Application of Three-Dimentional
Ultrasound in Obstetrics
Dr. N. Malhotra, Dr. J. Malhotra, Dr.
Meena,
Dr. Vanaj Mathur, Dr. B. Ahuja
Introduction
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hree-dimensional
(3-D) Ultrasound involves imaging of the distribution of unltrasonic echo
information in 3-D space, while conventional ultrasongraphy applies to this
imaging on a two-dimensional (2-D) plane. Now 3-D ultrasound is being regarded
as the future of ultrasound system after color Doppler system. Voluson 530 D,
the only real-time digital 3 D system as well as a very powerful digital CFM,
and it shows what the value of future diagnostic oriented system.1
Kretztechnik started in 1974 with the
first developments dedicated in 3-D ultrasound. A cylindric-shaped transducer
incorporating 25 elements mounted on a drum performed a volume scan consisting
of 25 parallel slices. (fig. 1)
It was in 1989 in Paris at the french
congress of Radiology when Kretztechnik presented the first commercially
available ultrasound system featuring the 3 D-voluson technique (voluson-
volume sonography). (fig. 2)
In 1991, Pretorius and Nelson, discussed
the potential advantages of 3 D ultrasound and its usefulness for fetal
studies.2 All the studies mentioned above used systems developed by
the authors. The most recent development is real-time 3 D ultrasound using a
defocusing lens, without computer processing3,4.
The 3 D—Voluson Technique
Continuous research and development of
this technology led to diagnostic applications in various medical fields. The
voluson system is based on several main components :
·
Dedicated
voluson transducers providing a fully automatic scan of a user-defined region
of the patient’s body. For different applications various transducers ranging
from 3.5 — 10 MHZ are available.
·
A
special electronic memory to store the ultrasound data as a geometrically
correct volume block .
·
A
digital 3 D scan converter for lossless & fast image processing.
Immediately after the volume scan is
finished (0.5 to 5 sec.), the monitor displays three orthogonal planes, congitudinal,
transverse and coronal planes. (Fig. 3) Each of these planes can be moved
within the volume block for detailed
analyses, either by parallel shifting
(tomographic slicing) or by rotation around any of the three spatial axes.
(Fig. 4)
Digital 3 D—Sonography
Only fully digital technology allows the
use of absolutely identical channels. Small deviations in the signal path are
enough to produce distortion and noise. Digital technology avoids weakness of
this kind and guarantees signal processing which is both looseness and
noiseless. This results in superior image quality, high reliability and the
stability of the system.
Three-Dimensional Ultrasound in
Obstetrics
Three-dimensional ultrasound with transvaginal scanning in the first
trimester.
Fetal biometry in the first trimester is
often used for the estimation of gestational age. Lasser and co-workers5
examined 144 first-trimester fetuses by transvaginal ultrasonography and showed
that gestational age can be estimated much earlier and more accurately than
with the transabdominal approach.
However, with the use of conventional
transvaginal ultrasonography, it is sometimes difficult to obtain an optimal
plane for crown-rump measurement for diagnosis. Three-dimensional ultrasound
overcomes this problem and increases the accuracy of fetal biometry. (Fig. 5)
Three-dimensional ultrasound with
transabdominal scanning in and after the late first-trimester with conventional
2 D Ultrasound Scan, a general impression of fetal posture can be obtained, but
it can not be described precisely. Surface rendering in 3 D ultrasound
overcomes this problem6, 7, 8.
Steiner and Colleagues9
determined gestational sac volume in the first trimester by tracing the contour
of the gestational sac using transabdominal 3 D ultrasound. In the late second
and third trimester, the volume of amniotic fluid decreases relative to fetal
size and it becomes increasingly more difficult to obtain 3 D images of the
whole body of fetus by surface rendering.
