocessing techniques can characterize the correct pathology when present, including MIP MPRs, CPRs, and VRTs, a series of which can give the reading clinician the views needed to provide an accurate diagnosis.

Curved planar reformats
The internal carotid arteries travel from the neck through the base of the skull. Because the skull is dense bone and the artery runs so closely to the bone, it is sometimes hard to segment the artery for a volume rendered image. CPRs allow a vessel to be manually traced through the carotid siphon to create a centerline so that the lumen can be rotated around this axis. Rotating this CPR can show disease, such as plaque, stenosis, or aneurysm. The images in Figure 16 were created with CPR of the left internal carotid artery, which is traced through the carotid siphon to the MCA. In Figure 16b, the lack of contrast has rendered the internal carotid artery to be non-visualized, due to the occlusion. In Figure 17, corresponding volume rendered view and CPR images demonstrate stenosis in both the internal and external carotid arteries.

Figure 16

Figure 17

Aneurysm diagnosis
Aneurysms are localized, blood-filled dilations of a blood vessel that are caused by a weakening of the arterial wall. Untreated aneurysms can rupture, resulting in substantial medical or neurologic complications, and are sometimes associated with sudden death. It is now thought that enzymes called matrix metalloproteinases (MMP) and other inflammatory factors may contribute to the weakening of the arterial wall.7 When an aneurysm is identified on the CT scan, different postprocessing techniques should be used to characterize the area.8 This will help the clinician decide whether the treatment should include clipping or coiling of the aneurysm. In addition, the ability to preoperatively visualize the aneurysm with 3D image reconstruction provides the surgeon with additional information that can make the aneurysm repair a safer procedure.9 Figure 18 demonstrates a variety of imaging processes that reveal the presence of an aneurysm. Figure 19, meanwhile, shows corresponding volume rendered and CPR views of an aneurysm of the left vertebral artery. The different perspectives used in Figure 19 give the clinician a better understanding of the angle at which the aneurysm dilates from the vessel.

Figure 18

Figure 19

CTA of the neck
Computed tomography angiography of the neck provides additional information on arterial vessel anatomy and pathology. The anatomy imaged with CTA of the neck includes the vessels coming off the aortic arch, including the subclavians, vertebrals, and common carotid arteries. The carotid arteries can be associated with numerous pathological findings, but atherosclerosis is a routine pathology associated with this type of imaging. Atherosclerosis is a disease in which plaque builds up in the arterial wall. This can lead to a stenosis or narrowing of the arterial wall. As the plaque builds up and stenosis progresses, the plaque may rupture, releasing small emboli that can lodge in cranial vessels, resulting in a stroke event.10 Therefore, CTA of the neck is often used to diagnose or determine the extent of atherosclerosis and to determine the patient's risk of stroke.

Determining stenosis in the internal carotids is calculated by obtaining a diameter measurement at the maximum area of stenosis and a second measurement above the stenosis in an area of normal vessels. The difference between the 2 measurements is expressed as the percent stenosis. Figure 20 provides images that demonstrate the measurements used to characterize carotid artery stenosis.

Figure 20

Adjusting for artifacts and other challenges in neck imaging
When imaging the neck, there are a variety of artifacts that can affect the quality of the scan. Patient size, dental implants, and timing of the contrast bolus are all common artifacts that influence the quality. If the quality of the scan is compromised, then the postprocessing will also be degraded. Knowing how to adjust scanning factors and protocols can improve quality in both aspects.

Figure 21

The image noise, or graininess, in Figure 21 is due to the patient's size. If the scanning dose had been increased to penetrate the more dense tissue in this patient, the quality could have been improved. If images are not postprocessed properly, the imaged vessel could incorrectly suggest disease or stenosis. In Figure 22, a 2D image of dental artifact is shown with streaking metal spray (Figure 22a). The correlating 3D image (Figure 22b) shows the interrupted vessel, gapping or missing. The quality of this scan could have been improved if the patient had removable dental work. Otherwise, the artifacts might have been minimized if the scanned field of view was reduced to exclude the hardware. Figure 22c shows the contrast in the vein as it is being injected for the scan. The bolus timing is critical when administering the contrast. Whenever possible, the contrast should be administered through the right arm. A bolus through the left arm adds to this artifact, because the contrast has to cross over the left subclavian and left common carotid before reaching the superior vena cava.

