U l t r a s o u n d I m a g i n g • R ev i ew
Dubinsky et al.
High-Intensity Focused Ultrasound
Ultrasound Imaging
Review
High-Intensity Focused
Ultrasound: Current Potential
and Oncologic Applications
Theodore J. Dubinsky 1
Carlos Cuevas
Manjiri K. Dighe
Orpheus Kolokythas
Joo Ha Hwang
Dubinsky TJ, Cuevas C, Dighe MK,
Kolokythas O, Hwang JH
Keywords: apoptosis, coagulation necrosis, hemostasis,
high-intensity focused ultrasound, tumor ablation
DOI:10.2214/AJR.07.2671
Received December 7, 2006; accepted after revision
July 27, 2007.
1
All authors: Department of Radiology, University of
Washington, Box 359728, 325 Ninth Ave., Seattle,
WA 98104. Address correspondence to T. J. Dubinsky
(tdub@u.washington.edu).
CME
This article is available for CME credit. See www.arrs.org.
for more information.
OBJECTIVE. The objective of this article is to introduce the reader to the principles
and applications of high-intensity focused ultrasound (HIFU).
CONCLUSION. Although a great deal about HIFU physics is understood, its clinical
applications are currently limited, and multiple trials are underway worldwide to determine
its efficacy.
T
he use of ultrasound in clinical practice is no longer limited to diagnostic imaging or to simple needle
guidance in the performance of
percutaneous procedures such as amniocentesis
or tumor biopsy. Ultrasound technology now allows the use of focused ultrasound energy for
therapeutic purposes such as tissue ablation and
hemostasis. High-intensity focused ultrasound
(HIFU) is being promoted as a noninvasive
method to treat certain primary solid tumors
and metastatic disease, to ablate foci of ectopic
electrical activity in the heart, and to achieve hemostasis in acute traumatic injuries to the extremities and visceral organs.
The field of medicine is evolving toward
greater use of noninvasive and minimally invasive
therapies such as HIFU. Unlike radiofrequency
or cryoablation, which are also used to ablate
tumors, ultrasound is completely noninvasive
and can be used to reach areas of hemorrhage or
tumors that are deep within the body, provided
there is an acoustic window to allow the
transmission of ultrasound energy. Preliminary
reports suggest that there is reduced toxicity with
HIFU ablation compared with other ablation
techniques because of the noninvasive nature of
the procedure.
This article presents a review of HIFU,
including its mechanisms of action, current
clinical applications, and future requirements to expand the clinical applications of
this technique.
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0361–803X/08/1901–191
© American Roentgen Ray Society
AJR:190, January 2008
Clinical History of HIFU
As early as 1954, Lindstrom [1] and Fry
et al. [2] investigated the possibility of using
high-intensity ultrasound for treating neurologic disorders in humans. Fry and colleagues
are credited with the first application of HIFU
in humans by producing elevated acoustic
intensities in vivo by focusing ultrasound energy in a manner analogous to the way a magnifying glass can be used to focus light. In the
1970s, ultrasound was again investigated, but
at lower intensities and for treating tumors [3].
The concept was to induce hyperthermia (elevation of tissue temperature to ≈ 43˚C) in the
entire tumor volume and then maintain the tumor at that temperature for an extended time
(≈ 1 hour). Unfortunately, this strategy did
not work out, with difficulties including the
lack of a noninvasive temperature-measuring
method to use in feedback control of the delivered acoustic power to the tumor. This inability resulted in the lack of uniform heating
and maintenance of the entire tumor volume
at a temperature greater than 43˚C.
The next innovation arose in the 1980s
with the development of extracorporeal
shockwave lithotripsy (ESWL) [4]. The use
of ESWL as a method for treating kidney
stones was approved in 1984 by the U.S.
Food and Drug Administration. It was the
first clinical application of high-(pulse-averaged) intensity ultrasound. A rediscovery of
HIFU for the treatment of tumors occurred
in the 1990s with the refinement of modern
technology, in particular, advanced imaging
methods such as MR thermometry. Furthermore, the realization that HIFU can produce
almost instantaneous cell death by coagulation necrosis to selected regions of tissue
has made it a candidate for direct and rapid
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Dubinsky et al.
treatment of tumors [5–14]. Finally, not only
has tumor treatment been targeted, but HIFU
can also be used to achieve hemostasis, as
shown in animal experiments [15–21].
