A Review of the Benefits and Pitfalls of Phantoms in Ultrasound-Guided Regional Anesthesia

Article (PDF Available)inRegional anesthesia and pain medicine 36(2):162-70 · March 2011with387 Reads
DOI: 10.1097/AAP.0b013e31820d4207 · Source: PubMed
Abstract
With the growth of ultrasound-guided regional anesthesia, so has the requirement for training tools to practice needle guidance skills and evaluate echogenic needles. Ethically, skills in ultrasound-guided needle placement should be gained in a phantom before performance of nerve blocks on patients in clinical practice. However, phantom technology is varied, and critical evaluation of the images is needed to understand their application to clinical use. Needle visibility depends on the echogenicity of the needle relative to the echogenicity of the tissue adjacent the needle. We demonstrate this point using images of echogenic and nonechogenic needles in 5 different phantoms at both shallow angles (20 degrees) and steep angles (45 degrees). The echogenicity of phantoms varies enormously, and this impacts on how needles are visualized. Water is anechoic, making all needles highly visible, but does not fix the needle to allow practice placement. Gelatin phantoms and Blue Phantoms provide tactile feedback but have very low background echogenicity, which greatly exaggerates needle visibility. This makes skill acquisition easier but can lead to false confidence in regard to clinical ability. Fresh-frozen cadavers retain much of the textural feel of live human tissue and are nearly as echogenic. Similar to clinical practice, this makes needles inserted at steep angles practically invisible, unless they are highly echogenic. This review describes the uses and pitfalls of phantoms that have been described or commercially produced.
A Review of the Benefits and Pitfalls of Phantoms
in Ultrasound-Guided Regional Anesthesia
Graham Hocking, MBChB, DMCC, FRCA, FANZCA, FFPMANZCA,*Þ
Simon Hebard, MBChB, BSc, MRCP, FRCA,Þ and Christopher H. Mitchell, MBBS, FANZCAÞ
Abstract: With the growth of ultrasound-guided regional anesthesia, so
has the requirement for training tools to practice needle guidance skills
and evaluate echogenic needles. Ethically, skills in ultrasound-guided
needle placement should be gained in a phantom before performance
of nerve blocks on patients in clinical practice. However, phantom
technology is varied, and critical evaluation of the images is needed to
understand their application to clinical use. Needle visibility depends on
the echogenicity of the needle relative to the echogenicity of the tissue
adjacent the needle. We demonstrate this point using images of echo-
genic and nonechogenic needles in 5 different phantoms at both shallow
angles (20 degrees) and steep angles (45 degrees). The echogenicity
of phantoms varies enormously, and this impacts on how needles are
visualized. Water is anechoic, making all needles highly visible, but
does not fix the needle to allow practice placement. Gelatin phantoms
and Blue Phantoms provide tactile feedback but have very low back-
ground echogenicity, which greatly exaggerates needle visibility. This
makes skill acquisition easier but can lead to false confidence in regard to
clinical ability. Fresh-frozen cadavers retain much of the textural feel of
live human tissue and are nearly as echogenic. Similar to clinical prac-
tice, this makes needles inserted at steep angles practically invisible,
unless they are highly echogenic. This review describes the uses and
pitfalls of phantoms that have been described or commercially produced.
(Reg Anesth Pain Med 2011;36: 162Y170)
Phantom
noun. 1. Something apparently seen, heard, or sensed,
but having no physical reality; a ghost or apparition;
something elusive or delusive. 2. An image that appears
only in the mind; an illusion.
adj. merely ap par ent, illusory, imaginary, false, fake;
devised to imitate or deceive.
(Definitions from the Oxford English Dictionary and Wiktionary)
W
ith the rapidly increasing use of ultrasound in regional
anesthesia, we have to consider how best to teach safe
ultrasound-guided needle placement. There is an emerging
consensus that it is no longer acceptable to use patients to gain
this early experience.
1Y9
The use of phantoms in ultrasound-
guided regional anesthesia (UGRA) can facilitate this process.
For the purposes of this review, a phantom is any media other
than live human tissue that can be used for research or training.
Phantoms provide a simple and often inexpensive method to
learn the skills of ultrasound-guided needle placement, before
clinical use on patients, with the aim of reducing complications.
