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14 A. R. Abadir and J. E. Silberzweig
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stiffness and torque-control characteristics. Some catheters incorporate a fine wire mesh (braid) in the wall to
increase torque transmission to the tip.
Catheters are characterized by material, shape, outer
diameter measured in French (1 mm ⫽ 3F), presence
and number of side holes, length, maximal wire diameter
accepted, and pressure rating. The most commonly used
diagnostic catheters are 4Fr and 5Fr. The size influences
the properties of the catheter, such as handling, maximal
flow rate, and size of the hole made in the artery. Diagnostic catheters (3Fr) and coaxial microcatheters (2Fr to
3Fr), designed to fit into standard sized angiographic
catheters or larger-diameter “guiding catheters,” are used
to access tortuous distal vessel branches or minimize access puncture size.
20,21
The catheter is commonly divided into three parts:
hub, shaft, and tip. The hub is on the trailing end and is
where syringes and injectors can be attached and wires
passed. The shaft provides length to the catheter to enable it to reach the target vessel. Catheter lengths are
typically 65 cm for abdominal and pelvic arteriography
and 90 to 100 cm for thoracic and carotid arteriography.
The most common site for a catheter to fail during a
power injection is at the junction of the hub and shaft
because intraluminal pressure is highest there. Fortunately, this is external to the patient. The tip of the
catheter is tapered to fit the guidewire and facilitate
atraumatic percutaneous insertion.
Shape
Perhaps the most defining element of a catheter is its
shape, as determined by the curves at its distal aspect.
Some basic, all-purpose shapes are used in almost every
case. Conversely, many catheters have been designed specifically to work for individual vessels.
High-volume, high-flow-rate studies in large vessels are
best performed with pigtail catheters. The leading end of
such a catheter is looped in a circle, and there are side
holes on the distal straight shaft to evenly disperse contrast during injection. The pigtail shape resists catheter
recoil, causing vessel injury, during high-flow contrast
injection. (Pigtail shapes also are often used for drainage
catheters because the distal circle helps prevent migration of the catheter. The side holes in drainage catheters
are larger and are in the inner aspect of the pigtail curve
to maintain patency as the drained space surrounding
the catheter collapses. Additionally, during catheter exchange over a guidewire, the guidewire is less likely to exit
a side hole located on the inner curvature of the loop.)
To catheterize a vessel selectively, the tip must be
curved or angled in such a way as to engage the origin of
the vessel of interest. Such catheters can be simple or
complex, depending on the number of curves they contain. The primary curve is the curve closest to the cathe-
ter tip. Additional curves beyond the primary curve (secondary, tertiary) help to force the catheter tip deeper
into the selected vessel once its origin has been engaged
by contacting the opposite aortic wall. Additional curves
also may help to stabilize the catheter against the aortic
wall during contrast injection.
Simple shapes have only one or two curves, such as the
hockeystick-shaped catheter (e.g., Berenstein, Kumpe).
Some arteries, such as the celiac axis or internal iliac
artery, have steeply angled origins and may be difficult to
catheterize. Two solutions to this situation are to approach these arteries superiorly (from an axillary or brachial artery puncture) or to use a catheter that has a
downward pointing tip. A downward pointing catheter
tip from a femoral approach can be achieved by either
inverting the curve of a traditional catheter on itself (e.g.,
making a Waltman loop from a braided cobra catheter)
or by using a subset of complex catheters known as recur-
vant catheters. A Waltman loop can be created by catheterizing a branch vessel of the aorta, such as the renal artery.
A guidewire then is positioned within the catheter so that
the guidewire tip is at the origin of the branch vessel.
Advancing the catheter and guidewire as a unit will form
a loop in the aorta, drawing the tip out of the branch
vessel. The tip is now directed inferiorly, ready for placement in a steeply angled vessel.
22
Recurvant catheters have a trailing curve that turns the
catheter 180 degrees back on itself, and the leading curve
(primary) serves to engage the orifice of the vessel. Examples of these are the Simmons and Sos-Selective catheters
(Fig. 2-4). The trailing curve must be reformed in a large
vessel, such as the thoracic aorta or aortic bifurcation.
Although a recurvant catheter may be used for abdomi-
FIGURE 2-4. Recurvant selective catheters. Simmons 1, Simmons 2, Simmons 3, Sos selective (
left to right
).
nal visceral catherization, the catheter shaft must be long
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enough to reach the thoracic aorta to reform its trailing
curve. The tip of the reformed catheter is brought superior to the origin of the intended vessel and drawn slowly
down until the tip engages. An interesting point to note
about looped catheters and recurvant shapes is that
catheter manipulations now have the opposite effect that
they normally do, inserting the catheter at the groin
withdraws the tip from the vessel and pulling on it advances it further into the vessel.