HIFU Overview
In comparing the differences in intensities
of HIFU and diagnostic ultrasound, HIFU has
significantly higher time-averaged intensities
in the focal region of the ultrasound transducer. Typical diagnostic ultrasound transducers deliver ultrasound with time-averaged
intensities of approximately 0.1–100 mW/cm2
or compression and rarefaction pressures of
0.001–0.003 MPa, depending on the mode
of imaging (B-mode, pulsed Doppler sonography, or continuous wave Doppler sonography). In contrast, HIFU transducers deliver
ultrasound with intensities in the range of
100–10,000 W/cm2 to the focal region, with
peak compression pressures of up to 30 MPa
and peak rarefaction pressures up to 10 MPa.
Thermal Effects of HIFU
The major effect of high acoustic intensities in tissue is heat generation due to absorption of the acoustic energy. The heat raises
the temperature rapidly to 60˚C or higher
in the tissue, causing coagulation necrosis
within a few seconds. Focusing results in
high intensities at a specific location and over
only a small volume (e.g., 1-mm diameter
and 9-mm length). This focusing minimizes
the potential for thermal damage to tissue located between the transducer and the focal
point because the intensities are much lower
outside the focal region (Figs. 1 and 2).
Mechanical Effects of HIFU
Mechanical phenomena, in addition to
thermal effects, are associated at high intensities but are not present at lower intensities.
Mechanical phenomena include cavitation,
microstreaming, and radiation forces.
Cavitation—Cavitation can be defined as the
creation or motion of a gas cavity in an acoustic field [22, 23]; for example, the oscillatory
movement of a gas-filled bubble in a liquid medium exposed to an acoustic field. Cavitation
occurs due to alternating compression and expansion of tissue as an ultrasound field propagates through it. If the tissue expansion or rarefaction pressure is of sufficient magnitude, gas
can be extracted from the tissue, resulting in
bubble formation. This bubble can then further
interact with the ultrasound field. There are two
forms of cavitation to consider. The first is stable cavitation, in which a bubble is exposed to
a low-pressure acoustic field, resulting in stable
oscillation of the size of the bubble. The other is
inertial cavitation, in which the exposure of the
bubble to the acoustic field results in violent oscillations of the bubble and rapid growth of the
bubble during the rarefaction phase, eventually
leading to the violent collapse and destruction
of the bubble. An interesting phenomenon has
been observed when inertial cavitation occurs
against a solid surface. The asymmetric collapse of a bubble near such a surface can create high-velocity liquid jets that impinge on the
surface with a force sufficient to damage metal
surfaces and disrupt cell membranes [24–27].
If inertial cavitation occurs near a cell membrane, one may anticipate mechanical, rather
than thermal, damage to the cell.
Microstreaming—Stable cavitation may
lead to a phenomenon called “microstreaming” (rapid movement of fluid near the bubble
due to its oscillating motion). Microstreaming can produce high shear forces close to
the bubble that can disrupt cell membranes
and may play a role in ultrasound-enhanced
drug or gene delivery when damage to the
cell membrane is transient [26].
Radiation forces—Radiation forces are
developed when a wave is either absorbed or
reflected. Complete reflection produces twice
the force that complete absorption does.
These forces are constant if the amplitude of
a wave is steady and the absorption or reflection is constant. If the reflecting or absorbing
medium is tissue or other solid material, the
force presses against the medium, producing
a pressure termed “radiation pressure.” If the
medium is liquid and can move under pressure, then streaming results [16].
Biologic Effects and Thermal Mechanisms
Diagnostic ultrasound has an excellent safety profile, with no clinically significant deleterious biologic effects having been reported using current diagnostic equipment. However, at
high intensities, ultrasound can result in tissue
heating and necrosis, cell apoptosis, and cell
lysis (Fig. 3A and 3B). Mechanisms involved
in HIFU-induced biologic effects are primarily caused by thermal and cavitation mechanisms, as discussed previously [22, 23].
Coagulation Necrosis
Coagulation necrosis occurs in tissue exposed to high-intensity ultrasound when the
rapeutic Transducer
T he
Imaging
Transducer
Undamaged tissue
in front of focus
Tumor
HIFU Beam
Focus
Target organ
Ablated tumor
volume (lesions)
Fig. 1—High-intensity focused ultrasound lesion formation in polyacrylamide hydrogel
containing bovine serum albumin that becomes optically opaque when denatured.
Treatment site is roughly 9 mm long by 3 mm wide.
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Fig. 2—Illustration depicts extracorporeal high-intensity focused ultrasound therapy
of intraabdominal tumor.