However, not all phantoms are equal. Do we really under-
stand what we are dealing with when using phantoms, or are
they behaving true to their definition, and the images are an
illusion of reality trying to deceive us? During the development
and testing of a new echogenic needle, the Pajunk Sonoplex
(Pajunk Medizintechnologie, Geisingen, Germany), we gained
significant experience with multiple phantoms. Using this ex-
perience, we review the types and uses of phantoms in UGRA
and highlight the benefits and pitfalls.
METHODS
The literature in this review was obtained from a com-
puter search of the PubMed database through to May 2010 using
the search terms ‘ultrasound’ and ‘phantom’ without language
restriction. Additional reports were identified from reference list
screening and review articles. Abstracts were screened for rele-
vance, and full articles obtained. Authors were not contacted for
additional information. Google Scholar was used to ensure that
articles published in online journals were also included.
Types of Phantom
Early ‘tissue mimicking phantoms’ were designed for
the calibration and testing of diagnostic ultrasound machines
where accurate representation of the sonographic characteris-
tics of human tissue was paramount. This involved controlling
the acoustic impedance and attenuation properties of the de-
sired material.
3,10Y12
In contrast, the phantoms used in inter-
ventional work, such as UGRA, need not stringently reproduce
these specific physical properties. Ultrasound-guided regional
anesthesia phantoms need to be cost-effective and replicate some
properties of human tissue such as background echogenicity,
the texture, and needle resistance or being visually opaque such
that the needle and target cannot be seen from the outside of
the phantom.
Numerous interventional phantoms have been described.
To illustrate that not all behave the in the same way, we have
prepared a series of images of 4 different nerve block needles
in 5 different phantom media and at 2 different needle inser-
tion angles (Figs. 1 and 2). All images were obtained with the
same ultrasound machine (SonoSite M-Turbo; SonoSite, Inc,
Bothell, Wash), using the same settings and depth for each
angle. Each represents the best obtainable image as acquired
and assessed by 2 senior anesthesiologists experienced in UGRA
(S.H. and G.H.).
The Pajunk Uniplex Nanoline (Pajunk Medizintechnologie)
is a regional block needle with no echogenic modifications
REVIEW ARTICLE
162 Regional Anesthesia and Pain Medicine
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Volume 36, Number 2, March-April 2011
From the *School of Medicine and Pharmacology, The University of West-
ern Australia; Sir Charles Gairdner Hospital, Perth, Western Australia.
Accepted for publication November 24, 2010.
Address correspondence to: Graham Hocking, MB ChB DMCC FRCA
FANZCA FFPMANZCA, School of Medicine and Pharmacology,
The University of Western Australia; Sir Charles Gairdner Hospital,
Hospital Avenue, Nedlands, Perth, Western Australia 6009
(e-mail: graham.hocking@anaesthesia.uwa.edu.au).
C.H.M. was responsible for the design and development of the Pajunk
Sonoplex needle (Pajunk Medizintechnologie, Geisingen, Germany).
He was excluded from the imaging process to create Figures 1 and 2.
Copyright * 2011 by American Society of Regional Anesthesia and Pain
Medicine
ISSN: 1098-7339
DOI: 10.1097/AAP.0b013e31820d4207
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and has been the standard peripheral nerve block needle in our
institution. The B-Braun Stimuplex D+ (B. Braun, Melsungen,
Germany) is an echogenic needle using a texturing method
involving indentations arranged over a 20-mm length of the
distal needle shaft. These are designed to reflect par t of the
ultrasound beam back to the probe, even at steeper angles.
LifeTech (LifeTech Inc, Stafford, Tex) developed a needle with
circumferential laser etching of the distal 12.7 mm of the shaft,
starting 3 mm from the needle tip. The Pajunk Sonoplex
Nanoline is an echogenic needle using needle surface texturing
with ‘cornerstone reflectors. Two circumferential pattern-
embossed sections, each 9 mm in length and 2 mm apart, are
arranged at the distal end of the needle. The texturing is spe-
cifically oriented to maximize the echogenicity of the needle
at steep insertion angles.
The apparent brightness of the needles in these 40 images
displays the effect of differing phantoms on needles with varying
echogenicity. Needle brightness is not simply a function of the
needle, but depends on the difference between the needle and
phantom echogenicity and the effect of image processing, in
particular, the gain setting.