Recurvant catheters need to be disengaged from their
selective position before removal; other wise, the vessel
origin may be avulsed or dissected. In addition, recurvant
catheters should have their curves opened by a guidewire
before being removed from the patient.
Side holes
Catheters may have side holes in addition to the end hole
to provide a larger surface area for contrast to exit the
catheter (or for fluid to enter the catheter in the case of
drainage catheters). A higher rate of contrast injection
thus may be achieved (the taper of a catheter substantially reduces the diameter of the end hole compared
with the remainder of the catheter lumen). In addition,
a high-velocity jet, which potentially may damage the
vessel, is not formed during forceful contrast injection, as
may be the case with an end-hole catheter.
Flush catheters are designed for high-rate, high-volume injections. An example is the angiographic pigtail
catheter that has side holes placed on the straight portion
of the catheter, often several centimeters from the end,
in a “flush” configuration (Fig. 2-5). The side holes serve
to maximize the rate of contrast injection possible, center
the catheter in the vessel, and minimize unwinding of the
curved catheter tip. The number and size of holes are
constrained by the need to maintain both the strength of
the catheter and some output through the distal end.
Flush catheters typically have 8 to 12 side holes. The
lumen between the distal side hole and end of the catheter potentially can form clot if sufficient flow is not present during flushing.
Selective catheters, such as the cobra, are available as
an end hole catheter or with two small sideholes immediately adjacent to the catheter tip. The presence of the
side holes results in a diminished end hole jet during
contrast delivery with a power injector and thereby decreases the risk of intimal injury.
Situations exist, however, where the use of an end-hole
catheter is advantageous during selective catheterization.
One or two side holes projecting into the parent vessel
also may mask a situation in which the tip of the catheter
is occlusive or buried in the vessel wall by allowing blood
return. Rapid injection into such a “wedged” vessel, or
into the wall, may precipitate vessel damage or rupture.
Catheters and Guidewires 15
FIGURE 2-5. Flush catheters. Pigtail, Neff, Omni (
The pigtail and omniflush catheters have small side holes on
the distal catheter shaft to distribute the contrast and injection
force evenly (
nantly as a stabilizer and blunt leading edge. The Neff catheter
side holes (
the shaft; the operator can pull the limb down the contralateral
iliac artery for a slow selective injection rather than having to
maneuver the catheter over the aortic bifurcation.
arrows
); the tip configuration serves predomi-
curved arrows
) are on the short limb rather than on
left to right
Side hole catheters should not be used for therapeutic
embolization. The presence of a side hole increases the
risk of entangling an embolization coil at the catheter tip.
Use of side hole catheters is avoided in the coronary and
cerebral circulation because of the increased risk of
thrombus formation in the potentially stagnant blood in
the side holes or tip with subsequent embolization.
■ Conclusion
In interventional radiology procedures, planning is imperative. If the basic aspects of the case are anticipated,
unexpected situations can be handled in a rational fashion. Experience will provide a set of solutions to particular problems, but it does not substitute for a logical plan
that avoids potential problems and equipment incompatibilities. If properly performed, a percutaneous intervention can provide valuable diagnostic information and
effect a good therapeutic result with minimal risk.
REFERENCES
1. Seldinger SI. Catheter replacement of the needle in percutaneous
angiography. Acta Radiol 1953;39:368–376.
2. Schrader R, Steinbacher S, Burger W, et al. Collagen application for
sealing of arterial punctures in comparison to pressure dressings: a
randomized trial. Cathet Cardiovasc Diagn 1992;27:298–302.
3. Eisenberg RL, Fiske CE, Hedgcock MW. Catheter angiography
through aortofemoral grafts: inadvertent catheterization of the native iliac artery. AJR Am J Roentgenol 1979;32:852.
).
16 A. R. Abadir and J. E. Silberzweig
https://t.me/med1917
4. Kim D, Orron DE, Skillman JJ, et al. Role of superficial femoral
artery puncture in the development of pseudoaneurysm and arteriovenous fistula complicating percutaneous transfemoral cardiac
catheterization [Comment]. Cathet Cardiovasc Diagn 1992;126:
327–328.
5. Altin RS, Flicker S, Naidech HJ. Pseudoaneur ysm formation and
arteriovenous fistula formation after femoral artery catheterization:
association with low femoral punctures AJR Am J Roentgenol 1989;
152:629–631.
6. Sreeram S, Lumsden AB, Miller JS, et al. Retroperitoneal hematoma following femoral artery catheterization: a serious and often
fatal complication. Ann Surg 1990;4:328–333.
7. Lechner G, Jantsch H, Waneck R, et al. The relationship between
the common femoral artery, the inguinal crease, and the inguinal
ligament: a guide to accurate angiographic puncture. Cardiovasc
Intervent Radiol 1988;11:165–169.
8. Rupp SB, Vogelzang RL, Nemcek AA, Jr. et al. Relationship of the
inguinal ligament to pelvic radiographic landmarks: anatomic correlation and its role in femoral arteriography [Comment]. J Vasc
Interv Radiol 1993;4:834.