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High-Intensity Focused Ultrasound
temperature of the tissue is elevated to a certain level for a certain time [28]. The temperature required to induce coagulation necrosis is
time-dependent. Tissue temperature elevated
to more than 60˚C for 1 second will generally
lead to instantaneous cell death via coagulation necrosis in most tissues, which is the primary mechanism for tumor cell destruction
in HIFU therapy. Figures 3C and 3D show a
lesion with coagulation necrosis after a single treatment with HIFU in ex vivo porcine
liver. In a study performed by Wu et al. [28],
pathologic changes were reported in human
malignant tumors that were initially treated
with HIFU and then resected 1–14 days after
HIFU therapy. Tissue evaluated 1–7 days after HIFU therapy showed homogeneous areas
of coagulation necrosis with no evidence of
residual viable tumor cells. Seven to 14 days
after HIFU therapy, granulation tissue began
to replace the necrotic tissue, and the boundary area between treated and untreated tissue
was replaced by fibrous tissue.
Apoptosis
Although most initial cell death in tissues exposed to HIFU fields is caused by
cell necrosis from thermal injury, HIFU can
also induce apoptosis. In apoptotic cells, the
nucleus of the cell self-destructs, with rapid
degradation of DNA by endonucleases. The
primary mechanism of cell death by hyperthermia is apoptosis [29]. Apoptosis has
also been shown in leukemic cells exposed
to low-intensity ultrasound [30] and in leukemic cells exposed to ultrasound-induced
cavitation [31]. Apoptosis may be an important delayed bioeffect in tissue exposed to
low-energy HIFU, especially in cell types
that regenerate poorly, such as neurons.
Hence, there may be a more extensive area
of cellular death than just the target area of
the HIFU, and this mechanism might be a
potential limitation of the technique because
cell death due to apoptosis occurs at a lower
level of energy deposition than occurs during
HIFU, and tissue adjacent to the target may
be at risk from this effect [32, 33].
Nonlinear Effects of HIFU
Finally, nonlinear effects are observed at
high acoustic intensities. As a high-intensity
acoustic wave propagates through water or
tissue, the wave can become distorted so that
A
B
C
D
Fig. 3—Ex vivo porcine liver treated with high-intensity focused ultrasound (HIFU).
A, Transducer is above liver and energy is propagated down. Thermocouple is placed in focal region to measure temperature during HIFU exposure (arrow).
B, B-mode sonogram corresponding to sample in A. Hyperechoic area (arrow) corresponds to damaged tissue. Hyperecho is due to gas bubble formation from tissue boiling
in targeted region.
C, Histology from ex vivo porcine liver treated with HIFU (cross-section of single HIFU lesion) shows central region of coagulation necrosis. (H and E).
D, Corresponding viability stain shows central region of nonviable cells with margin of tissue that has some viable cells. Scale bar = 1 mm.
AJR:190, January 2008
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Dubinsky et al.
a sinusoidal wave initially generated by an
ultrasound transducer can become sawtoothshaped due to conversion of energy carried
in the fundamental frequency to higher harmonics, which are more rapidly absorbed.
This process results in more rapid attenuation of the ultrasound energy and more rapid
tissue heating. This can also have the effect
of distorting the distribution of heat production that would be predicted if nonlinear effects did not occur. A better understanding of
nonlinear effects in biologic systems will be
critical for advancing clinical HIFU.
To date, the contribution of each of these
effects remains poorly understood. Tissue
specimens obtained after HIFU ablation of
prostate gland, for example, show incomplete
destruction of tissue by coagulation necrosis
[34]; and to our knowledge no follow-up studies exist at this time to determine the ultimate
extent of tissue destruction by apoptosis. Dose
delivery to targeted tissues depends on the
transducer array, the energy input, and the tissue attenuation that occurs between the transducer and the target. With more research, it
may be possible to control which type of effect is being induced in the targeted tissues,
but for now the ablative effect of HIFU is a
combination of all of them.
