Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_585_Библиотеки_им_академика_М_И_Перельмана.pdf
2 Application ofMulti-slice Spiral CT andMRI inBiliary Surgery
Fig. 2.8 Type III
ab
23
c
Fig. 2.9 (a–c) The proximal part of the cystic artery supplying the upper part of the common bile duct
24
Fig. 2.10 Branches of the right hepatic artery supplying the upper part
of the common bile duct
S. Zheng et al.
Fig. 2.12 Branches of the common hepatic artery supplying the upper
part of the common bile duct
Fig. 2.11 Branches of the hepatic artery proper supplying the upper
part of the common bile duct
plying the upper part of the common bile duct is relatively
high. The initial segment of the cystic artery often accompanies the upper part of the common bile duct, and the journey
is often short. The operation of independent cholecystectomy
or common bile duct surgery has little impact. When ligating
the cystic artery and transecting the upper part of the common bile duct simultaneously, small blood supplying arteries
should be protected to avoid damage to the very fragile arterioles trunk; when the cystic artery originates from the gastroduodenal artery, the course of its accompanying upper
common bile duct is relatively long. In the cholecystectomy,
Fig. 2.13 Branches of the left hepatic artery supplying the upper part
of the common bile duct
the proximal segment of the cystic artery should be preserved.
MSCTA does not show the problem of blood supply to the
posterior portal artery mentioned in many literatures, which is
probably because the vessels are too thin or there is no surgical conrmation. In a nutshell, the arteries supplying the
upper part of the common hepatic duct/common bile duct are
thin, with an unpredictable shape. Therefore, it is inadvisable
to separate and ligate small vessels in this area blindly.
2 Application ofMulti-slice Spiral CT andMRI inBiliary Surgery
25
At present, the biliary tract imaging technique of the 3D
Visual System (3DVS) has been applied to clinical practice;
however, successful acquisition of high-quality submillimeter
CT data is the key to processing high-quality 3D images. In
terms of scanning methods, it is vital to accurately grasp the
scanning time of the arterial phase, portal venous phase, and
equilibrium phase. The use of the bolus-triggering technique
is recommended; besides, doses of contrast agent should be
strictly calculated based on the patient’s weight. The above
two aspects are critical factors for enhanced scanning to
obtain high-quality thin-section data. In particular, since
there are individualized differences in the pathological
changes of patients with tumors in the lower part of the common bile duct and periampullary carcinoma, CT data directly
affects the quality of the model reconstructed by
MI-3DVS.Nothing but strict and standardized examination
can provide accurate and high-quality CT data for the processing of digital medical software conducive to surgical
planning, surgical risk assessment, surgical procedure demonstration, and clinical teaching.
2.3 Application ofMRI Technique
inBiliary Surgery
The Magnet
The main magnet produces an intense and stable magnetic
eld. Currently, the most widely used type is the superconducting magnet. The superconductive coil constructed with
nickel–titanium alloy is immersed in liquid helium in a
favorable low-temperature environment. The wire has no
electric resistance in its superconducting state and therefore
can create intense magnetic elds through the closed coil.
Compared with permanent magnet type and normally conductive type, the superconductive type has the advantages of
producing high-intensity and high-stability magnetic elds.
The intensity of a magnetic eld measured in Tesla (T), is a
major measurement of magnetic eld strength. The earth’s
magnitude of geomagnetic intensity at the north and south
poles is roughly 0.7 gauss (G). The conversion relationship
between Tesla and Gauss is 1T = 10,000G. The magnetic
eld strengths of the permanent magnet type and the normally conductive type are mostly less than 0.5T, and the
superconducting magnet mostly ranges from 1.0 T to
3.0T.Besides, MRI demands a high degree of homogeneity
of the main magnetic eld because the magnetic eld homogeneity is critical for spatial positioning of the MRI signal,
improving signal-to-noise ratio and reducing image artifacts
(Andrew 2016).
2.3.1 Basic Principles ofMRI
When X-rays and CT penetrates through the human body,
the density difference caused by attenuation coefcients of
various tissues is formed. In adjacent organs or tissues with
similar density, a sharp contrast image cannot be formed.
MRI is a medical imaging process that uses different chemical information emitted by tissues. The MR image displays
not only morphological but also functional changes of tissues and organs, thus providing biochemical information and
dynamic quantitative data. Modern Medicine has put forward higher requirements for Imaging, and its goal claims to
be comprehensive, rapid, accurate, and non-invasive.