9. Spijkboer AM, Scholten FG, Mali WP, et al. Antegrade puncture of
the femoral artery: morphologic study. Radiology 1990;176:57–60.
10. Mozersky DJ, Olson RM, Coons HG, et al. Doppler controlled
needle director: a useful adjunct to angiography. Radiology 1973;
109:221–222.
11. Khangure MS, Chow KC, Christensen MA. Accurate and safe puncture of a pulseless femoral artery. Radiology 1982;144:927–928.
12. AbuRahma AF, Robinson PA, Boland JP. Safety of arteriography by
direct puncture of a vascular prosthesis. Am J Surg 1992;164:
233–236.
13. AbuRahma AF, Robinson PA, Boland JP, et al. Complications of
arteriography in a recent series of 707 cases: factors effecting outcome. Ann Vasc Surg 1993;7:122–129.
14. Grollman JH Jr, Marcus R. Transbrachial arteriography: techniques
and complications. Cardiovasc Intervent Radiol 1988;11:32–35.
15. Bakal CW, Friedland RJ, Sprayregen S, et al. Translumbar arch
aortography: a retrospective controlled study of usefulness, technique, and safety. Radiology 1991;178:225–228.
16. Yandow D, Wojtowycz M, Alter A, et al. Detection of retroperitoneal
hemorrhage after translumbar aortography by computerized tomography. Angiology 1980;31:655–659.
17. Quigley MJ, Sniderman KW, Yeung EY. Translumbar aortography:
experience with a steerable pigtail catheter. Can Assoc Radiol J
1993;44:29–34.
18. Dotter CT, Judkins MP, Fische LH. Safety guide spring for percutaneous cardiovascular catheterization. AJR Am J Roentgenol
1966;98:957–960.
19. Baum S. Catheters and injectors. In: Abrams, H, ed. Abrams’ Angiog-
raphy, 2nd ed. Boston: Little, Brown and Company; 1971.
20. Wright KC, Wallace S, Charnsangavej C, et al. Flow-directed catheter for superselective arterial catheterization: an experimental
evaluation. Cardiovasc Intervent Radiol 1986;9:54–56.
21. Reidy JF, Ludman C. The safety of outpatient arteriography using
3F catheters. Br J Radiol 1993;66:1048–1049.
22. Waltman AC, Courey WR, Athanasoulis C, et al. Technique for left
gastric artery catheterization. Radiology 1973;109:732–734.
S.I. Wahl and K. M. ZinnFilming and Injection Techniques
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3
■■■
Filming and Injection Techniques
SAMUEL I. WAHL AND KENNETH M. ZINN
Selecting the proper filming technique and injection rate
is critical in performing high-quality angiographic studies. Many variables must be considered, and each examination, or run must be tailored appropriately. The representative filming sequences and injection parameters
provided herein are those typically used at our institutions, and they may need to be modified to suit the
individual patient.
■ Image Acquisition
Currently, two basic filming techniques are used in
angiography: conventional filmscreen imaging and digital subtraction angiography (DSA) imaging. Regardless
of the techniques used, it is essential that a fluoroscopic
or scout view of the area of interest be obtained at the
start of the study, before any invasive manipulation is
done. This is especially important in the abdomen,
where retained barium from a recent computed tomography (CT) or gastrointestinal (GI) study could preclude obtaining an adequate examination. A scout film
taken immediately after placing the patient on the table
may also reveal an important element of an unknown
clinical history. For example, we saw two patients in
whom previously placed inferior vena cava filters were
discovered on scout fluoroscopy when the patients were
placed on the angiographic table for insertion of an inferior vena cava filter. In both cases, the patients were
poor “historians,” and they had incomplete medical
charts. Furthermore, it is essential that overlapping vascular segments be separated by additional views when
necessary to answer a clinical question and that multiple
views be obtained whenever critical information is
needed (Figs. 3-1 and 3-2).
Film-screen angiography
Conventional film-screen imaging is often referred to as
cut-film imaging. It has been largely replaced by digital acquisition techniques; however, it is of both historical and
current interest because it is the basis on which the subsequent technology was derived. Cut-film arteriography
uses cut sheets of film stacked or placed in a roll within a
delivery magazine or cassette called a rapid film changer.
Rapid film changers carry between 20 and 30 14 ⫻ 14inch films. They operate at maximum filming rates of
either four or six films per second (Puck, AOT-S; SiemensElema-Schonander, Inc., Elk Grove Village, IL, U.S.A.).