Fetal Head
Blaas and associates10 obtained
3 D images and calculated the volume of the brain cavities at 7-10 weeks of
gestation contours of the brain cavity were interactively drawn in successive 2
D slices and displayed as 3 D images. (Fig. 6)
Diagnosis of structural abnormalities such
as anencephaly. Encephalocele or choroid plexus cyst can be made by 2 D
ultrasound. However, the defects can be better described by displaying
orthogonal Triple planes simultaneously.11 (FIg. 7, 8)
The corpus collosum, which is difficult to
see with 2 D ultrasound, may be depicted with 3 D ultrasound by constructing a
section horizontal to the abdominal wall.12 (Fig. 9)
Abnormal development of cranial sutures is
seen in many dystrophic syndromes and metabolic disturbance. With 2 D
ultrasound, curvilinear Cranial structures such as cranial sutures and
frontanelles can not be properly evaluated. This is easier with 3 D Ultrasound
using a volume rendering method such as the maximum intensity method13
or defocusing lens (real-time 3 D ultrasound)14. (Fig. 10)
Fetal face
Three-dimensional ultrasound provides
clear surface(6, 14, 15, 16,
17, 4,
8) images of the fetal face non-invasively. Images from different
directions can also be obtained from 3 D data6, with 3 D ultrasound,
the lips18, upper gum18, nose and eyelids can be observed
well and morphological anomalies such as single hostric18, flat nose18,
proboscis19. Cleft lip17, 18, 19 hypotelorism18
or hypertelorism can be better seen with 3 D ultrasound14, 17, 8 and
a low set dysplastic ear can be readily diagnosed17. The facial
origin of a fetal teratoma was confirmed on a transparent rational display11.
Facial defects are one marker of chromosomal abnormalities20 and 3 D
ultrasound may be useful for increasing
the selectivity of screening.
(Fig. 11, 12, 13, 14)
Fetal Skeleton
The fetal skeleton can be observed by
volume rendering, with techniques such as the transparent method and maximum
intensity method11, 15, 16.
If the vertebral column is pathologically
curved laterally, it is impossible to display the whole vertebral column in one tomogram. Anomalies such as
scoliosis17, kyphosis, lordosis and spina bifida may be overlooked
by 2 D ultrasound. The advantage of 3 D ultrasound is the ability to visualize
both curvatures at the same time. (Fig. 15, 16, 17, 18)
Budorick and co-workers21
reviewed the ultrasonography of the fetal spine and pointed out that the
curvature of the spine, continuity of vertebral bodies and costovertebral
junctions could be observed more clearly with 3 D ultrasound using the
depth-cued maximum intensity method,
than with 2 D ultrasound. (Fig. 19)
The fetal thorax, ribs, vertebrae,
clavicles and sternum22 are observed with with 3 D ultrasound, which is useful for diagnosing a
small thorax and skeletal dysplasia related to pulmonary hypoplasia. (Fig. 20)
Fetal Cardiovascular System
In 3 D ultrasound examination of the adult
heart with regular rhythm, 3 D data are generally acquired over a period of
many heart beating, monitored by an electro cardiogram (ECG). Nelson and colleagues
solved this problem by using the movement of a heart wall/valve instead of the
ECG, and constructed 3 D images of the fetal heart without distortion due to
beating. (Fig. 21)
Smith and associates24
developed a 2 D array probe for obtaining 3 D data in real-time and applied it
to the fetal heart and real-time 3 D ultrasound with simultaneous multisection
display.
Fetal Abdomen
By surface rendering, abnormalities of the
abdominal wall such as omphalocele15, 17 and gastroschisis are well
demonstrated. It is possible to construct any slice nearly parallel to mother’s
abdominal wall in arbitrary section on orthogonal triple-section display, thus
making it to observe the esophageal-gastric junction and pylorus.
Three-dimensional ultrasound confirms
suspected, multicystic dysplastic kidney as well as renal agencsis and the
pelvic-ureter junction12 and
ureterovesical junctions are
easily observable.
Nagata and co-workers25
developed a method for 3 D reconstruction of the fetal stomach mathematically
from one ultrasonogram of a longitutinally transected stomach, using the
symmetry of the stomach about the central aseis. The inner volume of the
stomach can be measured directly from 3 D data.
The volume of the bladder is also
measurable.
Fetal Limbs
Surface-rendered images in 3 D ultrasound
give clear displays of distortions of
the normal anatomical axis such as club foot (talipes) equinovarus)17
and rocker-bottom feet as well as limb abnormalies such as phocomelia26
with 3 D ultrasound, fingers are well observed4, 15. It is thus
useful for detecting overlapping fingers6, polydactyly27
and syndactyly. (Fig. 22, 23)
With 3 D ultrasound, two orthogonal
sections can be displayed together. The section at the exact midpoint of the
limb can be obtained with good reproducibility. Favre and colleagues28
determined thigh circumference at the midpoint of the femur and are
circumference using 3–D ultrasound and proposed a new formula for fetal weight
estimation.