Imaging is playing an increasingly important role in modern
medicine, and thus MRI shows distinct advantages for the
diagnosis of diseases. As an integrated part of medical imaging, MRI has developed rapidly in recent years. Its development represents a huge milestone for the medical imaging
world. The modality of MRI is continually advancing from
morphologic to functional diagnosis, and from static imagebased to continuous lm image or dynamic image-based
diagnosis, while morphologic diagnosis remains an essential
component in clinical MRI.
2.3.1.1 MRI Devices
The major components of a medical MRI scanner include the
main magnet, gradient system, radiofrequency system, computer systems, and other auxiliary equipment.
The Gradient System
The gradient system consists of gradient ampliers and
three sets of gradient coils in the X, Y, and Z directions. The
primary function of gradients is to modify the main magnetic eld and generate a gradient magnetic eld for spatial
encoding of the MRI signal. The key parameters to determine the gradient of the magnetic eld are intensity and
slew rates. Gradient strength refers to the difference in magnetic eld strength per unit of distance. The typical units are
expressed in millitesla per meter (mT/m). Images with a
smaller number of pixels and higher spatial resolution are
sharper and require a higher magnetic eld gradient. Slew
rates of the gradient magnetic eld refer to changes in the
gradient eld strength in unit time and unit distance. The
typical units are expressed in mT/m/ms. High slew rate and
high gradient eld strength help to shorten echo times,
speed up signal acquisition, and increase image signal-tonoise ratio.
The Radiofrequency System
The radiofrequency (RF) system consists of an RF transmitter, an RF amplier, and RF coils. The transmitter emits
radiofrequency pulses in the form of electromagnetic
radiation, permitting exciting low energy protons to transition to higher energy levels, and causing phase synchronization of the protons (The protons do not run parallel to the
magnetic eld lines, but rather undergo a rotating motion,
which is called precession).
26
short T2
100%
TE long T2 time(ms)
short T1 long T1 time(ms)
100%
S. Zheng et al.
Radiofrequency Coils
Radiofrequency (RF) coils are essential components of an
MRI scanner and the key element for imaging. The performance of transmit coils is related to data acquisition of MRI,
and the basic goal of receive coils is to achieve the highest
signal-to-noise ratio (SNR). The development of phased
array coils is considered a milestone in RF coil technology.
Phased array coils consist of several smaller coils that are
grouped together into a coil unit, and it requires multiple data
acquisition channels to match with it. Phased array coils
have the following advantages: large region of sensitivity
and high SNR; enhanced image quality in thin- slice scanning, high spatial resolution scanning and low eld strength
machine MRI; improved signal acquisition speed; small
coils can be used individually or simultaneously (Grover
etal. 2015).
The Computer System
The computer system controls all the work of the MRI scanner, including RF pulse excitation, signal acquisition, data
operation, image recombination, and processing. MRI scanner upgrade is closely related to the development of computer science. The rapid development of contemporary
computer technology enables a huge leap forward in upgrading of the MRI software, with new possibilities to expand the
use of MRI.
• When the RF pulse is turned off, the excited hydrogen
nucleus gradually releases the accumulated energy, and
its phase and energy level begin returning to its equilibrium state. This process is called relaxation, just like a
tensioned spring will quickly return to its original shape
after the external force is removed. Relaxation is the process of releasing energy and producing MRI signals. It
consists of two simultaneous and independent processes:
longitudinal relaxation and transverse relaxation.
Longitudinal relaxation: after the RF pulse is turned off,
excited protons spontaneously release energy and fall
back from the high to the low energy states under the
action of the main magnetic eld. The longitudinal magnetization vector gradually increases and recovers to its
initial equilibrium. The process is called longitudinal
relaxation. The time required for the magnetization to
reach 63% of its initial value is called the longitudinal
relaxation time, or designated T1 (Fig.2.14). Transverse
relaxation: after the RF pulse is turned off, the synchronization of protons is lost. The protons in the same direction
disperse, causing the transverse magnetization vector to
decay from maximum to zero, which is called transverse
relaxation. The time required for the transverse magnetization to decay from maximum to 37% of the initial magnetization is called the transverse relaxation time, or
designated T2 (Fig.2.15).