The number of films per second and the duration of filming during anindividual run areprogrammed into the system before each angiographic run. The most important
consideration in determining the appropriate filming sequence is the rate of blood flow in the vessel(s) being studied as well as the particular pathology being investigated,
with faster filming rates during the rapidly flowing arterial
phase and slower filming during the capillary and venous
phases. Filming near the contrast injection site generally
mandates faster rates than filming downstream at a distance from the catheter. The goal is to maximize the diagnostic information obtained during each contrast injection without excessive contrast dose or exposure to the
patient and without a waste of x-rayfilm or radiation.
Film or acquisition sequences
Filming sequences are stated as the number of films exposed per second for a specified duration of seconds. The
17
18 S. I. Wahl and K. M. Zinn
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A
B
FIGURE 3-1. Multiple views are needed to uncover overlapped vessels in this 73-year-old man with critical ischemia and a failed
left common femoral to above-knee vein-bypass graft. There is popliteal artery occlusion. The operating surgeon wishes to avoid
the groin and is planning the proximal anastomosis from the proximal superficial femoral artery. (A) An anteroposterior (AP) view
of the left femoral triangle and thigh. The arrow shows a patent proximal superficial femoral artery at the site of the proposed
proximal anastomosis. (B) The oblique view demonstrates the occluded graft stump medially and the deep femoral artery
laterally. The arrow highlights a tight stenosis at the origin of the superficial femoral artery, which was completely hidden in the
AP view. This stenosis would result in compromised inflow into a graft placed distal to it and the graft would occlude. Ultimately,
proximal anastomosis was placed at the common femoral artery as a result of this oblique angiogram.
A
FIGURE 3-2. The angiogram and physical examination must correlate. (A) An anteroposterior (AP) pelvic angiogram, part of an
aortofemoral runoff study. The patient has critical left lower-extremity ischemia, diffuse superficial femoropopliteal artery occlusive
disease, and symmetric femoral pulses. Note the extensive significant disease in the right external iliac artery. (B) Right anterior
oblique view of the left external iliac artery. The arrow highlights a significant lesion approximately 2 cm above the inguinal
ligament, which was not seen in the AP view. Because the femoral pulses were palpated as symmetric, and there is extensive
significant disease in the right external iliac artery, a hemodynamically significant lesion must be suspected somewhere in the
left common external iliac artery, and multiple obliques are mandated until the etiology of the physical finding is found.
B
Filming and Injection Techniques 19
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filming can be divided into segments, if so desired, to follow or parallel the blood flow. For example, a typical programmed run for a routine abdominal aortogram might
be three films per second for 4 seconds and then one film
per second for 8 seconds. This would expose a total of 20
films over approximately 12 seconds. In our institutions,
we would express this particular film sequence as “3 for 4
and 1 for 8.” Certain studies require that the filming continue well into the venous phase. For example, a typical
filming sequence for selective superiormesentric arteriography for GIbleeding or superior mesenteric portography
might be one film/per second for 10 seconds and then
one film every other second until the film changer has exposed the entire magazine of film (“1 for 10, then 1/2
out”). Thus, the entire run would give a total of 20 films
lasting for a total of 30 seconds, which is adequate for late
venous visualization(Table 3-1).
Filming should be tailored to the patient and the anatomy. At one extreme, rapid flow through an arteriovenous fistula mandates a minimal framing rate of
three frames per second; four to six frames per second
may be needed. On the other hand, for imaging an
aneurysm in a patient with low cardiac output, one exposure every second or every other second may suffice.
A scout film obtained prior to any contrast injection is
used to verify proposed positioning and exposure technique. Scout films usually are obtained after any significant patient repositioning as well as at the start of any
procedure.
The initial exposed film of the run is referred to as the
zero-second film. This exposure is obtained just prior to
contrast opacification. It provides a necessary baseline for
dynamic evaluation of the film run and allows the radiologist to analyze the run for any contrast-related artifacts, for example, baseline calcium projected over an
artery. Historically this film provided a “mask” for photographically subtracting out the bony background structures (after “polarizing” the film to reverse black and
white) from the images so that only the vessels being
studied are visualized. This process is called, for obvious
reasons, subtraction imaging. Since the advent of DSA,
photographic subtraction imaging is used infrequently, if
ever; however, historically it provided the conceptual basis for DSA. Zero-second and scout films also serve as a
baseline for dynamic evaluation of the run (e.g., to differentiate extravasated contrast from preexisting calcifications). This zero-second film differs from the scout film
in that the zero film is included in the total filming run.
In other words, it is the first of the sequence, whereas the
scout film is obtained prior to the actual filmed run.