The needle images at 20 degrees demonstrate that all are
easily visible at shallow insertion angles irrespective of the
phantom media. The echogenicity of even a plain needle inserted
at 20 degrees is always greater than even the most echogenic
phantom background, so the needle is visible. This finding is
also true in live human tissue
13
and is a reason why UGRA
blocks using a shallow needle approach angle have previously
been considered easiest to perform. In addition, this is why it is
misleading to demonstrate newer echogenic needles at shallow
insertion angles and in media with low background echogenicity
without providing a direct comparison.
The needle images at 45 degrees demonstrate the im-
portance of knowing the echogenic properties of the phantom
when considering visibility. The pure anechoic background of
the water phantom allows even the weakest reflection from the
needles to be seen. Hence, it even makes the unmodified Uni-
plex needle visible, and all the echogenic needles highly visible.
The gelatin phantom and pork phantom have greater back-
ground echogenicity such that the Uniplex needle is now visible
only because of needle shadowing and by the echogenicity of
the tip. Within the gelatin phantom, all the other echogenic
FIGURE 1. Ultrasound images of nonechogenic (Pajunk Uniplex) and echogenic (LifeTech, B-Braun D+, and Pajunk Sonoplex) needles
inserted at 20 degrees to the surface and 2 cm deep into a series of phantom media. Water (A), Blue Phantom (B), gelatin/Metamucil
(C), pork (D), unembalmed cadaver (E).
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needles are visible especially the LifeTech and the Sonoplex.
The cadaveric tissue with its higher background echogenicity
has made all of the needles almost invisible except for the Sono-
plex. This observation is consistent with our ongoing clinical
and cadaveric needle visibility studies.
13Y15
As explained below,
it is our belief that live human tissue is even more echogenic than
cadavers, which makes needle visibility even harder. We were
able to obtain only 18-gauge Life-Tech needles. The larger gauge
may have slightly increased the visibility of the needle, but as
nonechogenic areas of the shaft are invisible, most of the needle
echogenicity is due to their technology; hence, we felt it appro-
priate to include this new needle.
Water
Construction
Water baths can be made using any watertight container,
with or without the addition of a submerged target structure.
Using warm water that cools, and allowing the water to stand,
reduces background echogenicity to virtually zero (air bubbles
solubilize and disperse). This makes the needle and any target
placed in the bath easy to image.
Pros and Cons
Water baths provide a readily available, inexpensive, and
simple phantom. They can be used repeatedly over time with
no deterioration in image or decomposition of any synthetic
target used. A water phantom is of little use in the teaching and
practice of needle guidance, as there is no tactile feedback, and
it does not ‘fix’ the needle in place (ie, prevent translational
movement), making it difficult to keep a needle in-plane.
Recommendations
Water baths are useful during initial studies to define ideal
images and confirm relevant sonoanatomy, such as with spinal
phantoms.
16,17
Unfortunately, these convenient perfect water-
bath images do not translate well into clinical practice.
Agar/Gelatin
Construction
Burlew et al
10
described a simple recipe for use in the cali-
bration of diagnostic ultrasound machines. She added graphite
FIGURE 2. Ultrasound images of nonechogenic (Pajunk Uniplex) and echogenic (LifeTech, B-Braun D+, and Pajunk Sonoplex) needles
inserted at 45 degrees to the surface and 3 cm deep into a series of phantom media. Water (A), Blue Phantom (B), gelatin/Metamucil
(C), pork (D), unembalmed cadaver (E).
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powder and n-propanol to control the phantom’s attenuation
properties and the speed of sound through it, respecti v el y. Madsen
et al
12
described a similar phantom using gelatin as the base, along
with the addition of preservatives (p-methyl and p-propyl benzoic
acids) to reduce microbiological contamination. These designs
have been adapted for use as an ultrasound biopsy phantom and
in ultrasound-guided vascular access training.
5,18,19
Some use
gelatin alone,
2,20,21
whereas others create a visually opaque and
echogenic background by the addition of materials such as flour,
corn starch, graphite powder, or Metamucil.
19,21Y26
Metamucil is
a commercially available dietary fiber supplement (Proctor &
Gamble, Cincinnati, Ohio), and we have used this type of phan-
tom with great success in our own institution. Increasing the
concentration of gelatin increases the firmness of the phantom.
Increasing the Metamucil increases the echogenicity.
Pros and Cons
Such phantoms are relatively simple and cheap to produce;
most can be made for less than around US $35.