Other Auxiliary Equipment
MRI auxiliary equipment mainly includes the scanner table,
patient-positioning system, operation console, cooling system, air conditioning unit, system for image transmission,
lm storage and processing, and physiological monitoring
equipment.
2.3.1.2 Basic Principles ofMRI
• The study object of MRI is the proton. The atom comprises a central nucleus and orbiting electrons. The
nucleus contains positively charged protons. Protons precess around the axis, similar to the way planet earth moves
around the sun. This interaction with the proton’s magnetic eld creates magnetic resonance. Normally, the
direction of the magnetic eld produced by protons in the
body is random.
• When the patient is placed inside a large magnet, the protons’ axes in the body all lineup. Protons in the body align
with the main magnetic eld. Slightly more than half the
protons are aligned with and the rest are aligned opposite
the direction of the magnetic eld, and thus creating a net
longitudinal magnetization vector.
• A radiofrequency pulse at the same frequency disrupts the
magnetic eld direction of protons, and thus creating a net
transverse magnetization vector.
37%
0%
Fig. 2.14 The longitudinal relaxation time
63%
Fig. 2.15 The transverse relaxation time
2 Application ofMulti-slice Spiral CT andMRI inBiliary Surgery
27
T1 and T2 reect tissue characteristics, not the absolute
value. T1 is the parameter that describes the speed of longitudinal relaxation of tissues. Relaxation speeds vary in different
tissues, resulting in different T1 values. Different T1 values of
various tissues are the basis on which MRI can distinguish
different tissues. The main factors affecting T1 are tissue
composition, structure, and magnetic environment, and T1 is
also related to the intensity of the external magnetic eld. T2
is the parameter that describes the speed of transverse relaxation of tissues. The relaxation speed of different tissues varies, so T2 values of various tissues are different. By use of this
principle, normal tissue from pathologic tissue can be differentiated. The main factors affecting T2 are the external magnetic eld and the homogeneity of the magnetic eld within
the tissue (Nitz 2006).
• The analog signals are converted into a digital form by
computers with an analog-to-digital (A/D) converter, and
the digital signal is converted back into an analog form
(images) with a digital-to-analog (D/A) converter.
2.3.2 MRI Examination ofBiliary Tract System
2.3.2.1 MRI Preparations
Patient Preparation
• Patients fast at least 6h prior to MR imaging; if necessary,
negative gastrointestinal contrast agent should be administered orally (such as ferric ammonium citrate in an
effervescent tablet solution, 100ml warm water+2ml of
Gd-DTPA solution).
• Remove supercial metallic foreign bodies.
• Explain the examination procedure and train the patient to
hold breath.
Coils andPatient Positioning
• Coils: Phased-array surface coils for abdominal imaging.
• Patient positioning: The patient lies supine on the scanning table and a coil is centered at the midline of the table.
The mid-sagittal plane is aligned with the longitudinal
center of the coil, and a respiratory gating is placed below
the costal margin. Instruct the patient to breathe quietly
and regularly. The collection center is aligned with the
xiphoid process.
2.3.2.2 Regular Scan Sequences
Conventional Cross-Sectional T1W1 andT2W1
Sequences
It refers MRI scanning covering the liver, gallbladder, pancreas, and spleen. T1W1 is based on either a gradient echo or
a spin echo. If the patient breathes evenly, a respiratory-trig-
gered fat-suppressed turbo spin-echo T2W1 is preferred; if
the patient cannot breathe regularly, but can hold their breath
well, the use of single-shot turbo spin-echo T2W1 sequence
in combination with fat suppression technology can be
adopted. The conventional slice thickness is 5–8mm, and the
slice interval is 20%–30%. Small lesions can be scanned
without intervals at a slice thickness of 1–2mm.
Single-Shot Turbo Spin-Echo Coronal Sequences
The oblique coronal position parallel to the common bile
duct is often used, which can clearly display the relationship
between the common bile duct and its surrounding tissue
structures.
2D or 3D T2W1
The current protocols often use a two-dimensional singleshot fast spin-echo sequence. The common bile duct is found
on the horizontal axis image; centered around it, thick slice
imaging can be conducted in multiple directions, with a
thickness of 30 ~ 60 mm. Thin-slice coronal scanning is
adopted in 3D imaging, acquired images are reformatted
using maximum intensity projection (MIP).