Limitations of HIFU
Although it offers tremendous potential for
noninvasive therapy of malignancies, particularly those that are widespread or inoperable,
the usefulness of HIFU has limitations, and
risk is associated with its use that could result in adverse outcomes. Because HIFU is
essentially ultrasound, any artifacts related
to ultrasound would apply to HIFU as well,
such as acoustic shadowing, reverberation,
and refraction. Hence, lesions that are deep in
relation to bones, such as a liver lesion adjacent to a rib, will be difficult to treat. Gas in
bowel cannot be penetrated by HIFU just as
it cannot be with diagnostic sonography, and
these sound waves are reflected back toward
the transducer. With diagnostic sonography,
these reflected sound waves are of such low
energy that there is no adverse effect from
them. However, with HIFU, these reflected
waves are very high energy, and they can produce burns in the tissues that lie between the
transducer and the target. In our experience,
even small amounts of gas in the gastrointestinal tract can produce burns in the wall of the
bowel anterior to the gas and in the abdominal
wall musculature overlying the gas. Refraction artifacts can result in energy deposition in
194
the soft tissues adjacent to the target area, and
energy deposition can occur superficially to
the target if the ultrasound beam is not carefully focused into a small point.
The amount of energy absorbed by the tissues is essentially estimated by making the
assumption that the attenuation of the sound
waves in the soft tissues between the transducer and the target is linear. This assumption
may not always be true; and fibrotic, fatty, and
highly vascularized tissues attenuate sound
energy differently. Excessive energy absorption can lead to unpredictable distributions of
cell death [19]. Hence, targeting is of extreme
importance, which is why MRI guidance for
HIFU has initially become more rapidly accepted clinically than sonographically guided
HIFU [35]. One potential complication of
HIFU is the dissemination of malignant cells
from the shear forces generated by the procedure, but this potential complication has not
been substantiated either in vitro or in vivo
[36, 37]. Great care will be necessary in treating patients with HIFU to ensure that complications do not occur.
Imaging Guidance and Monitoring
of Therapy
Guidance and monitoring of acoustic therapy is most important to ensure that the desired region is treated and to minimize damage to adjacent structures. Monitoring using
real-time imaging, such as with sonography,
ensures that the targeting of the HIFU beam is
maintained on the correct area throughout the
procedure. Currently, MRI and sonography
are being used for guidance and monitoring
of HIFU therapy. Both methods have their advantages and disadvantages. MRI has the advantage of providing temperature data within
seconds after HIFU exposure. However, MRI
guidance is expensive, labor-intensive, and
of lower spatial resolution in some cases, although it is superior to sonography in obese
patients [35]. Sonographic guidance provides
the benefit of imaging using the same form of
energy that is being used for therapy. The significance of this is that the acoustic window
can be verified with sonography. Therefore,
if the target cannot be well visualized with
sonography, then it is unlikely that HIFU
therapy will be effective in the target region,
and it may potentially cause thermal injury
to unintended tissue. Temperature monitoring using sonography is not yet available, although sonographic thermometry is being actively investigated and a clinical HIFU device
in China has an incorporated sonographic
thermometry system [32]. In some instances
when tissue contrast is not sufficient to visualize a tumor in the background of normal tissue, elastography may prove helpful [18].
Imaging methods to assess HIFU treatment are similar to those used to assess the
response to other methods of ablation such as
radiofrequency ablation and include contrastenhanced CT and MRI. In addition, the use of
microbubble contrast-enhanced sonography
is also being examined as a method to evaluate the treatment effect of HIFU [36]. These
methods all examine the change in vascularity of the treated volume. Another method
currently being examined in oncologic applications is the use of PET to assess for changes
in metabolic activity after HIFU treatment.
Current Clinical Applications
The investigation and applications of HIFU
are growing rapidly. The major application of
HIFU clinically is for the treatment of benign
and malignant solid tumors [37–39]. Several
other potential therapeutic applications of
HIFU are being investigated, including thrombolysis [40–44], arterial occlusion for the treatment of tumors and bleeding [45, 46], hemostasis of bleeding vessels and organs [47–49], and
drug and gene delivery [50–60].
To date, studies using animals and human
subjects have been published for the treatment
of hepatocellular carcinoma (HCC), renal cell
carcinoma, pancreatic cancer, sarcomas, urinary bladder tumors, and prostate carcinoma.
HCC is rapidly becoming the most common
malignancy worldwide. Surgery, particularly
liver transplantation, offers the only real hope
for cure; survival rates are only 25–30% at 5
years. As a result, noninvasive alternatives to
surgery, such as radiofrequency ablation, ethanol injection, and HIFU, have generated increasing interest as alternative or adjunct treatments to surgery.
Animal models for the assessment of HIFU
devices have been published. Small-animal
models [11] have established that HIFU
can ablate areas of normal liver, and energy
thresholds for liver tissue destruction have
been published [17]. Further small-animal
experiments have correlated the histology of
HIFU [18] with tissue depth intensity levels
[12, 19–22, 61–64]. Pig liver specimens have
been used to show that the site for ablation can
be accurately placed [65–70].