5,18
A 1-L gelatin
phantom can be made in 30 mins and be stored in the fridge for
many weeks. Addition of chlorhexidine solution to the surface
of the phantom further prolongs its life. Using antireflux valves
and priming the needle with fluid to remove the air can reduce
needle-tracking artifact. Air in needle tracks is mostly absorbed
with time, but persistent tracks can usually be removed by
microwaving and allowing to cool overnight, thus producing
virgin ultrasound appearances with each set up.
19,27
The addi-
tion of echogenic material provides a more realistic background
against which to image the needle and prevents the operator from
directly visualizing the needle passage in the phantom.
Recommendations
Gelatin phantoms can be constructed in layers to allow the
addition of simple or complex targets. The relatively anechoic
and transparent background of agar or gelatin enhances needle
visibility, which may assist with early learner confidence. Some
tactile needle feedback allows for practice of needle guidance.
Blue Phantom
Construction
The patented ‘Blue Phantom’ (Blue Phantom, Seattle,
Wash) is constructed from an elastomeric rubber. The physical
properties, including speed of sound and attenuation, are tailored
to be the same as those of human tissue (personal communi-
cation, Brian Keegan, www.bluephantom.com). The material
is designed to ‘self-heal’ in an attempt to minimize needle-
tracking artifact that can limit the life span of the product. When
a needle enters the material, it pushes the neighboring mate-
rial off to either side of the needle, which then rebounds to its
original location when the needle is removed. Healing occurs
because the elastomeric rubber has an affinity for itself and
thus reconstitutes when the needle is withdrawn. It is important
that only unbent and sharp 18- to 21-gauge needles are used.
The company recommend replacement of needles every 10 uses
or if they get used in material other than the Blue Phantom.
Dull or bent needles will drag the tip of the needle through the
material, causing ‘scuffing’ resulting in residual visible needle
tracks because the material is unable to properly reconstitut e.
Pros and Cons
A firm texture for needle insertion is provided, more so
than in agar and gelatin models, and targets can again be in-
corporated in to the str ucture. It is expensive compared with
homemade models (US $499), and being homogenous with low
background echogenicity, it can make needle visibility decep-
tively good. Nevertheless, this model has been the training
ground for many UGRA practitioners and has been used as the
testing medium in several needle visibility studies.
28,29
The
elastomeric rubber molds well to the ‘smooth’ shafts of tradi-
tional needles, but many of the recent echogenic technologies
depend on texturing of the needle surface. In human tissue, it is
assumed that fluid fills these indentations to achieve a tissue-
metal interface for the reflection of the ultrasound waves. In
the Blue Phantom, many of these needle texturings will not be
filled by gel, but instead remain as air pockets adjacent to the
shaft. This removes the phantom-needle interface and may alter
the echogenicity of the needle. The performance of echogenic
needles in a phantom may therefore be different to that seen in
human tissue.
Recommendations
Gelatin and Blue Phantoms behave similarly to water
baths, but th ey also provide a degree of texture that both fixes
the needle in its path and gives some element of ‘feel’ as the
needle is inser ted. Needle visi bility is high, which makes skill
acquisition easier but can lead to false confidence in regard
to clinical ability. They are useful in the early stages of lear n-
ing needle guidance, before progressing to harder targets or
meat phantoms.
Other Materials
Other low-fidelity phantoms have been described as listed
in Table 1. The features of these are similar to those already
mentioned.
Meat Phantoms
Construction
Xu et al
8
described a pork phantom for real-time UGRA
practice using an 8- to 10-hr soak in 70% alcohol to deodorize
and partially preserve the meat. We have modified this technique
using 66% alcoholic hand wash (Aqium Gel; Ego Pharmaceuticals
Pty Ltd, Braeside, Australia) to make a pork phantom for ultra-
sound-guided neuraxial block (Fig. 3).
30
This is a widely available
TABLE 1. Other Low Fidelity Phantom Media in the Literature
Phantom Material Construction
Extra firm tofu
4
Block of foodstuff T wood or wire targets
‘Premisorb’
56
Nonperishable medical solidifying agent poured into an empty crystalloid bag
Foam/saline (US patent 4286455) sponge/degassed water
35
Sponge immersed in a fluid-filled container
Commercial beef gravy
57
Mixed with 8 cups of water and kept in suspension using a magnetic stirrer
Evaporated milk (US patents 5902748 and 5625137) Mixed with water and preservative T gelatin to solidify
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source of alcohol within all areas of the hospital and is per-
fumed, which helps in the deodorizing process. Bovine extensor
digitorum longus muscle has been used successfully as an inter-
ventional phantom in a study looking at UGRA learning curves.
