Introduction to Fluoroscopic Techniques: Anatomy, Setup, and Procedural Pearls




Abstract


This chapter describes basic and advanced fluoroscopy techniques to achieve optimal C-arm setups. These include an understanding of the C-arm operation, fluoroscopic anatomy, basic projections, optimal views, and parallax.


The first step to a successful procedure includes setting up the C-arm according to the anatomy of the specific targeted segment. The C-arm setup determines the trajectory that the needle will take to reach its target, provided that the operator uses “down the beam” technique. It should be evident that a safe, efficient, and effective procedure is dependent on an optimal C-arm setup.


The authors would like to emphasize that the setup should be specifically focused on the target segment. Visual recognition of bony landmarks, rather than specific measurements or angles, is emphasized, given that the morphology and orientation of each anatomic segment can differ.


The challenge for an interventionalist is to reconcile the two-dimensional configuration of the fluoroscopic image with the three-dimensional anatomy of the patient. Such an understanding requires time, practice, and knowledge of spinal anatomy and fluoroscopy.


In the latter half of the chapter, these more “advanced” fluoroscopic techniques will help the reader obtain the skills needed to troubleshoot any nonoptimal image, and therefore provide the safest and most efficient procedure for the patient.


The following fluoroscopic techniques will help to optimize the visualization of key bony landmarks when positioning the needle to reach a specific target.




Keywords

Fluoroscopy, Injection, Pain Management, Pearls, Positioning, Radiculopathy, Spine

 



Note: Please see pages ii , iii for a list of anatomic terms/abbreviations used throughout this book.


This chapter describes basic and advanced fluoroscopy techniques to achieve optimal C-arm setups. These include an understanding of the C-arm operation, fluoroscopic anatomy, basic projections, optimal views, and parallax.


The first step to a successful procedure includes setting up the C-arm according to the anatomy of the specific targeted segment. The C-arm setup determines the trajectory that the needle will take to reach its target, provided that the operator uses “down the beam” technique. It should be evident that a safe, efficient, and effective procedure is dependent on an optimal C-arm setup.


The authors would like to emphasize that the setup should be specifically focused on the target segment. Visual recognition of bony landmarks, rather than specific measurements or angles, is emphasized, given that the morphology and orientation of each anatomic segment can differ.


The challenge for an interventionalist is to reconcile the two-dimensional configuration of the fluoroscopic image with the three-dimensional anatomy of the patient. Such an understanding requires time, practice, and knowledge of spinal anatomy and fluoroscopy.


In the latter half of the chapter, these more “advanced” fluoroscopic techniques will help the reader obtain the skills needed to troubleshoot any nonoptimal image, and therefore provide the safest and most efficient procedure for the patient.


The following fluoroscopic techniques will help to optimize the visualization of key bony landmarks when positioning the needle to reach a specific target.




Review of Spine Anatomy ( Fig. 3.1 )





Fig. 3.1


A, Model of a spine in the lateral position, with needles at different angles demonstrating the natural curvature (i.e., lordosis or kyphosis) of the spine. Note the different C-arm tilt angles for the needle trajectories at each spinal segment. B, Lateral radiograph of a spine demonstrating cervical lordosis (not well visualized on the far left of image), thoracic kyphosis, and lumbar lordosis. Compare with Fig. 3.1A to anticipate needle trajectories for each spinal segment.




C-Arm Equipment ( Figs. 3.2 and 3.3 )





Fig. 3.2


A, Cone-shaped fluoroscopic beam coming from the smaller diameter image source to the larger diameter image intensifier. The nomenclature used throughout this atlas is based on the movements of the larger diameter image intensifier and not the beam or image source. B, Monitors with lateral image and patient information. C, Foot pedal. D, Control panel on the fluoroscope base unit. E, Control panel on the monitor.




