Biomedical Engineering Reference
In-Depth Information
13
Temperature Imaging
Using Ultrasound
13.1 Introduction .............................................................................................................................219
13.2 Thermal Effects on Backscattered Ultrasound .................................................................. 220
Echo Shifts and Changes in Signal Strength • Nonthermal and Unwanted Thermal Effects
13.3 Image Motion ...........................................................................................................................221
Tracking Echo Shifts • Tracking and Compensating for Real and Apparent Motion
13.4 Ultrasonic Measurement of Temperature ........................................................................... 224
Experimental Concerns • Attenuation • Thermal Strain Using Echo Shift • Change in
Backscattered Energy
13.5 Discussion .................................................................................................................................233
13.6 Summary and Conclusions ....................................................................................................233
References ............................................................................................................................................ 235
R. Martin Arthur
Washington University in St. Louis
uniformly heat tumors at therapeutic levels in patients receiving
thermal therapy.
35
Many investigators have looked at ways of measuring tem-
perature noninvasively. Possible methods include impedance
tomog raphy,
36
microwave radiometry,
37
and magnetic reso-
nance imaging (MRI).
4,38
MRI temperature imaging appears
to have the required accuracy and spatial resolution for many
thermal therapy scenarios, but it is expensive, requires a fixed
installation, and may be difficult to use along with some heating
therapies.
38
Nevertheless, at present MRI is the most advanced
clinical technology for noninvasive monitoring of thermal
therapies.
39, 40
On the other hand, ultrasound is a nonionizing, convenient,
and inexpensive modality with relatively simple signal process-
ing requirements. These attributes make it an attractive method
to use for temperature estimation if a temperature-dependent
ultrasonic parameter can be identified, measured, and cali-
brated. Methods for using ultrasound as a noninvasive ther-
mometer fall into three categories: (1) those exploiting thermal
strain, which are based on echo shifts due to changes in tissue
thermal expansion and speed of sound (SOS), (2) those that
use the measurement of acoustic attenuation coefficient, and
(3) those that exploit the change in backscattered energy (CBE)
from tissue inhomogeneities.
In this work, we explore ongoing efforts in temperature
estimation with ultrasound using shifts in echo position,
13.1 Introduction
Thermal therapies for the treatment of pathological tissues range
from freezing with cryosurgery to high-temperature ablation.
1-11
The application and impact of these methods either alone as
an alternative or adjuvant to radiotherapy or chemotherapy is
the subject of ongoing investigation.
12-19
In particular, the sig-
nificance and impact of high-temperature ablation therapies is
growing rapidly.
4, 6-9,20-24
A major limitation of thermal therapies, however, is the lack
of detailed thermal information available to monitor and guide
the therapy.
13, 14,16,25-29
Temperatures are routinely measured with
sparse invasive measurements. The limited number of measure-
ments may produce temperature distributions with less detail
than is necessary to assess thermal dosimetry properly.
16, 26
With
the advent of multi-element heating devices, there is increased
need for temperature measurements that could provide detailed
feedback about temperature distributions. This information in
near real time would considerably improve the ability to deliver
consistently effective temperature distributions.
30-34
To meet the capability of present and forthcoming heat-
ing technologies for hyperthermia, a clinically useful method
is needed to measure 3D temperature distributions to within
1°C with spatial resolution within 1 cm
3
or better. A noninva-
sive method for volumetrically determining temperature dis-
tribution during treatment would greatly enhance the ability to
219