Turkey breasts or other media have frequentl y been used in
interventional radiology studies
21,23,24,31Y35
and more recently as
an UGRA training model.
36
Pros and Cons
The pork phantom is a moderately cheap (about US $20),
simple, and sur prisingly long-lasting model for practicing
needle visualization. Anatomic structures are clearly visualized
with background echogenicity, tiss ue layers, and needle images
comparable to those in human tissue . Tactile feedback when
crossing tissue planes mimic that felt in clinical practice, and
needle-tracking artifact is less pronounced when compared with
gel-based models, presumably because they fill with tissue fluid
after needle removal. In contrast to synthetic phantoms, hydro-
dissection and simulated local anesthetic injection can also be
performed.
37
Of the other meat phantoms, we have found beef
to be less effective because of thick adipose layers excessively
degrading the ultrasound images. Experience with turkey has
also been disappointing, as it is slippery, hard to hold in posi-
tion, and difficult to stop the tissue deforming from transducer
pressure. Tissue layers are also unlike those in humans, and the
smaller size of the animal means that deeper needle insertion
techniques are less easily practiced.
Recommendations
Meat phantoms are cheap and provide a more realistic
simulation of needle guidance in actual clinical practice. The
background, needle visibility, and tactile feedback are closer to
those of human tissue than the low-fidelity phantoms.
Cadavers
Construction
Cadavers can be fresh, fresh frozen (unembalmed), or
embalmed in a variety of solutions. Cadavers prepared using
Thiel’s embalming method produce more realistic images and
fascial ‘pop’ sensations when compared with fresh (recently
deceased) cadavers.
6
Some have also suggested they maintain
reasonable flexibility.
38
Cadaveric phantoms also permit the
injection of local anesthetic and the assessment of perineural
spread, another key component of successful UGRA.
6,38
Our
own experience developing a national UGRA workshop has
been that fresh-frozen cadavers provide excellent images and
tactile feedback.
39,40
One problem with cadavers is the absence
of normal vascular anatomyVvessels are usually collapsed. We
recently described a gelatin infusion technique in an effort to
overcome this problem and improve the realism of this model
for UGRA.
39
One fresh male cadaver was identified for perfu-
sion before being frozen. The vascular system of the cadaver
was perfused with a dyed gelatin suspension via both superficial
femoral arteries. The gelatin concentration was such that 238 g
of gelatin was added to 3 L of saline and dissolved by stirring
at 70-C for 30 mins. Alizarin red dye was added (5 mL/L) to
color the solution red for the benefit of vascular surgeons using
the cadaver subsequently. The gelatin solution was infused via
gravity feed from a height of 1 m and required 2.75 L for com-
plete perfusion. Others have used a pneumatically driven system
to generate palpable pulses in cadavers and demonstrated sig-
nificantly improved learning experience.
41
Pros and Cons
Human cadavers can be an expensive and difficult resource
to access, whether ‘fresh’ or embalmed, and there are ethical
issues to consider. However, when available, they provide an
invaluable training resource. Tsui et al
42Y44
comment on the
opportunities offered by embalmed cadavers. They describe the
imaging of ‘true’ human anatomy in a time-rich environment,
of needle insertion without the risk of clinical consequence, and
of the dissection of target tissues after needle insertion and injec-
tion. Sessions in the anatomy class are included in the recently
published Mayo Clinic UGRA training curriculum.
7
Many have
published on the benefits of regional anesthesia cadaveric
workshops,
39,40,45,46
and cadaveric experience is a pr ere quisite
for the ESRA di ploma (http://www. esraeurope.org/educati on_
diploma.asp).
Recommendations
Unembalmed cadavers are probably the closest phantom
media to live human tissue. Our gelatin infusion technique
restored the appearance of vascular anatomy and allowed more
FIGURE 3. Trainee practicing real-time ultrasound-guided
neuraxial block on a porcine phantom using a Sonoplex needle
(Pajunk Medizintechnologie).