C-Arm Movements and Nomenclature ( Fig. 3.3 and Table 3.1 )




Table 3.1

Definitions of the Different C-Arm Movements and the Nomenclature Used Throughout This Atlas ∗







































Movement Figure/Photograph/Diagram of Movement Description Nomenclature Used in This Atlas
Cephalad or caudad tilt (also known as decline) Fig. 3.3A and B The C-arm rotates around a transverse axis with the image intensifier (ImInt) rotating superiorly while the X-ray source rotates inferiorly (or vice versa).
If the patient is side-lying, this will create a similar motion relative to the patient as wig-wag in patients in the supine or prone position ( Table 3.3 ). 		0-degree tilt: straight up and down (perpendicular to the patient). The ImInt toward the head is cephalad tilt and toward the feet is caudad tilt.
Oblique Fig. 3.3C, D, and E The C-arm rotates circumferentially (ImInt right or left) and moves around the patient either toward or away from the interventionalist. 0 degrees: anteroposterior (straight up and down).
90 degrees: lateral.
The ImInt toward the right is right oblique.The ImInt toward the left is left oblique.
The C-arm toward the needle tip is ipsilateral oblique and away from the needle tip is contralateral oblique (CLO).
Piston (also known as in/out translation, left/right translation, or telescope) Fig. 3.3F The C-arm translates toward the patient’s right or left. Fig. 3.3F depicts this in the anteroposterior (AP) view (0-degree oblique). Pistoning can also be done with the C-arm in other oblique angles, including the lateral view (90-degree oblique). When in the lateral position, the ImInt movement toward or away from the patient can make the image less or more magnified, respectively. The C-arm is to the patient’s right or left.
Head/foot translation The entire C-arm moves parallel to the patient, either superiorly toward the head or inferiorly toward the feet. The direction of C-arm translation is dependent on which way the wheels are facing. Most machines can be locked to only translate in one plane at a time. The C-arm translation is cephalad or caudad.
Up and down (ceiling/floor elevation) The C-arm moves toward the ceiling or the floor. The ImInt moves toward or away from the patient, thus making the image less or more magnified, respectively. The C-arm is up toward the ceiling or down toward the floor.
Wig-wag (swivel) Fig. 3.3G The wig-wag technique involves the use of a third plane of axis. It is typically used while the C-arm is in a lateral position (i.e., 90-degree oblique), with the C-arm’s ImInt rotating inferiorly while the source rotates superiorly (or vice versa). The typical goal of this technique is to position the X-ray beam perpendicular to the imaged target structure and/or needle. This motion is also used to separate overlapping structures or needles.
Because the rotation axis is actually around the C-arm base (and not the patient), the C-arm typically will need to be translated back to the treated segment after the wig-wag movement.
If the patient is side-lying, this will create a similar motion relative to the patient as tilting in the supine or prone position ( Table 3.3 ). 		The C-arm wig-wag rotation is around the patient either clockwise or counterclockwise.

∗ The terminology is based on the image intensifier (ImInt, and not the image source) movements.










Fig. 3.3


A, Cephalad tilt of the fluoroscope. B, Caudad tilt of the fluoroscope. C, 0-degree oblique. D, 45-degree right oblique. E, 90-degree oblique (lateral). F, Pistoning of the fluoroscope. The left arrow indicates pistoning toward the interventionalist, and the right arrow indicates pistoning away from the interventionalist. G, Wig-wag of the fluoroscope demonstrating both 0 degrees and approximately 20 degrees of clockwise wig-wag relative to the patient.




Identifying Spinal Segments/Confirming the Levels ( Figs. 3.4 to 3.8 )


Cervical


For a patient with normal spinal segmentation, identify the level by counting cephalad from the cervicothoracic junction in the anteroposterior (AP) view or down from the C2/axis (with the odontoid process/dens) in the lateral or AP projection. For procedures that will be performed in the oblique projection (i.e., cervical transforaminal), identify the level by locating the most superior intervertebral foramen, which is the C2-C3 foramen where the C3 spinal nerve exits, and then count caudad. The C7 and T1 segments are transitional vertebrae and thus have intermediate features in relation to the cervical and thoracic spine. The C7 transverse process (TP) is longer than its cervical counterparts but shorter than the T1 TP. It appears slightly downsloping and has a configuration that can be likened to that of a “short, stubby thumb.” The T1 TP is longer than the C7 TP, broader than the thoracic TPs, and slopes upwards superolaterally ( Fig. 3.4 ).