TABLE 3-1. Typical Filming and Flow Rates
Study Injection Rate Filming Projections Comments
Aortic arch 40 mL total @ 20 mL/s 3/s ⫻ 4 s, 1/s ⫻ 8 s 30–45 RPO⫹ AP Pigtail ~ 1.5 cm above valve
Thoracic aorta 60 mL total @ 30 mL/s 3/s ⫻ 4 s, 1/s ⫻ 8 s 45 RPO ⫹ AP Include thoracic inlet to diaphragm
Abdominal aorta 40 mL total @ 20 mL/s or 3/s ⫻ 4 s, 1/s ⫻ 8 s AP or biplane Catheter above celiac artery
30 mL total @ 15 mL/s filming
Pelvic 30 mL total @ 15 mL/s 2/s ⫻ 3 s, 1/s ⫻ 8 s AP Oblique as needed; IPO will open iliac
Internal iliac 25–40 mL total @ 2–4 mL/s 2/2 ⫻ 3 s, 1/s ⫻ 8 s Ipsilateral PO Ipsilateral ant. oblique with penis over
Subclavian/axillary 12–20 mL total @ 3–4 mL/s 2–3/s ⫻ 4 s, 1/s ⫻ 6s AP
Brachial 12 mL total @ 3 mL/s 1–2/s ⫻ 8 s AP Check for possible high brachial bifur-
Radial/ulnar/hand 20–30 mL total @ 2–3 mL/s 1–2/s ⫻ 10–20 s Hand supinated Maximal vasodilation of extremity may
Celiac 40–50 mL total @ 5–8 mL/s 2/s ⫻ 5 s, 1/s ⫻ 10 s AP
SMA 60 mL total @ 8 mL/s 1/s ⫻ 10 s, ½ s out AP Can use 30–60/mg intraarterial papa-
IMA 15–20 mL total @ 2–3 mL/s 2/s ⫻ 5 s, 1/s ⫻ 10 s AP
Renal 12–15 mL total @ 4–8 mL/s 3/s ⫻ 3 s, 1/s ⫻ 6 s AP or 30 IAO For renal tumor evaluation, increase con-
Selective pulmonary
angiogram 40 mL total @ 20 mL/s 4/s ⫻ 4 s, 1/s ⫻ 4 s AP and 45 IPO Measure pulmonary artery pressure
IVC 60 mL total @ 30 mL/s 2/s ⫻ 3 s, 1/s ⫻ 8s AP
a
bifurcation
contralateral thigh after intracavenous
injection for impotence evaluation
cation at the axillary level; catheter
placed in axillary artery
be needed
verine to enhance venous phase; film
covers 30/s to ensure visualization of
SMV-portal vein
trast volume and delay filming for
visualization of renal vein
prior to contrast injection
AP, anteroposterior; IAO, ipsilateral anterior oblique; IMA, inferior mesenteric artery; IPO, ipsilateral posterior oblique; IVC, inferior vena cava; RPO, right posterior
oblique; SMA, superior mesenteric artery; SMV, superior mesenteric vein.
a
Flow rates and volumes are given for cut film or unsubtracted digital acquisition with full strength iodinated contrast material.
20 S. I. Wahl and K. M. Zinn
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Digital subtraction angiography
Rather than exposing cut film at regular intervals, fluoroscopically acquired images can be mapped sequentially
into computer memory. The acquisition begins with “test
shots,” which are equivalent to scouts, obtained to see
whether the angiographic unit’s programmed exposure
factors are correct. If the test shots are accepted, the
actual acquisition series begins. As with conventional
angiographic runs, a zero-second acquisition is obtained
to act as the mask by slightly delaying the contrast injection during the acquisition. From this image, some or all
the background structures can be digitally subtracted.
Precontrast background information (the “zero” exposure, or “mask”) can be subtracted out electronically
from images obtained during contrast administration.
Thus, underlying bone and soft tissue densities are subtracted out of each screen pixel (picture element) as contrast passes through the image. This markedly enhances
contrast sensitivity. Nonsubtracted images always should
be viewed along with the subtracted ones; in this manner,
underlying bone or soft tissue artifacts can be accounted
for (Fig. 3-3). Originally, intravenous injections were used
to image the arterial circulation (intravenous digital subtraction angiography, or IV-DSA), but this still required a
large amount of contrast, was subject to extensive motion
artifact, and yielded only marginal spatial resolution;
however, the use of intraarterial contrast injections (intraarterial digital subtraction arteriography, or IA-DSA)
allowed the use of smaller volumes of iodine while retain-
ing excellent contrast sensitivity; IA-DSA is also subject to
less motion artifact. Over the last decade, technical advances have markedly improved spatial resolution as
1–3
well.
Although decreased spatial resolution of DSA
compared with film-screen arteriography still exists and
can compromise the detailed evaluation of subtle smallvessel abnormalities, in clinical practice, the problem
probably occurs infrequently. Thus, IA-DSA has replaced
film-screen arteriography for most applications. The
studies also can be interpreted directly from the computer monitor, thus eliminating the wait for processing a
film run and significantly decreasing study time. Another
advantage is that the images can be electronically postprocessed to change the contrast and window level, integrate frames, and grade stenoses. Most angiographers
prefer DSA to cut-film studies because the time required
to complete the angiogram and the contrast load is significantly less than with DSA. Whereas spatial resolution
is better than with cut films with DSA, DSA has a better
chance of identifying extravasation (it is true that subtraction can be performed on cut films, but this is tedious
and expensive). We have found that DSA induces copious
artifacts when searching for a GI bleeding source (as a
result of breathing and bowel motion), and we use highresolution nonsubtracted digital acquisition in these settings with full-strength, low-osmolar contrast.