FIGURE 4. Ultrasound image of the axillary brachial plexus in a
fresh cadaver illustrating restoration of normal vascular anatomy
following gelatin perfusion (m), ulnar nerve (u), radial nerve (r),
musculocutaneous nerve (mc), and axillary artery (a). Reproduced
with permission from Hocking and McIntyre.
39
Hocking et al Regional Anesthesia and Pain Medicine
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realistic reproduction of the expected anatomy for realistic nerve
block practice (Fig. 4).
39
Cadavers also provide a good medium
for the testing of new UGRA technology and the development of
new UGRA techniques as they more closely mimic the clinical
situation.
14
We have noticed that needles still appear more echo-
genic in cadaveric tissue compared with live human tissue. We
hypothesize several explanations for the difference. Dead cells
release their intracellular fluid, increasing the extracellular fluid
adjacent to the needle. The more watery background decreases
echodensity adjacent to the needle, hence enhancing the needle
visibility. In addition, tissue density changes when cold; the lack
of blood flow and tissue movement may all artificially improve
the ultrasound image.
Creating and Troubleshooting
Homemade Phantoms
Almost all noncadaveric phantoms have been adapted to
include targets mimicking specific tissues or pathology. The
optimal target depends on what body structure needs to be
simulated. Table 2 lists materials previously described to assist
anyone considering making his/her own phantoms. Commer-
cially produced phantoms can be costly and will still suffer
image degradation with repeated needle practice. Homemade
phantoms offer a simple, inexpensive, and flexible UGRA re-
source that should not be overlooked. Table 3 lists common
problems that need to be prevented along with solutions that
have been described.
Use of Phantoms for Education
There is emerging consensus that it is no longer acceptable
to use patients for first-time practice at needle placement.
1Y9
Time spent using phantoms is integral to virtually all published
UGRA training programs.
7,47Y49
Interventional radiologists have
previously demonstrated significant improvements in practi-
tioner confidence, in-plane needle visualization, success rate,
and safety of needle approach.
31
Published work on how to teach
TABLE 2. Methods Used to Simulate Target Structures
in Phantoms
Structure to Be
Simulated Method Used
Cysts Water-filled balloons
19,25
Tied-off surgical glove tips
19,23,32
Soft-tissue masses Olives
23,24,31Y35
Fruit/vegetable pieces
2,23,26,32,58
Glycerin suppositories
58
Foam pieces
56
Hotdog pieces
22
Pasta pieces
2,32
Synthetic beads
20
Pet food
26
Bone Animal bone*
Pork shoulder phantom
8
Synthetic spine model
16,17,27
Vessels Rubber tubing
5,18
*
Cooked penne pasta superglued together*
Perfuse vascular system of cadaver with gelatin
39
Pneumatic pump system
41
Nerves Wooden dowel
4
Electric wire
4
Metal rods
59
Spaghetti*
Bovine/porcine tendon
8,37
Ribs Rubber strips
20
Coffee stirrers
24
*From http://www.ra-uk.org/ultrasound-sig/83-simulator-for-ultrasound-
guided-blocks.
TABLE 3. Potential Problems and Proposed Solutions in the
Preparation and Use of Homemade Phantoms
Common Problem Solutions Proposed
Medium drying out Surface layer of mineral oil (eg, baby oil
19
)
Microbiological invasion 10% Formalin
18,20
10 ml Phenol/1000 mL media
32
Chlorhexidine
19
p-Methyl and p-propyl benzoic acids
12
70% Alcohol/alcoholic hand wash
8,30
Refridgeration
22,26
Nonperishable medium (eg, Premisorb
56
)
Needle tracking Attach an antireflux valve to the hub of
each needle and prime with crystalloid
Use needles with central stylets
20
Surface layer of mineral oil
(eg, baby oil
19
)
Microwave gelatin/agar models
to reform and reuse
19,27
Use meat/cadaveric phantom
(less tracking)
Lack of echogenicity Metamucil
22,23
of medium Graphite powder
19
Cornflour
24
Flour
25
Premisorb
56
Lack of visual opacity Food dye
22,56
Metamucil
22,27
Inhomogeneity
of medium
Pour the mixture down the side of the
bowl to exclude air bubbles
20
Add ice cubes/ice-cold water
while setting
25
Refrigerate to set
34
Stir mixture intermittently until firm
Use Metamucil
(maintains even consistency)
34
Incorporating targets
in gel phantoms
Form phantom in stages if using an
upright container
2,19,22
Pour 1st layer and allow to partially set
Rest target on layer
If target floats, pour a thin layer around
it and allow to partially set
Pour further layer to cover
Use a bag (‘‘Zip-lock,
23
IV fluid,
56
or barium enema bag
32
) to form the
phantom in and rotate it while cooling
Barium enema bag
32
Empty cr ystalloid bag
56
Reflection artifact from
phantom base
3-mm Ribbed rubber matting
20
or household sponge cloth placed
on/in the base during formation
2
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UGRA is expanding, with many studies using meat phantoms
as their chosen practice medium.