Fig. 3.4


A, Fluoroscopic lateral view of the cervical spine with C2 (axis) labeled. Note that the spinous process of C2 is bifid. B, Fluoroscopic anteroposterior (AP) view of the cervical spine with C2 labeled. C, Fluoroscopic foraminal oblique view of the cervical spine with the C2-3 foramen; where the C3 spinal nerve exits is labeled. Note that the most superior neural foramen of the cervical spine is C2-3 (labeled “C3”). A spinal needle approaches the C6-7 neural foramen, where the C7 spinal nerve exits. D, Fluoroscopic AP view of the cervicothoracic spine with C7 and T1 labeled. Note that the C7 transverse process (TP) is longer than its cervical counterparts but shorter than the T1 TP and appears slightly downsloping. The T1 TP is longer than the C7 TP, broader than the thoracic TPs, and slopes upwards superolaterally.



Fig. 3.5


A, Fluoroscopic anteroposterior (AP) view of the thoracolumbar spine with T12 labeled. B, Fluoroscopic AP view of the lumbosacral spine with L5 labeled.



Fig. 3.6


A, This patient had a suspected “T12-L1” discitis identified on T2-weighted magnetic resonance imaging (MRI). The “T12-L1” level (arrow) was identified on the basis of counting up, superiorly, from the lumbosacral junction. B, AP plain film with the same “T12-L1” level identified (arrow) by counting up from the lumbosacral junction. Note its location relative to the thoracolumbar juction; C, intraprocedural fluoroscopic lateral; and D, intraprocedural fluoroscopic AP of the “T12-L1” disc biopsy. When we performed the fluoroscopically guided biopsy, we correlated the fluoro and plain film images with the MR images by also counting up from the sacrum and confirming the narrowest disc as seen on MRI, plain film, and fluoroscopic imaging. Note that we would have potentially chosen the wrong level had we only counted down from the most inferior rib on intraprocedural fluoroscopic AP.



Fig. 3.7


T2-weighted scout localizer magnetic resonance imaging (MRI) that includes C2 for definitively determining proper segmental enumeration. “Markers” are placed on the dorsal skin prior to the MRI scan. A, Cervicothoracic segments. Note the C2 vertebral segment (closed arrow) . A marker is demonstrated over the skin dorsal to the superior aspect of T11 (open arrow) . B, Thoracolumbar segments. The same marker is used to assist in counting down to the lumbosacral junction for definitive enumeration.



Fig. 3.8


A, T2-weighted sagittal magnetic resonance (MR) image of a patient with a transitional segment ( lumbarized S1 ). In this case, the yellow arrow indicates the pathology of interest, an L5-S1 disc protrusion encroaching the traversing S1 nerve root. This patient has radicular pain in the S1 distribution and is to receive an S1 (S1-2) transforaminal epidural steroid injection. B, Fluoroscopic lateral view of the same patient with a lumbarized S1 transitional segment. The needle is in the S1 (S1-2) foramina, and the yellow arrow indicates the L5-S1 disc space. Note that the S1 (S1-2) foramen, because it is lumbarized, resembles that of the typical lumbar segments. The intent was to place medication along S1, with the contrast and medication directed superiorly toward the posterior L5-S1 disc. Without correlating MR and fluoroscopic images, an inexperienced interventionalist may have mistaken the segments and may not have addressed the intended level. C, Fluoroscopic anteroposterior (AP) view with the same needle approaching the S1 (S1-2) foramen. The lumbarized S1 transitional segment is labeled. D, Fluoroscopic AP view showing the flow of contrast outlining the S1 nerve root and exiting the spinal nerve.


Thoracic


For a patient with normal spinal segmentation, identify the level in the AP view by counting caudad from the cervicothoracic junction ( Fig. 3.4D ) or cephalad from T12 ( Fig. 3.5 ). The ribs can be used as a segmental counting guide, but caution must be taken. Some patients may have a cervical (extra) rib or may lack obvious T12 ribs, and therefore do not have 12 reliably distinct ribs for landmarks. Caution must be used when correlating the lowest thoracic rib to lumbar magnetic resonance imaging (MRI) findings because they are typically interpreted/enumerated on the basis of the lumbosacral junction (see Figs. 3.5 through 3.7 ).