Figure 22

Cardiovascular Applications
Three-dimensional imaging has become especially important in the field of coronary medicine and cardiovascular diagnostics. Unlike traditional 2D imaging modalities, volumetric whole-organ scanning of the heart has the ability to reduce acquisition time, and single-beat, whole-heart imaging results in better images, reduced radiation exposure, reduced contrast dose, and fewer image artifacts. In addition, dual-source CT modalities are now used for heart rate-independent temporal resolution and cardiac tissue characterization.11 Multidetector CT with volumetric imaging can provide an assessment of left ventricular function, but improved temporal resolution with advanced technologies is still necessary to demonstrate comparable or superior accuracy to echocardiography or magnetic resonance imaging.12 The examples below demonstrate a few areas in which image postprocessing can provide additional diagnostic strength to existing examinations.

Cardiac CTA
Three-dimensional imaging has also become useful for performing advanced, noninvasive cardiovascular diagnostic studies. For example, as technology of CT scanners has improved, the cardiac CTA (CCTA) examination has become a reliable, noninvasive technique to evaluate the patency of coronary arteries. The coronary arteries provide blood to the heart muscle. Stenosis or complete occlusion in these arteries can result in myocardial infarction. Traditional evaluation of the coronary arteries requires the patient to undergo an invasive cardiac catheterization procedure. Meanwhile, noninvasive CCTA can evaluate stenosis and occlusion; characterize soft and hard plaques; image postoperative coronary bypass grafts; and provide assessments of functional heart wall motion. CCTA could provide an effective tool to screen patients with mild abnormalities in their initial myocardial perfusion scans to determine whether they require more expensive follow-up care with diagnostic angiography or cardiac catheterization.13

Figure 23Calcium scoring
Calcium scoring is becoming a standard tool to detect the presence of coronary artery disease (CAD) and determine an individual's risk of having a coronary event. Calcium scoring makes use of CT without contrast to determine the degree of calcification in an individual's coronary arteries, including the left main, left anterior descending (LAD), circumflex, and right coronary arteries (Figure 23). Calcium scoring provides a numerical value that indicates ranges of no calcification, minimal calcification, mild calcification, moderate calcification, or extensive calcification, depending on the degree of plaque found during the examination. The calcium scoring modality is highly sensitive for calcified lesions and the increased risk of coronary events, but cannot definitively rule out the possibility of future coronary events. For example, soft plaque is another type of lesion that cannot be seen in this non-contrast study. This type of CAD is best seen with contrast when displayed on the coronary analysis portion of the scan.

Functional heart analysis
Three-dimensional imaging is also a valuable tool to assess cardiac function. Left ventricle (LV) segmentation views can be used to determine LV performance, and 3D views can also identify cardiac long-axis and mitral valve boundaries. Wall motion can also be accurately characterized with 3D reconstruction and is used to evaluate both ventricles for prior myocardial infarcts. 3D volumetric imaging is also used to evaluate end diastolic, end systolic, and stroke volumes; ejection fraction; cardiac output; cardiac and stroke index; and myocardial mass. Stroke volume is the amount of blood ejected from the volume in each cardiac cycle. Ejection fraction is the percentage of volume that is expelled with each cardiac cycle. It is calculated as the stroke volume divided by the total volume during end diastole. Systole is when the ventricle contracts to its smallest size and ejects blood into the aorta. When the ventricle expands to its maximum size and fills with blood, the heart is in diastole.14

Functional heart analysis is a gated cardiac study that captures the cardiac cycle in each phase of the patient's heartbeat. During a heartbeat, the LV contracts to move oxygenated blood through the body. The contraction and relaxation of the LV is evaluated in the functional analysis to determine the volume of blood that is ejected with each cardiac cycle. Postprocessing of the functional analysis can provide information about the heart's stroke volume, ejection fraction, and cardiac output, as well as wall motion and wall thickness.

Figure 24The heart is situated in the chest at an oblique angle. Cardiac planes are therefore created during postprocessing reconstructions to properly assess the ventricles and atria. Once these oblique planes are aligned, the gated scan can be put into motion and the heart pumping can be visualized. The clinician would examine the myocardium for wall tissue that no longer contracts or does not contract uniformly throughout the ventricle, which may be indicative of a previous myocardial infarction. In Figure 24, the cardiac planes demonstrate each chamber in the horizontal long-axis, vertical long-axis, and short-axis view. The horizontal long-axis view, or 4-chamber view, shows both atria and ventricles. The short-axis view shows a cross section of the ventricles, and the vertical long-axis view (2-chamber view) shows the left atrium and ventricle.