36,37,50
Sites demonstrated rapid
improvements in both operator accuracy and efficiency, regard-
less of pri or operator exp erience.
36
Our own experience using
a porcine phantom for pr acticing ultrasound-guid ed central
neuraxial blockade has resulted in increased confidence among
our trainees.
30
The design of homemade phantoms is flexible and can
be altered as a trainee progresses. Simple needle-visualization
models can subsequently be replaced or modified to incorpo-
rate target structures. These targets can then be progressively
decreased in diameter, and as a final step in complexity, their
orientation can be changed relative to the phantom’s scanning
surface.
4
We suggest that background echogenicity and target
depth be modified because both play a key role in the ease of
identifying both needle and target structure. All current phan-
toms, to the best of our knowledge, lack the facility to detect
needle-to-nerve contact. This remains a key safety issue with
regard to subsequent progression to clinical practice. Principles
that may prove useful in solving this issue include the comple-
tion of an electrical circuit between needle and target or the
detection of pressure changes in the target via a transducer set.
This additional level of sophistication may be hard to achieve on
a homemade phantom. Cadaveric workshops are also becoming
an integral component of regional anesthesia training.
6,7,40,42Y46
However, given the proble ms with availab ility, it se ems likely
these will be replaced with other simulators or virtual reality
devices.
48,51
Rational and ethical use of high-fidelity human
cadavers dictates that participants should already have an
understanding of the language associated with UGRA and have
obtained the basic hand-eye coordination for manipulation of
a transducer and needle. These skills can be cheaply and effi-
ciently gained o n low-fi delity phantoms.
Phantoms have also been proposed as a platform for the
assessment of trainee competence. Minimum standards could
be set, and these would need to be achieved before a trainee is
allowed to progress to performing ultrasound-guided nerve
blocks on patients.
4,7
In the evolving field of UGRA training,
some form of in vitro competency testing seems inevitable on
grounds of both patient safety and quality of care.
Technical Aspects of Needle Visualization
in Phantoms
The choice of medium in which to view a needle is fun-
damental to obtaining an accurate assessment of its likely per-
formance in clinical practice. Needle insertion angle is also
critical. Both these facts are easily explained.
Needle visibility is determined by the difference between
the background echogenicity of the phantom and the needle
echogenicity (or can be similarly explained in terms of acoustic
impedance).
52
Needle echogenicity is determined by the angle
of insertion relative to the ultrasound beam, the quality of any
echogenic needle technology used, and , to a lesser extent, needle
gauge. We illustrated this point with the series of images seen
earlier (Figs. 1 and 2). It is also worth noting that, in the less
echogenic phantom material, needles often look artificially bright
by the use of the autogain feature now available on many ultra-
sound machines. This is particularly true at steeper needle inser-
tion angles, when needle imaging in a live patient would actually
be far more challenging.
13
This effect is less pronounced in tissue
phantoms where background echogenicity is closer to that seen in
clinical practice because increased gain amplifies not only needle
signal but also background. Live human tissue still presents the
greatest challenge to needle visibility because of its high back-
ground echogenicity. Evaluation of new technology ideally should
be in live humans to remove the subtle but important bias intro-
duced by the use of phantoms and to ensure that the results are
applicable to clinical practice.
13
However, it is often difficult
to design an ethically appropriate way to evaluate needles on
patients, and we suggest the most comparable research medium
is the unembalmed cadaver.
14,15
Most needles are easily visualized at angles less than
30 degrees to the skin (Fig. 1)
13Y15,29,53Y55
; hence, the visibility
of new echogenic needles should be tested at insertion angles
greater than 30 degrees.