Transaxial Single-Shot Turbo Spin-Echo Fat Suppression Sequences
On the basis of coronal single-shot turbo spin-echo sequences
and MRCP, an axial scan is performed at the obstruction
level, using the respiratory triggering technique. The scanning range includes the upper and lower obstruction points.
Dynamic Enhancement Sequence
A dynamic enhanced scan is required when tumors or tumorlike space-occupying lesions cannot be diagnosed. It can
improve the lesion detection rate and qualitative accuracy.
The principle of contrast-enhanced MRI similar to that of
contrast-enhanced CT, is to display contrast enhancement of
pathology or anatomical structures (the increased signal
intensity). In clinical practice, extracellular contrast agents
such as gadolinium-diethylenetriamine pentaacetic acid
(Gd-DTPA) are often used as contrast agents. These agents
have paramagnetic effects and are administered intravenously
at a dose of 0.1mmol/ kg and at a ow rate of 3ml/s. They are
used to shorten the T1 and T2 relaxation times (mainly for T1
relaxation time of tissues). T1W1 signal in spin-echo or gradient-echo sequence can be increased. Dynamic contrastenhanced MRI enables repeated imaging in the same
breath-holding state following contrast agent bolus administration. The time interval is determined according to the specic situation. Breath-holding scans can eliminate respiratory
motion artifacts. In the case that the patient breathes evenly,
and time is sufcient, scanning without breath holding combined with respiratory triggering setup is acceptable. Another
type of commonly used contrast agent in clinic is hepatobili-
28
S. Zheng et al.
ary-specic contrast MR agents, such as gadolinium ethoxybenzyl-diethylenetriaminepentaacetic acid (Gd-EOB-DTPA)
and gd-benzyloxypropionictetra- acetate (Gd-BOPTA), which
have all the functions of Gd-DTPA and hepatocyte-specic
contrast agent. They can reect both the blood supply and the
uptake function of the lesion, thus providing more information for the clinician and improve the condence of diagnosis.
In general, hepatocyte- specic contrast agents are not taken
up by non-hepatocyte- derived liver lesions, so the liver-tolesion contrast is signicantly enhanced after injection of the
medium. Thus, more lesions can be found, which is conducive to the formulation of surgical plans. Hepatobiliaryspecic contrast agents can also be used in cholangiography,
which can effectively differentiate the lesions inside and outside the bile duct and have obvious advantages in the diagnosis of postoperative bile leakage.
2.3.2.3 Special Scan Sequences ofBiliary System
Magnetic resonance cholangiopancreatography (MRCP) is
the most commonly used and most reliable method in MRI
hydrography. MRCP exploits bile as a contrast agent by
acquiring the images utilizing heavily T2-weighted
sequences combined with fat suppression technology. The
stationary uid-lled structures in the abdomen such as
intrahepatic and extrahepatic biliary trees, gallbladder, and
pancreatic ducts appear hyperintense, while the surrounding
substantial organs and blood vessels containing owing uids have low intensity and appear black. The anatomical
images of the pancreatic bile duct are subsequently reformatted by maximum intensity projection (Fig.2.16).
The requisite condition to obtain a high-quality MRCP
image is highlighting the difference in signal intensity
between the area of interest and the background. Usually, a
long TR (4 times the maximum tissue T1) and long TE
sequence can be used, which results in obvious attenuation
in the signal of soft tissues in the background. This leads to
increase in signal contrast between the background soft tissues and the static uid, thus enhancing spatial resolution.
In clinical practice, MRCP usually has three imaging
methods:
3D Volumetric Acquisitions
The use of fast spin-echo sequences with long echo train
length or single-shot turbo spin-echo sequence in combination with respiratory triggering technology, are adopted for
3D volumetric acquisitions to obtain thin multi-slice images.
The acquired images can then be reformatted using Maximal
Image Projection (MIP).
Advantages
The original thin-slice images are benecial to display small
lesions in the cavity for better reconstruction effect.
Disadvantages
Relatively long scanning time.
2D Continuous Thin-Slice Scanning
Single-shot turbo spin-echo T2W1 sequence plus segmented
K-space imaging are used to speed up data acquisition; fat
suppression technology is used to enhance tissue contrast.
Advantages
• The original thin-slice images can be achieved, which is
benecial to display small lesions in the cavity.
• The image can be post-processed in various ways.
• The time required for scanning is relatively short.