Fetal External Genitalia
External genitalia can be observed and
malformations of the genitalia such as hermaphroditism15 and
bipartite scrotum29 can be seen clearly by 3 D ultrasound. (Fig. 24,
25)
Estimation
of Fetal weight—placental weight and amniotic fluid
volume.
If the fetal volume can be Measured accurately
with 3 D ultrasound, a more accurate fetal weight estimation may be possible.
With 3 D ultrasound not-only fetal volume
but also placental volume and amniotic fluid volume could be measured in vino.
Fetoplacental circulation—
Three-dimensional ultrasound shows the
distributions of blood flow in the placenta. Thus it facilitates the diagnosis
of not only morphological abnormalities but also abnormalities of the
distribution of blood flow. (Fig. 26)
Limitations of Three-Dimensional
Ultrasound
1. The influence of movement of the object on 3
D images, distortion is caused, if fetus or mother moves during the acquisition
of 3 D data. So 3 D data acquisition should be carried out—during
periods of fetal rest. Merz &
co-workers17 state that conventional 2 D ultrasound is superior to 3
D ultrasound for the assessment of
cardiac anatomy.
2. Arifacts and other problems in two dimensions
also exist in three dimensions.
3. The three-dimensional image is not always
useful for diagnosis. In cases of severe obesity or in patients with oligo
hydramnios, fetal imaging not only with 2 D ultrasound but with 3 D ultrasound
is also difficult.
4. Preprocessing for three-dimensional image
construction is time consuming.
5. Scanning range is too narrow, only portions
of fetal images can be obtained in the third timester.
Conclusions
Three-dimensional
ultrasound is very useful diagnostic method in obstetrics. However, 3 D
ultrasound is not a substitute for conventional 2 D ultrasound and both methods
should be used together to get accurate & efficient ultrasonic diagnosis.
17
Application of Three-Dimentional
Ultrasound in Gynecology & Infertility
Dr. N. Malhotra, Dr. J. Malhotra, Dr.
Meena,
Dr. Vanaj Mathur, Dr. B. Ahuja
Introduction
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he
conventional two-dimentional (2 D) transvaginal ultrasound is a valuable
diagnostic tool in the field of gynaecology. Three-dimensional (3 D) ultrasound
and reconstruction can investigate more complicated structures and it overcomes
some of the limitations of 2 D sonography. The major advantages are—one the
ability to obtain ultrasound sections which are impossible to see on a routine
scan and the ability to perform accurate volume measurements. Once the volumes
are scanned and stored digitally, the images which may be missed easily or
visualised incompletely at conventional 2 D sonography can be identified at 3 D
ultrasound. In addition, 3 D ultrasound can help in differentiating different
uterine malformations and intrauterine pathologic lesions1-3. With
the recent advent of 3 D sonography, the diagnosis of the female genital tract
pathologies can be achieved accurately. Three perpendicular planes displayed on
the screen (Fig. 1) can be rotated simultaneously into a most suitable anatomic
orientation from any arbitrary planes. Various
imaging modes are available in the processing of 3 D imaging. Volumetry
is indicated in the measurement of the tumors or any interested organs.
Three-dimentional (3 D) ultrasound has recently been introduced into clinical
practice4, 1 in evaluation of the female
genital tract.
Advantages
Despite many recent technical improvement,
there are still limitations to the accuracy of ultrasound diagnosis in
gynaecology. Patient position and pelvic anatomy severly restrict the movements
of the transducer during the scan. This results
in a very limited number of scanning planes available for examination.
In three-dimensional ultrasonography, the images produced are spatially
oriented and allow detailed evaluation in multiple planes. One can examine
section by section at any angle, displaying the three orthogonal planes (Fig. 1) concomitantly and increasing
diagnostic accuracy & specificity.
Volume assessment rather than the 2 D length or circumference
measurements are more useful in evaluation of size of an organ or lesion.
Distance, circumference or volume measurements are accurate, precise &
reproducible with the 3 D ultrasound.