CONCLUSIONS
Phantoms allow repeated practice of ultrasound-guided
needle placement without risk to patients. The best option
depends on what is required. Water-bath phantoms can be good
during the development and investigation of new UGRA tech-
niques, but cannot reproduce tissue properties. Nonmeat phan-
toms often have low background echogenicity, which enhances
needle visibility. This is good when used for practicing needle
placement but becomes a problem if these phantoms are used to
evaluate needle technology. Meat-based phantoms provide more
realistic tissue feedback, permit local anesthetic injection, and
have a background echogenicity that is closer to that of human
tissue. However, they suffer from a short shelf life even with
the various methods described to preserve and prepare them.
Cadavers provide a more realistic environment for UGRA
practice, but availability is limited and can be expensive. Clini-
cians need a clear idea of what they require from a phantom
before choosing which type to use and to understand that no
current phantoms currently replicate clinical practice.
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    • "When available, they provide excellent images and tactile feedback that mimic living human tissues. They also permit local anesthetic injection and dissection of the target tissue after injection [3,12] . However, they have no normal vascular anatomy, because the vessels are collapsed. "
    [Show abstract] [Hide abstract] ABSTRACT: With the growing use of ultrasound for pain management, we are interested in how to teach and practice ultrasound-guided procedures. Ethically, we should not insert a needle in a patient until after much practice on a phantom. Several types of phantoms have been introduced for ultrasound training, including water, agar/gelatin, elastomeric rubber, and meat phantoms and cadavers. The ideal phantom is similar to human tissue, is readily available and inexpensive, can be used repeatedly, provides tactile feedback, will hold a needle in place, does not generate needle tracks, and is not a health hazard. Several studies have shown the effectiveness of phantoms for improving the proficiency of novices. We hope that the application of phantoms in education leads to improved proficiency and increased patient safety.
    Full-text · Article · Apr 2016
    • "A phantom may be described as any medium other than live human tissue that can be used for research or training. Phantoms generally provide a simple tool that can be used to learn the skills of ultrasound-guided needle placement, before clinical use, with the aim of decreasing the incidence of complications [6]. In this article, we describe a gelatin-based phantom that can be used to identify most of the common novice errors and to facilitate learning of the relevant skills. "
    [Show abstract] [Hide abstract] ABSTRACT: Training in ultrasound-guided regional anesthesia can be acquired by attending peripheral nerve block courses. The most common novice error is “advancement of needle when tip was not visualized.” The use of simulation has shown improvement in the skill and success of ultrasound-guided procedures. Phantoms provide a simple tool that aid in the improvement of such skills. We describe a gelatin-based phantom that can be easily constructed and used to identify novice errors and facilitate in learning relevant skills. The phantom can be transilluminated to identify the target and is helpful in providing real-time, immediate feedback to novices as they practice probe–needle–target orientation.
    Full-text · Article · Sep 2013
    • "Because anatomic structures of a pork phantom are clearly visualized with an ultrasound, including the background echogenicity, tissue layers, and needle images that are comparable to those in the human tissue [12], we used a boneless pork phantom (10 × 10 × 20 cm). "
    [Show abstract] [Hide abstract] ABSTRACT: Ultrasound subjective visibility of in-plane needles is correlated with the intensity difference between the needle surface and the background. Regional anesthesia catheters are difficult to visualize by an ultrasound. In the present study, we investigated the ultrasound visibility of the catheters. Six catheters were placed at 0° and 30° relative to and at a depth of 1 cm below the pork phantom surface. Ultrasound images of in-plane catheters were evaluated, subjectively and objectively. Outer and inner objective visibilities were defined as the difference in the mean pixel intensity between the catheter surface and adjacent background, and between the surface and the center of the catheter, respectively. Evaluations were made based on the portion of the catheters. A P value < 0.05 was considered significant. Subjective visibility was more strongly correlated with the inner objective visibility than with the outer objective visibility at both angles. Metallic 19-gauge catheters were more subjectively visible than the non-metallic 20-gauge catheters at 30° degrees (P < 0.01). Subjective, and outer and inner objective visibility were significantly lower at 30° than at 0° (P < 0.01, P < 0.01, P = 0.02). Perifix ONE at 0° and Perifix FX at 30° were the most visible catheters (P < 0.01 for both). Subjective visibility of catheters can not be evaluated in the same manner as that of the needles. For the best possible visualization, we recommend selecting a catheter with a structure that enhances the dark at the center of catheter, rather than basing the catheter selection on the bore size.
    Full-text · Article · Jul 2012
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