Fig. 2.16 MRCP imaging of normal intrahepatic and extrahepatic bile
ducts
Disadvantages
• The slice thickness of images is larger than that of origi-
nal images collected by 3D.
• Inaccurate image registration may occur because of poor
breath-holding or image distortion, thus affecting the
quality of 3D reconstructed images.
2D Thick-Slice Projection Imaging
The thick-slice block with a volume of 2~10cm is excited
and collected, and a projection image of the thick layer block
is obtained by one scan.
Advantages
• Only several seconds are needed for an image to be
scanned.
• The pipeline structure shows good continuity and step-
ladder artifacts are rare.
2 Application ofMulti-slice Spiral CT andMRI inBiliary Surgery
29
Disadvantages
• The image cannot be post-processed.
• Original thin-slice images cannot be obtained.
• Small lesions are easily omitted.
In clinical practice, it is better to combine two or more
above-mentioned methods with conventional MRI images.
MRCP makes use of contrast agents to produce detailed
pictures of ducts and organs. The produced images can be
processed by multiplanar 3D reconstruction and the shape of
the pancreaticobiliary tract can be clearly observed. The
images can clearly display (a) the shape of obstructed end
and state of the proximal hepatic bile duct branch of the
obstruction, and (b) the variation and malformation of the
biliary tract and biliopancreatic convergence abnormalities.
Biliary dilatation is not affected by the pressure when injecting contrast agent, reecting the true diameter of the cavity,
without serious complications, and independent of technical
operations. The disadvantages include:
• The spatial resolution is insufcient and the microstruc-
ture of pancreatobiliary tract cannot be displayed.
• Lesions with weak signals in the bile duct cavity (such as
sediment-like stones, small lumps) are easily obscured
during image reconstruction.
• It is difcult to differentiate between bile duct lesions,
including cholangiolithiasis, bubbles, polyps, and
granulomas.
• It is susceptible to intestinal effusion and ascites. MRCP
cannot display bile duct wall as well as the extent of inva-
sion and distant metastasis of extraluminal pathologies,
nor provide comprehensive imaging information. It must
be combined with conventional thin- layer original image
and enhancement examination.
MRCP is accomplished by magnetic resonance hydrography of the shape and course of the pancreaticobiliary duct.
When the lumen is completely wrapped by surrounding
bile, showing a lling defect, the image is not clearly displayed, and the detection rate of stones is reduced.
Therefore, the reconstructed image and original image of
MRCP should be integrated for analysis in clinical examination; especially in small and sediment-like stones, blurring details in image reconstruction should be avoided so as
not to affect the diagnosis. MRCP has a high diagnostic
accuracy for the detection of choledocholithiasis and it can
replace invasive and radiative diagnostic methods such as
percutaneous transhepatic cholangiography (PTC) and CT
colonography (CTC). MRCP has been widely used in the
clinic; however, it has no therapeutic effect compared with
endoscopic retrograde cholangiopancreatography.
Therefore, diagnostic methods in clinical use should be
selected according to the patient.
In the diagnosis and differentiation of obstructive biliary
tract disease, MRCP can display the shape of the obstruction
site because of the correlation between the shape of the
obstructive end and the nature of the lesion. Dependent on
the obstruction level and the displayed features, combined
with conventional plain and enhanced scans; obstructions
caused by calculous, congenital, neoplastic, and inammatory factors may achieve diagnostic and differential diagnosis (Vergel et al. 2006). Because of its safety and
non- invasiveness, MRCP, is one of the most effective modalities for imaging biliary obstruction, providing a reliable
basis for the diagnosis and treatment of biliary obstruction
and postoperative surgical evaluation (Fig.2.17).
2.3.3 Application ofMRI inBiliary Surgery
For biliary stones and inammatory lesions, MRCP
(Fig. 2.16) is a non-radiative and non-invasive imaging
technique not requiring contrast agents. Through MRCP,
the biliary tract system can be observed from multiple
angles; location and size of biliary stones can be displayed;
moreover, so-density or low-density stones that cannot be
displayed on CT can be shown as well. Abnormities in the
structure of the biliary tract can be clearly demonstrated.