The superior contrast sensitivity of DSA allows considerable reduction in contrast density necessary to produce
optimal images. Generally, the contrast agent can be di-
A
FIGURE 3-3. Comparison of the nonsubtracted and subtracted images is extremely important when interpreting digital subtrac-
tion arteriography. (A) Selective digital subtraction arteriogram of the left external iliac artery. The single arrowhead highlights a
linear defect in more proximal external iliac artery, which might be interpreted as a guidewire-induced iatrogenic dissection. More
distal defects (dual arrows) could be similarly interpreted. (B) The nonsubtracted image demonstrates that these are really
substraction artifacts related to underlying bony cortex (arrowhead) and a hip prosthesis (dual arrows).
B
Filming and Injection Techniques 21
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luted with saline by 25 to 50%. Injection rates can be
reduced slightly compared with film-screen angiography,
but total volumes can be reduced significantly. Moreover,
one also has the option of using full-strength contrast in
a nonsubtracted mode, which may be necessary for pulmonary arteriography, abdominal arteriography, and peripheral angiography, where bowel gas, respiration, or
other patient movement causes motion artifact and pixel
misregistration.
Digital “road mapping” is a helpful utility that aids in
catheter negotiation through tortuous vessels and in
other aspects of critical catheter placement. The operator
leaves an overlay of the vasculature on the monitor from
a previous contrast injection, which can be used as a map
during the real-time fluoroscopic maneuvering of the
catheter or guidewire.
3,4
During the procedure, any fluoroscopic image can be
saved or “grabbed” for future viewing. Also, the fluoroscopic image remains on the monitor and can be magnified without requiring additional fluoroscopy. Postprocessing adjustments always can be made to improve image
quality. One new equipment option allows active rotation
of the C-arm (up to 20 to 30 degrees/second) during
contrast injection; this technique can obtain multiple
projections during a single contrast run.
With all the advantages offered by DSA, only a few
disadvantages are encountered. These stem primarily
from sequential pixel malalignment resulting from patient, cardiac, respiratory, and bowel motion. The quality
of DSA images is degraded significantly by motion, and
this problem is particularly common with abdominal and
pulmonary angiography. These problems, however, can
be reduced by giving clear patient instructions and by
using proper positioning and mild restraints. Postprocessing the acquisition by “pixel shifting” or selecting a new
subtraction mask often eliminates motion-related degradation. Glucagon and abdominal compression also can
be used before the study to decrease bowel activity. Current systems, however, allow high-quality, high-resolution
nonsubtracted digital images to be obtained in 1024 ⫻
1024 pixel matrices. Nonsubtracted digital images retain
many of the benefits of subtracted studies, including decreased table time, and can be used where motion artifact
significantly degrades the image; however, nonsubtracted
digital images require contrast rates and volumes that
approach those needed for cut-film arteriography.
The use of low osmolar contrast medium greatly reduces pulmonary irritation and therefore eliminates
coughing during pulmonary angiography. By simply using a nonsubtracted mode, excellent pulmonar y arterial
visualization is accomplished, even in the presence of
respiratory motion. With state-of-the-art digital systems,
measures used to reduce bowel and respirator y motion
are often unnecessary.
■ Aortofemoral Arteriography
Aortofemoral arteriography presents a special challenge
to filming because the target vascular territory is considerably longer than conventional film or fluoroscopic
field. The most basic approach would be to perform a
separate series over each vascular segment, working
proximally from the aorta down through the tibial and
pedal arteries. This approach would require four or five
separate film runs and contrast injections. More commonly used techniques for obtaining aortofemoral arteriograms generally employ a single programmed power
injection and either table or image intensifier movement
or special long film cassettes to acquire images in a single
series. The more commonly used devices for aortofemoral arteriography are the stepping table and “bolus chasing.” The long-leg changer (BC Medical Ltd.,
Montreal, Quebec, Canada), another such device, is no
longer manufactured, but it is still in use.
A stepping table traditionally used a rapid film changer
(Puck or AOT-S film changer 14 ⫻ 17-inch film) as the
patient is moved in “steps” over several different stations,
extending from the pelvis to the feet during a single
contrast injection. A long-leg changer, on the other hand,
is a ceiling-mounted x-ray tube that uses multiple (usually
six) 14 ⫻ 51-inch film cassettes housed within a rotating
film unit below the patient. The time interval between
each cassette exposure can be tailored to the patient so
as to ensure complete opacification from the distal aorta
to the pedal vessels. Such large-field changers are advantageous for arteriography and venography of the lower
extremities because the entire extremity can be evaluated
on each exposure, and calculation of the timing for lower
extremity arteriography is less crucial. The disadvantages
are the need for an additional ceiling-mounted radiographic tube with a tube to a floor distance of between 87
and 110 inches and a maximum filming rate of one film
every 2.5 to 3 seconds. Extremely long contrast columns
(8 to 10 seconds) are imaged. Late-generation stepping
tables can acquire images digitally.