Lumbosacral


For a patient with normal spinal segmentation, identify the level in the AP view by counting caudad from T12 ( Fig. 3.5A ) or cephalad from the lumbosacral junction ( Fig. 3.5B ). As stated above, the ribs can be used as a segmental counting guide, but caution must be taken. Some patients do not have 12 reliably distinct ribs for landmarks. Even when a distinct 12th rib is identified, atypical enumeration can occur ( Fig. 3.6 ), as described in the next section.


Lumbosacral Transitional Segments/Atypical Segmental Enumeration


In up to 15% of the population, a transitional segment may occur. Transitional segments are typically described as involving the lumbarization of the first sacral segment or the sacralization of the fifth lumbar segment. Rarely patients will have six lumbar vertebrae, and some consider these to be lumbarized S1 segments because an L6 spinal nerve is typically not described. In fact, studies suggest that L6 segments do indeed behave like S1 segments; in patients with only four lumbar vertebrae, the inferiormost lumbar segment L4 behaves like L5. Extra or missing ribs may add to the counting confusion ( Fig. 3.6 ). Similarly, as discussed above, some patients may have an aberrant segmentation of the cervicothoracic junction, thoracolumbar junction, or both. Therefore, if a transitional segment is suspected, an MRI scout image is recommended for the purpose of counting caudad from C2 to the lumbosacral junction. If a lumbosacral transitional segment is suspected, coronal T2 images should be specifically requested and/or the scout including C2 ( Fig. 3.7 ) because they may not be routinely included with a lumbar MRI.


Ultimately, it is most important to correlate the patient’s clinical symptoms with the pathoanatomy visualized on the available imaging. Subsequently, fluoroscopic images obtained during the procedure need to be correlated with the same visualized pathoanatomy. The demonstrated example ( Fig. 3.8 ) is of a patient who has right L5 and/or S1 symptoms with MRI suggesting lumbarization of S1 and an extrusion at L5-S1 (yellow arrow). The intent was to administer medication along S1, with the contrast and medication directed superiorly toward the posterior L5-S1 disc.


We strongly encourage correlating the plain X-ray lateral and fluoroscopic lateral image with the midline sagittal MR image so that the proper levels are chosen. We cannot overemphasize the importance of documenting and communicating the transitional segmental convention used with other treating physicians and/or providers.


We suggest reviewing available plain films and MRI correlation preprocedure to avoid unnecessary radiation that occurs with doing this with live fluoroscopy. Often, practitioners will unnecessarily focus on the lumbar numbering (i.e., counting caudad from T12 and/or counting cephalad from the sacrum) instead of our recommendation of simply correlating the available imaging (i.e., the sagittal MRI and the lateral plain and fluoroscopic imaging). It is imperative that the presence of the transitional segment is well communicated and documented so that all treating physicians/practitioners use the same enumeration terminology.


Confirming the Correct Segment: A Technical Note


If the interventionalist remains uncertain as to which segment to target after preprocedural review of imaging studies, a much smaller “marker needle” (e.g., a 25- or 27-G, 1.5-inch needle) can be placed in the AP view at the segment that is believed to be the correct segment before switching to a lateral view to confirm that the correct segment has been identified. In doing so, the interventionalist can minimize trauma to the patient if the targeted segment turns out to be incorrect or advantageously anesthetize a soft tissue track for the injection should the targeted segment turn out to be the correct segment.




Obtaining “True” Anteroposterior Views


“Treat the Patient, Not the Table”


Each segment is not necessarily aligned with the others as a result of normal anatomy (e.g., lordosis, kyphosis, etc.), pathology (e.g., lateral or rotary scoliosis, listhesis, etc.), positioning on the table, or some combination of these factors. To optimize the efficiency and safety of a procedure, the proper positioning of the C-arm to obtain a “true” AP view of the targeted segment is recommended. Note that if an oblique adjustment of the C-arm is required to obtain a “true” AP view, geometry dictates that a similar adjustment will be required to obtain a “true” lateral view (see Obtaining “True” Lateral Views, below).


Oblique the C-Arm to Optimize the “True” Anteroposterior View


The C-arm image intensifier is obliqued to obtain a “true” AP view relative to the specific segment being targeted, with the spinous process (SP) at the midline of the vertebral body and equidistant from each pedicle. Also note that in the “true” AP view, the left and right cortical borders of the SP should appear equally dense. The “true” AP view is not necessarily at 0 degrees of obliquity, as indicated on the fluoroscope. If the patient has multiple levels to be treated, a “true” AP should ideally be obtained at each segment being targeted ( Fig. 3.9 ).