Liver Tumors
Human studies have been performed as
well. Studies of the treatment of HCC and
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High-Intensity Focused Ultrasound
secondary liver metastases in human clinical
trials have been published [71].
Wu et al. [72] used an extracorporeal HIFU
device to treat 68 patients with liver malignancies. In 30 cases in which surgical excision
followed HIFU ablation, the tumor was totally
ablated. Subsequently, 474 patients with HCC
were treated using the same device [73]. HIFU
has also been used for palliation in patients with
advanced-stage liver cancer [74]. After treatment, 87% of patients reported symptomatic
improvement. Another study designed to assess
the safety of HIFU in the treatment of metastatic
liver cancer showed that in 20 patients morbidity
was low when compared with open or minimally
invasive techniques [75]. Wu et al. [76] randomized patients between transarterial chemoembolization (TACE) and HIFU. The median patient
survival times were 11.3 months in the combined HIFU–TACE group and 4 months in the
TACE-only group (p = 0.0042). To date, both
animal and human subject investigations show
significant promise in the treatment of hepatic
malignancies with HIFU.
Renal Tumors
As with hepatic malignancies, the mainstay
of treatment for renal tumors remains surgery,
with 5-year survival rates greater than 80%
after resection [77]. Because most renal lesions are small, a noninvasive approach for
their treatment would be attractive. Animal
models for renal tumor HIFU ablation exist and have been used to evaluate the use of
HIFU to treat these tumors [78–83]. HIFU
ablation of renal tumors in humans remains
in the early stages of clinical trials. A clinical
feasibility study using HIFU to ablate renal
tumors has been performed on eight patients
who showed histologic evidence of ablation in
the treated areas after excision; however, 10%
of patients suffered skin burns from the treatment [84, 85]. Other instances of using HIFU
to treat renal tumors in humans have been reported [86]. Wu et al. [87] described a series
of 13 patients with renal cell carcinoma. Nine
of 10 patients treated for palliation reported
a reduction in pain. No side effects occurred
after ablation using an experimental handheld
device [87]. Further investigations continue to
study the efficacy of HIFU treatment of renal
cell carcinoma for both cure and palliation.
Pancreatic Cancer
More than 32,000 people are diagnosed
with pancreatic cancer annually in the United
States and as many as 200,000 patients annually worldwide; the 5-year survival rate after
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diagnosis is less than 5% [88, 89]. Pancreatic
adenocarcinoma accounts for 5% of cancer
deaths in the United States and is the fourth
leading cause of cancer mortality.
HIFU for the palliative treatment of pancreatic cancer may be useful in patients who
develop symptoms that would benefit from local tumor control. Results from an open-label
study in China in 251 patients with advanced
pancreatic cancer (TNM stages II–IV) suggested that HIFU treatment can reduce the size of
pancreatic tumors without causing pancreatitis
and thus prolong survival [90]. An interesting
finding was that 84% of patients with pain due
to pancreatic cancer obtained significant relief
of their pain after treatment with HIFU. Initial
nonrandomized open-label human studies in
China have provided additional evidence to suggest that HIFU treatment of pancreatic tumors
indeed relieves pancreatic adenocarcinoma–
related pain and focally ablates malignant tissue
[29, 90–98]. Although HIFU is a noninvasive,
nonsurgical treatment that has the potential to
eliminate or significantly reduce pain associated
with pancreatic cancer, no rigorously conducted
prospective randomized controlled trials have
been conducted to determine whether treatment
of pancreatic tumors with HIFU will result in
local tumor response or a clinically beneficial
outcome by improving pain, functional status,
quality of life, or survival.
Prostate Carcinoma
HIFU has been used to treat prostate carcinoma and prostatic hypertrophy at a few medical centers in Europe and Japan for the past
decade. However, nearly 50% of patients with
prostatic hypertrophy ultimately needed transurethral prostate resection [99], so HIFU has
not been recommended for treatment of this
condition. Either the entire prostate is ablated
or, using sonographic guidance, a focal ablation of the tumor is performed [100]. Endorectal and transperineal treatment protocols have
been evaluated in animals and humans [101].