The 3 D sonography system from
Kretztechnik, Austria enables 0000measurement of tissue brightness using the
gray-level histogram5.
Use of 3 D ultrasound in routine will
increase competence, interest, safety & ease of learning. Three dimensional
ultrasound evaluations from various angles & planes makes more easy to
understand complex anatomic relationship.
It allows
an inexperienced person like the patient to understand a mental 3 D
impression of the underbying anatomy or pathologic condition without much
difficulty. Thus it makes doctor, patient conversations less frustrating &
less stressful for both.
With increasing demand of long distance
communication in real time, 3 D ultrasound may prove very useful.
Limitations
It in an expensive tool.
·
3
D ultrasound should be operated by skilled, talented & experienced
sonologist for good results.
·
Physical
barriers like severe obesity, absence of tissue border lines cause the same problems in 3 D as in 2
D imaging.
·
Patient
motion limits quality imaging.
·
For
large masses, high image storage capacity is required to store volume data
which adds to the expense.
·
Real
time scanning in 3 D is now available but the frame rates are still slow.
Despite of all the above, 3 D imaging in
very useful tool as an adjunct to B-mode imaging but it cannot replace B-mode
ultrasound.
Technique of three-dimensional sonography of
the female genital organs
Three-dimensional studies of the female
genital tract in our unit are performed using a B-mode scanner which monitors
spatial orientation of the images and stores these as a volumes set in the
memory of computer (Medison 530 3 D voluson, Kretztechnik, Austria).
Conventional & B-mode ultrasound examination is always completed first.
Once the position of organ is identified in the longitudinal plane, the
ultrasound probe is kept steady & the patient is asked to lie still on the
examination bed. The volume mode is then switched on. Three-dimensional
ultrasound volume is generated by the automatic rotation of the mechanical
transducer through 360. The acquired volume is in the shape of a truncated cone
with a depth of 4.3-8.6 cm. & a vertical angle of 90º, using the medium
line density, the typical acquisition time is around 10 sec. (Fig. 2 Machine)
The obtained volumes may be analyzed
immediately or stored and examined later. Computer-generated planar reformatted
sections are similar to images obtained by conventional B-mode 2—D sonography.
These perpendicular planes are simultaneously shown on the screen thus make
easier understanding of pelvic anatomy. The number & orientation of
reformatted planes are not limited thus providing multiple sections which could
not be obtained on a routine scan. The most useful plane is the transverse
section through the whole length of the uterus from the fundus to cervix which
cannot be seen on a conventional transvaginal scan. (Fig. 3 : Probes)
Kretztechnik, Austria (Medison 530 3 D)
utilizes a 3.5/5/0 MHZ transabdominal or a 7.5 MHZ transvaginal volume
transducer (Mechanical 3 D probe) to acquire the volume data set. (Fig. 3)
We have been mostly interested in the
measurement of endometrial volume. Three perpendicular reformatted sections are
displayed on the screen and a longitudinal plane is chosen for volume
measurements. The actual measurement is performed by delineating the whole of
the uterine cavity in a number of parallel longitudinal sections 1-2 mm apart.
Then the endometrial volume is calculated automatically by the in-built
computer software program. The 3-D reconstructed view can be cine imaged &
rotated around an axis at slow or fast speed or slice by slice to a get angle
of up to 360º usually, 25 slices of 6-7º Length around a 180º-220º angle from
the rotation centre in adequate & may take from 2-5 minutes. The newer
machines are becoming ever faster. (Fig. 4 3 D of uterine cavity)
Clinical Application of 3 D Ultrasound
Uterine Pathology
(A) Congenital Anomalies
Hysterosalpingography (HSG) is widely
accepted as a standard method for the diagnosis of congenital uterine
anomalies. It is an invasive test which requires the use of contrast medium and
exposure to radiation. Although HSG provides a good outline of the uterine
cavity, it gives no information about the outer uterine contour. Therefore, the
distinction between different types of lateral fusion disorders in impossible.6,7
Definite diagnosis can be made non-invasively with 3 D ultrasound. The
cornal/frontal section though the whole length of the uterus is most useful.