The gated cardiac study provides functional information about the cardiac cycle. It captures the individual phases throughout each heartbeat. Usually, 10 phases are captured through 1 cardiac cycle, where each phase equals one-tenth of a cycle. In a gated scan, the patient's heart rate is monitored through an electrocardiogram. This allows the scanner to image each phase as the heart contracts, from peak to peak.

Figure 25Once the left ventricular volume is segmented in each phase, graphs and polar maps track the output of the calculations. In functional heart analysis, determining the amount of blood pumped out with each heartbeat is one of the most important results of postprocessing. Therefore, segmentation of the LV needs to be extremely accurate (Figure 25).

Typically, a contrast agent is given intravenously to examine both the functional analysis and the patency of the coronary arteries. The CCTA examination can be challenging when scanning because of the motion caused by the beating heart. Therefore, the gated scan factors in the patient's heart rate, and the heart rate is monitored during the study. A low, consistent heart rate is ideal for performing functional heart analysis. Technologists should be aware that a variety of factors could influence a patient's heart rate, resulting in a poor quality scan. For instance, the contrast agent can cause the heart rate to increase when administered. In addition, the bolus timing of the contrast, combined with breath holds during the scan, will also affect the heart rate. Educating and comforting the patient for what to expect during the scan can help reduce their heart rate. If necessary, β blockers can be administered in anticipation of the scan to reduce the patient's heart rate.

Coronary artery diagnostics
Three-dimensional coronary analysis with vessel probing is able to demonstrate areas of both hard and soft plaques, as well as the severity of any vessel stenosis (Figures 26 and 27). In addition, vessel probing allows the technologist to accurately identify each coronary vessel.

Figure 26

Figure 27

The coronary arteries originate from the aorta. The main arteries include the right coronary artery, left coronary artery, LAD artery, posterior descending artery, and the circumflex. These main arteries supply the blood to the heart and can be well visualized with appropriate postprocessing techniques. CPRs demonstrate the length of the vessel. These CPRs can be rotated around the centerline that was created to demonstrate a continuous lumen for each vessel. Disease and artifacts can make it difficult to track along the vessel. It is therefore important for the technologist to recognize different disease processes, anomalous arteries, stents, and grafts that may be present in these imaging studies.

Figure 28Patients with known coronary disease usually have surgery to bypass the occluded artery, often with the placement of a stent or vein bypass (graft). These stents and grafts are imaged with special attention to the proximal and distal insertion sites. Evaluation of the patency of native arteries and bypass grafts are the focus of the coronary angiography. To improve the contrast of the vessels against the heart muscle, a vessel tree of the coronary arteries can be displayed over a heart shadow (Figure 28). This technique allows the vessels to be highlighted to show anatomical landmarks and how the vessels map out over the heart (Figure 28a). This technique is particularly helpful when anomalous vessels are difficult to track, and when coronary artery bypass grafts are present (Figure 28b). These volume rendered images can also be rotated to provide the clinician with a comprehensive look at the heart.

Assessment for Abdominal Aortic Aneurysm
In assessing an abdominal aortic aneurysm, 3D imaging can be particularly useful in differentiating between the lumen, thrombus, and plaque. 3D imaging also offers clinicians additional preoperative information when planning a stent placement because the advanced imaging provides information needed for accurate stent measurement. 3D imaging is likewise used to obtain additional postoperative information after stent placement and can better characterize the patency of abdominal aortic branches.

Figure 29Endoleak classification
Endoleak classification is an especially important diagnostic tool that is assisted by 3D imaging. Endoleaks are a complication of endovascular aneurysm repair, occurring when the aneurysmal sac continues to receive arterial blood flow outside of the graft. An endoleak is evident when contrasted blood is outside the graft in the region of the aneurysm. Type II endoleaks are also possible, and are caused by retrograde flow through collateral arteries that attach to the aneurysm. The presence of a type II endoleak is characterized by high contrast blood outside the graft that can be traced to a collateral vessel (Figure 29).

Conclusions
The evolving 3D imaging modality is an important addition to medical imaging and requires dedicated, highly trained technologists who can support radiologists in image postprocessing and 3D reconstruction. 3D imaging holds particular promise in orthopedics, coronary and carotid artery imaging, imaging that assesses cardiovascular function, and assessments in patients suffering from abdominal aortic aneurysm. As the field progresses, the 3D technologists responsible for 3D image postprocessing will require advanced training so that they can be sure to receive the professional respect and credibility needed to effectively support radiologists in 3D modalities.

Acknowledgement
The author acknowledges the editorial assistance of Kristina Woodworth, a medical writer working with eRADIMAGING.com. Responsibility for the content rests with the author.

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