Finally, new digital “bolus chasing” techniques are an
alternative to both a traditional stepping table or a longleg changer. With bolus chasing, the operator can control table movement manually while visualizing contrast
opacification in real time. The operator then can alter
the rate of the table movement to match the speed and
position of the contrast bolus (i.e., bolus chasing), acquiring images longitudinally. Digital subtraction is accomplished by duplicating the table movement and
frame rate after the contrast has dissipated to obtain a
“mask.” “Knee-arrival time” is computed by fluoroscopically observing a small test bolus of contrast arrive at the
popliteal artery prior to the full injection; then it is used
by the system’s microprocessor to optimize the contrast
22 S. I. Wahl and K. M. Zinn
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injection rate and volume and to coordinate it with an
appropriate acquisition sequence.
Opacification of extremities can be enhanced, if necessary, by inducing reactive hyperemia after the release of
pressure cuffs from the calves, warming the extremity, or
using vasodilators such as intraarterial nitroglycerin, tolazoline, or papaverine. Of these, transcatheter nitroglycerin, 200 lg, is preferred by some for augmenting visualization of the lower extremities.
1
Spot films using 70-mm or 105-mm cameras are sometimes used in angiography, but the small size of the
frames makes fine detail difficult to appreciate, and these
are now considered “legacy” devices by many. Cineradiography is found primarily in cardiac angiography suites,
but the high radiation doses and the cumbersome smallfield film viewing make it insufficient for abdominal and
extremity work. Most peripheral arteriograms do not require the extremely rapid frame rate necessary in cardiac
angiography.
■ Flow Rates and Contrast Injectors
As stated previously, selecting the proper contrast flow
rate for angiography is an extremely important part of a
high-quality angiogram. Several programmable automated injection devices are commercially available that
provide predictable and reproducible contrast volumes
delivered at a specific flow rate for angiographic studies.
For example, a routine (digital) abdominal aortogram
may require a total contrast volume of 30 mL at a flow
rate of 15 mL/second (i.e., a 2-second injection).
Power injectors must be programmed prior to each
run, depending on the vascular territory being studied,
avoiding the inconsistent, unknown rates of hand injections. Furthermore, power injectors can deliver higher
flow rates than hand injections. It is imperative that, prior
to a power-injected run, a hand-delivered test injection be
performed to ensure proper catheter position and to
confirm the flow rate required.
The primary injection parameters programmed into
the power injector prior to the run are the flow rate
(mL/sec), the total contrast injection volume (mL), and
the linear rise (Fig. 3-4). The flow rate is selected on the
basis of vessel diameter and blood flow observed fluoroscopically with a hand injection. Total contrast volume
depends on the desired column length and the size of the
territory to be opacified. For example, a 1.5- to 2-second
contrast column issufficient to fill thefield of a thoracic or
abdominal aortogram. Image acquisition must be delayed
so that at least one noncontrast zero-second image is acquired for a maskbefore the arrival ofcontrast in the field.
When the area of interest is at the catheter injection site,
the injection typically is delayed 0.5 to 1 second after the
start of image acquisition. If imaging is remote from the
site of injection, however, a variable delay in filming may
be programmed to occur after the start of the contrast
injection. For example, with a catheter injection in the
common iliac artery and filming over the foot, a long
filming delay (e.g., 7 to 10 seconds) can aid in extending
the series to allow acquisition of a good foot arteriogram.
A catheter-specific maximum pressure limit is set to avoid
catheter rupture during power injection. (Note that pressure is not a primary parameter.) Pressure generated during injection is related to the viscosity of the contrast medium, the programmed flow rate, the catheter luminal
diameter, and catheter material and length. For example,
a typical nylon, 90-cm, 5F pigtail catheter might have a
A
FIGURE 3-4. The injection settings for a flush aortogram are shown on the control panel from a Mark V power injector (Medrad,
Inc., Pittsburgh, PA, U.S.A.). (A) The pressure limit is set 999 pounds per square inch (psi) just below the catheter pressure limit.
(B) By using the “status function” button, the interventionalist can view the actual injection parameters after the run is completed.
The arrow demonstrates that the combination of flow parameters, contrast viscosity, and catheter factors actually generated a
pressure of 760, considerably less than the set pressure limit.