This plane, being perpendicular to the direction of the ultrasound beam spread,
can not be seen on a conventional
transvaginal scan. Jurkovic and colleagues2 have suggested
that the best time to image the uterus is in the luteal phase when the
endometrium is most thickened and echogenic. The fundal cleft and the length of
septum can be accurately measured by 3 D ultrasound & allow accurate
differential diagnosis (Fig. 5) between
an accurate, supseptate and bicornuate uterus. 3 D three-planer image of a
normal uterus is having a convex fundus and straight upper line of the uterine
cavity. An arcuate uterus has a convex fundus but concave rounded upperline of
the uterine cavity. A sepsptate uterus is identified by a septum dividing the
proximal portion of the uterine cavity but the uterine fundus is convex or with
a shallow cleft (< 1 cm). A bicornuate uterus has two well formed cornua
separated by a large fundus indentation2, 80 (> 1 cm) (Fig. 5)
An important additional advantage of 3 D
ultrasound (in comparison to HSG) is the ability to visualise and obtain clear
images of both the uterine cavity & myometrium at the same time without the
need for additional invasive testing.
The sensitivity, specificity, positive
& negative predictive values of 2 D & 3 D ultrasound for the diagnosis
of normal uterus & congenital uterine anomalies were calculated in 60
patients with technically acceptable 3 D volumes (Table 1)
Table 1
Sensitivity &
specificity of two-dimensional (2 D) and Three-dimensional (3 D) ultrasound for
the diagnosis of uterine anomalies in comparison with hysterosalpingography.
Sensitivity (%) Specificity (%) Normal uterus
2 D 88 94
3 D 98 100
Arcuate
uterus
2 D 67 94
3 D 100 100
Major
anomaly
2 D 100 95
3 D 100 100
Two-dimensional ultrasound detected all
cases of anomalies but there were a number of false-positive findings. The
lateral parts of the uterine cavity close to the tubal origin gave a false
impression of an arcuate uterus. In these cases a division of the endometrial
echo in the lateral uppermost part of the uterine cavity was seen. Due to
inability to obtain transverse section through the long axis of the uterine
fundus. The distinction between normal & arcuate uterus is often impossible
on conventional B-mode scanning. Similarly the diagnosis of different anomalies
like subseptate & bicornuate uterine cavity is based on the accurate
measurement of the fundal cleft & the length of the Septum. These measurements
could not be performed on a traditional scan. The sensitivity of 2 D ultrasound
is very high & therefore it can be used as a screening test for congenital
uterine anomalies. Three-dimensional ultrasound is used as a diagnostic test in
those with a screen positive result on 2 D scan.
(B) Leiomyomas & Adenomyosis
3-D ultrasound can be used to asses the
volume of uterine myomas or adenomyosis. Serial slices across the lesions are
taken for measuring the total tumor volume. Hysterosalpingography can delineate
submucous fibroids as filling defects but the exact position of the fibroid is
often unclear. 3-D ultrasound can provide accurate diagnosis, localization and
measurement of any uterine leiomyoma.
Endometrial Pathology
Endometrial polyps, submucus fibroids, synechia,
carcianoma detection.