Such treatments are performed under general
or spinal anesthesia, and all patients have a
Foley or suprapubic catheter [102, 103] left in
place after the procedure. In general, entry criteria to qualify for prostate HIFU are quite specific, including a serum prostate-specific antigen (PSA) level greater than 15 ng/mL [104],
a Gleason score of less than 7 [105], local
disease either stage T1 or T2 [106], no known
lymph node or metastatic disease, a total prostate weight of less than 30–40 g, and a greater
than 5-year life expectancy [107] . All series
reported in these patients used decreasing PSA
values, negative repeat biopsies, an International Prostate Symptom Score [108], or quality of life index to assess outcome. Follow-up
intervals reported in these patients have ranged
from a few months to 5 years [108, 109]. In
some series, HIFU has been performed with
some success as a salvage method for incompletely treated tumor from external radiation
therapy [110, 111].
Success rates for the treatment of prostate
cancer range from 60% [5, 112] to 80% [113] of
patients being disease-free at repeat biopsy and
show a reduction of serum PSA values to less
than 4 ng/mL [114, 115]. Failure is generally
defined as positive biopsy or three consecutive
increases in PSA with negative biopsy findings [116]. Whole-gland versus focal treatment
resulted in a reduced incidence of recurrent
tumor of 35% to 17% in one series [113]; in patients not found to be disease-free, reductions
in tumor volume greater than 90% have been
reported [113]. Treatment success correlates
highly with pretreatment staging and PSA levels, with more than 90% of patients diseasefree and having PSA levels of 4 ng/mL initially
to 57% disease-free with PSA levels greater
than 4 ng/mL [117].
Complications from prostate HIFU are reported to occur with a frequency of 0–50%
[118]. Reported complications include urinary
retention, incontinence, urinary infection, impotence, chronic pain, rectal anal fistulas, and
incomplete treatment of disease [118]. Repeat
treatment with HIFU is associated with much
higher complication rates than single treatments
[118]. To mitigate urinary retention associated
with prostate HIFU, some investigators perform
transurethral resection before treatment [119,
120]; and in these patients, the length of time
indwelling catheters remain in the bladder has
been reduced from 40 to 7 days [121]. However,
long-term follow-up in these patients is still not
available, and because of the small numbers of
patients who have undergone HIFU for prostate
carcinoma, several authors have concluded that
there are still not enough data to justify substitution of HIFU for more conventional therapies,
although in short-term follow-up of up to 1 year,
data look promising [122–125]. Prostate HIFU
seems most appropriate in men older than 65
years, those who are not candidates for surgery,
and those who are obese [126].
HIFU Technology
To deposit large amounts of energy deep
into the body without causing damage to tissue
in the prefocal or postfocal region, it is necessary to use a wide aperture system that delivers
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Dubinsky et al.
acoustic energy with a beam that has a large
angle of convergence. Some units have been
produced with an aperture as large as 40 cm.
Critical to the performance of HIFU, just as
with diagnostic imaging, is the ability to obtain
an adequate acoustic window to allow propagation of acoustic energy to the target. An acoustic window is an area through which a sonogram of the structures within can be obtained.
There are a limited number of such acoustic
windows because bone, air, and gas interfere
with the propagation of ultrasound beams into
the body, thus obscuring targets beyond these
interfaces. For example, the bladder is an excellent acoustic window, and treatment results of
urinary bladder tumors with HIFU have been
published [127–131].
Three-dimensional sonography may provide information that would be valuable to the
performance of HIFU. Three-dimensional
sonography is likely to better delineate a volume of tissue to be treated than just a single
plane or orthogonal planes, and most commercially available HIFU systems display
with 2D sonography systems. Therefore, the
application of 3D sonography techniques is an
exciting area of future opportunity, especially
for HIFU treatment planning and monitoring.
HIFU has the potential to allow completely
noninvasive treatment of tumors. The main
advantage of HIFU is its ability to deposit
high amounts of energy deep inside the body
and tissue, with millimeter accuracy and little
or no damage to intervening tissue. In some
applications, no sedation or anesthesia is used
during the delivery of HIFU therapy.
HIFU is being increasingly used for limited
applications in Asia and Europe; however, these
studies have all been preliminary, and further
investigation will be necessary before the widespread use of HIFU can be recommended. With
advances in imaging and transducer technology
and better understanding of HIFU-related bioeffects, HIFU will likely gain acceptance clinically as a technique for noninvasive ablation of
tissue for oncologic applications.
Acknowledgment
We thank Marie Moffitt for her help in
preparing this article.
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(translated from Russian)
F O R YO U R I N F O R M AT I O N
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