B
Filming and Injection Techniques 23
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maximum pressure limit of 1050 pounds per square inch
(psi). Excess pressure generally causes rupture at the
catheter hub, where pressure ishighest. Atthe setpressure
limit, a power injectortypically willterminate the injection
so that rupture is avoided (Fig. 3-4).
Linear rise is an additional primary injection parameter. It is the time required from the onset of the injection
(zero flow) to reach the maximum flow rate specified by
the injector. Linear rise is used to avoid catheter recoil
and should depend on the catheter type and position. A
typical linear rise of 0.2 seconds is usually sufficient for
multi-sidehole catheters during flush aortography. A
longer linear rise (0.4 to 0.8 seconds) decreases the likelihood of catheter recoil (and selective vessel damage)
and should be used during selective arteriography.* For
example, if an end-hole catheter is selectively placed in a
vessel, the sudden recoil produced by the maximum rate
of injection without a gradual rise potentially could dislodge the catheter or, worse, damage the vessel. Nonselective flush catheters with sideholes may allow the use of
a shorter linear rise (0.2 seconds) as the contrast is generally distributed equally in all directions from the multiple holes maintaining the catheter’s position. Generally,
selective catheters with sideholes should be used with
medium to long linear rise times. Contrast injectors also
usually include a contrast syringe heater to reduce contrast viscosity and to allow flow rates of up to 40 mL/sec.
The 4 to 5 Fr catheters commonly used today are subject
to considerably more recoil for a given flow rate than the
6 to 7 French catheters that were common a few years
ago; thus, we have tended to use longer linear rise times
when in selective positions.
■ Contrast Agents
Our central tenet is to administer the minimal amount of
contrast necessary to obtain complete diagnostic information or complete an interventional study. Increasing
volumes may add additional risk to patients with poor
cardiac output or renal failure. Low-osmolality contrast
agents are preferred in most vascular and interventional
radiology departments because they decrease patient discomfort and reduce the incidence of adverse side effects,
such as contrast-induced renal failure compared with
conventional, higher osmolar agents. They also appear to
reduce minor contrast reactions, such as urticaria, nau-
* This concept can be explained easily compared with sitting
idle at a traffic light. When the light turns green, and you
abruptly push your foot against the accelerator, a considerable
amount of recoil will be placed on your head forcing it backwards; if you gradually depress the accelerator in a progressive
linear fashion, however, much less recoil will be encountered.
sea, and vomiting. Although rare, severe and fatal reactions are not eliminated by using low-osmolar contrast
agents. The efficacy of steroid prophylaxis with low osmolar contrast is controversial. Institution-specific protocols
should be consulted and followed.
6–8
The occurrence of clinically significant contrast-related renal dysfunction usually is associated with preexisting renal compromise. Advanced age and diabetes contribute to risk.
9
Patients with multiple myeloma may incur
renal damage as a result of tubular precipitation in highrisk groups; so imaging examinations that do not require
iodinated contrast material should be considered if they
can give clinically useful data. It is essential that patients
who are high risk for renal failure receive low osmolar
contrast. Some angiographers use furosemide and mannitol infusions to maintain renal blood flow and prevent
renal toxicity, but benefit from this protocol remains controversial.
10–13
Full-strength iodinated contrast for angiography generally ranges from 300 to 370 mg/mL iodine. Dilute
contrast for injection may be half to two-thirds strength
when using digital acquisition. The newer contrast agents
do not have anticoagulant properties typical of standard
high-osmolar contrast; thus, it is essential that low-osmolar agents not be allowed to contact blood for long periods. Thus, care must be taken not to allow blood to dwell
5
in power-injector syringes, tubing, or catheters prior to
injection.
Despite the low incidence of contrast reactions using
low-osmolar, iodinated contrast agents, the potential for
problems in patients with a history of prior allergic reactions and in those with renal insufficiency remains. For
this reason, carbon dioxide (CO
viable alternative contrast agent.
) was developed as a
2
14
Carbon dioxide is a nonallergic, highly dissolvable gas
that is excreted by the lungs, avoiding the nephrotoxicity
of iodinated agents. By temporarily displacing blood,
CO
decreases the radiographic density within the vessel
2
lumen, essentially the opposite radiographic effect of traditional contrast agents. CO
can be used as an intravas-
2
cular contrast agent for both diagnostic and interventional studies; however, because of its potential for
neurotoxicity, it is not used for studies performed above
the diaphragm. Special delivery techniques have been
designed for CO
with air can be fatal.
because it is colorless, and admixture
2
15
One must be careful to use small,
controlled injection volumes and correct patient positioning to avoid gas trapping in nondependent structures
such as the main pulmonary artery. The trapped gas can
obstruct pulmonary blood flow, leading to cardiac failure. If the injection volume, duration, and interval are
adequate, unlimited quantities of CO
can be used. CO
2
angiography has been used during TIPS (transjugular
intrahepator portosystemic shunt) procedures with excellent results; however, its contrast resolution is inferior to
2
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