The feasibility of three-dimensional
reconstruction of the endometrium cavity was initially shown by Balen &
coworkers, & subsequently by many investigaters.2, 3, 10, 11
Three dimensional scanning provides the more accurate size, depth &
orientation of the lesion. In most cases, saline enhancement & 3 D images are essential to
assist in specific presumptive diagnosis. (Fig. 6)
The technique of 3 D—Saline contrast
hysterosonography (3 D—SHSG) has been
described by Weinraub’s group.11 After performing 2 D transvaginal
ultrasound for screening, a speculum is placed & the vagina cleansed with
an antiseptic solution (providone-iodine). A pediatric foley’s cather in
inserted into the uterine cavity. The foley’s catheter’s inflated balloon will
prevent it from the displacement during 3 D ultrasound examination. Saline must
be instilled slowly to obtain a clear view and to avoid discomfort felt by the
patient. (Fig. 7)
In postmenopausal women with cervical
stenosis, a simple insemination catheter can be used to minimize discomfort. The 3 D TVS probe is
reinsterted posterior to the catheter,
volume images obtained with the probe held still & patient not breathing
for approximately 10 seconds. Then the probe can be removed and images stored
for evaluation of the endometrial canal. (Fig. 8)
Uterine polyps are seen as echogenic
protrusions on a stalk, uterine submucus myomas are seen as broad-based
protrusion into the endometrial cavity with mixed echogenicity. Uterine
synechia appear as irregular multiple echogenic bands. Endometrial cancer is
seen as an endophytic intracuminal growth. (Fig. 9, 10, & 11)
Bonilla Musoles12 and his
coworkers have shown that results of 3 D - SHSG correspond to hysteroscopy as
well as histopathological tissue diagnosis. Small submucus myomas & polyps
(few millimeters) can be visualized clearly by 3 D ultrasound. Differentiation
between intramural and submucus fibroid may help in deciding the treatment
modality. Better visualization of Myometral invasion in patients with
endometrial cancer was seen with 3 D13 ultrasound. It may allow
noninvasive staging of endometrial cancers. (Fig. 12)
Endormetrial Cancer Screening
Endometrial thickness of less than 5 mm by
conventional 2 D TVS is associated with atrophic or normal endometrium in over
96% of cases10,14. However there is significant overlap in
endometrial thickness measurements between, hyperplastic, polypoidal and
cancerous endometrium. Volume is superior to endometrial thickness in the
evaluation of abnormal uterine bleeding and screening for endometrial cancer
(Table 2)10.
Gruoeck and coworkers10 found
significant differences in the mean volume measurements between polyps (2.4
ml. SD 1.86) and hyperplasia (8.O ml, SD
7.81) while the endometrial thickness was not different (15-3 versus 16.0 mm, P
> 0.05). Volume of endometrial cancer correlated better with the stage of
the cancer and was a significant prognostic factor independent of tumor grade
or myometrical invasion.
Table—2
Endometrial
thickness versus volume in the diagnosis of cancer.
Sensitivity Specificity Positive predictive value
Endometrial
Thickness 15
mm. 83.3% 88.2% 54.5%
Endometrial
Volume 13 ml 100% 98.5% 91.7%
Intrauterine Device Localization
Transvaginal
sonography has been utilized to determine or verify the location of an
intrauterine device (IUD) after insertion or if symtoms of abdominal pain,
inability to feel the thread or amenorrhea occur. Two-dimensional ultrasound
allows only limited visualization of the IUCD. Lee and colleagues have shown
that in 95% cases, the IUCD can be visualized to its full extent by 3 D
ultrasound which is impossible to obtain on conventional ultrasound. Incomplete
opening of one arm or downward displacement of the IUCD can be easily
demonstrated by 3 D ultrasound. (Fig. 13)
Ovarian Pathology
The ovaries can
usually be visualized by transvaginal ultrasound easily. The 3 D ultrasound can
further localize the largest dimension of the ovaries in the three planes
through rotation of the stored images. Sometimes, it is difficult to localize
the ovaries because of their small sizes with no obvious follicles. The
detailed search after the documentation of target box scanning with 3 D
ultrasound can localize the ovaries. (Fig. 14)
Ovarian Cysts/Tumors
There is no good
clinical or biochemical marker to differentiate between a benign &
malignant ovarian cyst. Ultrasound has been used with increasing frequency and
multiple scoring system utilizing macroscopic characteristics (papillary
projections, septations thick or thin, echogenicity-homogenous or
nonhomogenious, consistency-cystic, solid, loculated) to assign a higher risk
of malignancy.12, 17
The papillary
projection inside the tumor and changes of tumor capsule observed by 3 D
scanning facilitates the correct diagnosis of ovarian malignancy. The tumor
dimensions, areas & volume can also be calculated with 3 D ultrasound
volumetry system. Bonilla-Musoles & colleagues found that it was much
easier to study tumor wall regularity/irregularity. They detected 7% more
papillary projections with 3 D TVS when compared to 2 D-TVS. In addition, their
ability to detect tumor infiltration through the capsule was very impressive
& may have significant clinical value in the future. The examination can be
completed in seconds but stored data can be analyzed meticulously slice by
slice without patient’s presence. Dermoid tumors are difficult to diagnose as
they have a variable ultrasound appearance. The 3 D plastic images make easier
to differentiate between teeth, bones and areas of calcification & label as
benign tumor where as on 2 D only a solid core of increased echogenicity is
seen.