Fig. 3.9


A, Fluoroscopic anteroposterior (AP) view of the cervicothoracic spine with the T1 segment labeled and a needle tip at the inferior aspect of the C7 lamina. Notice the spinous process of T1 is not centered; therefore, T1 is not at “true” AP. B, By obliquing the C-arm leftward, toward the T1 spinous process, it is now centered (and the left and right cortical borders of the spinous process became equally dense) and is at “true” AP. Notice that this also affects C7 to a certain degree as its spinous process is now approaching the midline, but C7 is still not at “true” AP. This is because the vertebral segments are independent of one another and must be individually addressed. C, Fluoroscopic AP image of the L-spine with the needle tip at the L5 lamina. Note the spinous process of L5 is not centered (and the left cortical border of the spinous process is more dense than the right); therefore, L5 is not at “true” AP. D, By obliquing the C-arm leftward toward the L5 spinous process, it is now centered (and the left and right cortical borders of the spinous process are equally dense) and is at “true” AP. The needle, in this case, had since been withdrawn.


Tilt the C-Arm to Optimize the “True” Anteroposterior View


The vertebral body end plates, which are circumferentially bordered by the ring apophysis, cover both the superior and inferior horizontal surfaces of the vertebral body. Lining up the vertebral body end plates is an important skill for obtaining a clear and direct view of the target region for many procedures. For example, when performing discography, the trajectory view requires direct parallel visualization of the end plates. This fluoroscopic view is obtained with the cephalad or caudad tilt of the C-arm image intensifier. In this example, this optimizes the superior end plate of the inferior vertebral body, which is visualized as a solid horizontal line rather than as an ellipse ( Fig. 3.10 ).




Fig. 3.10


A, Anteroposterior (AP) image of the L-spine with the superior end plate of L5 preferentially lined up. Note the more elliptical shape of the inferior end plate of L5 because the superior and inferior end plates of the vertebral bodies are usually not anatomically parallel to each other. The L4 end plates are clearly not lined up and also appear elliptical. B, An AP image of the same patient with the C-arm tilted to line up the superior end plate of L4. Note the more elliptical shape of the inferior end plate of L4 because the superior and inferior end plates of the vertebral bodies are usually not anatomically parallel to each other. The L5 end plates are now clearly not lined up because they appear elliptical. C, A lateral image of the same patient with the yellow line representing the projection of the beam through the superior end plate of L5 (corresponding to Fig. 3.10A ) and the red line representing the projection of the beam through the superior end plate of L4 (corresponding to Fig. 3.10B ). Note that tilting the C-arm is necessary to line up the superior end plate of L4 versus L5.




Obtaining “True” Lateral Views


As noted above, each segment is not necessarily aligned with the others as a result of the normal anatomy (e.g., lordosis and kyphosis), pathology (e.g., lateral or rotary scoliosis, and listhesis), positioning on the table, or some combination of these factors. To optimize the efficiency and safety of a procedure, the C-arm’s oblique and wig-wag (swivel) features should be used to obtain a “true” lateral view of the targeted segment.


Oblique the C-Arm to Optimize the “True” Lateral View


The C-arm should be obliqued 90 degrees from the angle at which the “true” AP view was obtained. The table may need to be laterally rotated to accommodate angles that cannot be obtained with the C-arm obliquely. When patients have multiple levels to be treated, the “true” lateral view should be ideally obtained for each respective level.


For the cervical spine, a “true” lateral view may be obtained by lining up the lateral masses. If the patient is prone or supine, this is accomplished with the use of the wig-wag feature and may require additional obliquing of the C-arm or table. If the patient is in a side-lying position, this is accomplished by tilting and occasional obliquing. Sometimes each segment must be lined up individually ( Fig. 3.11 ; see also Chapter 4 for further discussion).


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Jan 27, 2019 | Posted by in RHEUMATOLOGY | Comments Off on Introduction to Fluoroscopic Techniques: Anatomy, Setup, and Procedural Pearls

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