Bonilla-Musoles
and colleagues18 have reported
that clots in endometriomas can be better defined on 3 D while they
could be mistaken for papillary projection on 2 D. Utero-ovarian adhesions
associated with endometriosis can be visualized with 3 D ultrasound, they were
able to identify a solid mass as a hemorrhagic corpus luteum cyst rather than a
neoplasm. In addition differentiation luteum follicular & corpus between
cyst cyst is made simple.
Multi Follicular Ovary (MFO) &
Polycystic Ovary (PCO)
Multiple cystic
changes in the ovaries are associated with menstrual irregularity and
anovalation. The follicles without increased echogenicity of ovarian stroma are
seen in the patients with MFO. However, the cyst in PCO usually demonstrate
characteristic peripheral subcapsular follicles. The ovarian and stroma volumes
and stromal echogenicity are increased apparently. Therefore, the advantage of
3 D scanning in volumetry is to provide a convenient method to calculate the
ovarian volume. 3D ultrasound can identify the characteristics for differential
diagnosis between MFO and PCO. (Fig. 15)
Ovulation Inductions
3 D ultrasound
can accurately measure the true volume of ovarian follicles in follicular
development of assisted reproductive therapy (ART) cycles. Kyei-Mensah et al
have used 3 D transvaginal ultrasound to scan the ovaries immediately before
the procedure of follicular retrieval or assisted reproduction19.
The volume of follicular fluid aspirated is more identical with that of 3 D
ultrasound, than that of 2 D ultrasound system. Thus, 3 D ultrasound is
essential tool for monitoring follicular development during ART cycles.
Three-dimensional ultrasound can accurately scan the largest dimensions of the
follicles which is critical for the timing of
human chorionic gonadotrophin (HCG) injection. Bonilla-Musoles and
colleagues18 have shown that the cumulus oophorus can be easily
edentified with 3 D TVS. In addition, the imaging of Ovarian hyperstimulation
syndrome (OHSS) can also be reconstructed by 3 D transvaginal ultrasound, to
see for the exact volume of the enlarged ovaries.
Accurate
folliculometry is crucial to the safe and effective management of ovulation
induction cyeles. and thus improve pregnancy rates. Here 3-D scanning proves to
have a definite advantage.
Cervix
The cervix
usually can not be visualized well using the transvaginal approach. It is
better to place the transducer in lower vagina without contact with the cervix.
Cervical length and the degree of cervical dilation can be clearly measured
with the aid of 3 D ultrasound after localization of cervical length.
Shortering of cervix and changes of lower uterine segment can be detected early
by 3 D ultrasound & thus prevent preterm labor due to cervical
incompetence. The application of 3 D ultrasound during the menstrual cycle can
also reveal the dilated cervical canal with cervical mucus to confirm the
ovulation event. (Fig. 16)
Adnexa
The fallopian
tubes usually can not be visualised with transvaginal ultrasound, even using 3
D ultrasound. They can be seen only in hydrosalpinx or with the presence of
cul-de-sac fluid. When there is no intrauterine sac after a period of
amenorrhoea by 2 D ultrasound, the small ectopic gestational sac could be noted
in the asymtomatic patients as early as possible by using 3 D transvaginal
ultrasound20. The senstivity of picking up ectopic gestations will be more by
using 3 D.
Conclusions
& Future Applications
Three-dimensional
ultrasonography is an exciting and rapidly developing field, providing images
of the target organ in multiple tomographic sections. In particular, for the
first time, the volume of the target organ can be accurately measured, regardless
of its shape. Three-dimensional ultrasound and reconstruction is a safe and
noninvasive technique for the assessment of internal genital organs. It shows
several advantages over the conventional 2 D scanning. The imaging of 3 D
ultrasound allows physicians to understand and appreciate the complex anatomy
of the pelvis with ease. However, it is rather time consuming and it needs
experience to use 3 D ultrasound sophisticatedly21.
Future
modifications of 3 D ultrasound in the field of infertility could include a
combination with Color Doppler ultrasound to give an index of vascular changes,
3 D real-time ultrasonography and direct quantitative computation of the volume
off target. It’s likely that 3 D ultrasound will be accepted in the future as
the diagnostic gold standard for the female pelvis.
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