Patients who underwent biliary tract surgery or received
cholangiopancreatographic examination with intubation
failure can be well evaluated. The use of MRCP in combination with T1 weighted image (T1WI) can signicantly
increase the detection rate for small common bile duct
stones. However, the examination of choledocholithiasis by
Fig. 2.17 Patient with cholangiocarcinoma, the common bile duct is
transected, and the intrahepatic bile duct is visibly dilated
30
S. Zheng et al.
References
Andrew W.Chapter 1:The principles of magnetic resonance, and asso-
ciated hardware. In: Magnetic resonance technology: hardware and
system component design, pp.1–47; 2016.
Flohr T, Ohnesorge B.Image visualization and post-processing tech-
niques. In: Multi-slice and dual-source CT in cardiac imaging.
Berlin: Springer; 2007.
Goldman LW. Principles of CT: multislice CT.J Nucl Med Technol.
2008;36(2):57–68.
Grover VPB, etal. Magnetic resonance imaging: principles and tech-
niques: lessons for clinicians. J Clin Exp Hepatol. 2015;5(3):246–55.
Miller CG, Joel K, Schwartz Lawrence H, editors. Medical imaging in
clinical trials. London: Springer; 2014. p.10–2.
Nitz W.Principles of magnetic resonance imaging and magnetic reso-
nance angiography. In: Reimer P, Parizel PM, Stichnoth FA, editors.
Clinical MR imaging. Berlin: Springer; 2006.
Vergel YB, Chilcott J, Kaltenthaler E, etal. Economic evaluation of
MR cholangiopancreatography compared to diagnostic ERCP for
the investigation of biliary tree obstruction. Int J Surg. 2006;4:12–9.
Imaging ofCommon Biliary
Tract Diseases
XianyueQuan, ShupingQian, ZhendongQi,
JingjingHuang, LiyingHan, andChihuaFang
3
3.1 Introduction
Both CT and MR imaging can be crucial for the nal diagnosis
of most biliary diseases, with both modalities allowing localization diagnosis, qualitative diagnosis, and detailed evaluation
of the biliary tract (Yeh etal. 2009). Three- dimensional reconstruction represented by CT and MRI plays a signicant role in
guiding precision surgery, providing important information for
tumor inltration characteristics, adjacent important vascular
structures, variations, and quantitative evaluation. This chapter
focuses on the imaging features of these two examination techniques in the diagnosis of biliary system diseases.
3.2 Congenital Biliary Diseases
3.2.1 Congenital Extrahepatic Biliary Atresia
Congenital Extrahepatic Biliary Atresia (EHBA) is characterized by obliteration or discontinuity of the extrahepatic
biliary tract, which is not accompanied by stones or tumors
(Perlmutter and Shepherd 2002).
3.2.1.1 CT Features
CT can clearly show the size of the gallbladder, the structure
of the porta hepatis, and the signs of secondary portal hypertension. Absence of the gallbladder or small gallbladder has
important diagnostic signicance (gallbladder width <4mm
and gallbladder length <15mm without meal stimulation). It
is caused by biliary atresia, gallbladder agenesis, decreased
synthesis of bile acids, and disappearance or emptying of the
cystic lumen (Hartley et al. 2009). Triangular high-signal
intensity in the hilar is considered to be caused by dilated
biliary ducts in the connective tissue. The perivascular space
of the portal vein and its branches are enlarged, and a slightly
X. Quan · S. Qian · Z. Qi · J. Huang · L. Han · C. Fang (*)
Zhujiang Hospital, Southern Medical University,
Guangzhou, China
low-density blur is observable on both sides of the portal
branches. “Bilateral signs” or “target signs” appear, indicating atresia of the common bile duct, edema around the hilar
of the liver, inammatory cell inltration, and brosis.
3.2.1.2 MRI Features
Similar to the manifestation of CT, MRI can reveal hepatosplenomegaly, cirrhosis, and nonspecic presentation of portal hypertension. Specically, MRI displays (Mitchell and
Alam 1999):
• Absent or small gallbladder in the porta hepatis. It should
be noted that the gallbladder can be enlarged if biliary
atresia occurs at the level below the opening of the
gallbladder.
• Lamellar or triangular thickening hyperintense signal
area around the portal vein and its branches in the porta
hepatis. This manifestation represents the residual dilated
bile duct structure within the brous connective tissue in
the hilum area; it has diagnostic signicance.
Conventional MRI cannot display conditions of the entire
intrahepatic and extrahepatic bile ducts. MRCP is a noninvasive technique for imaging the biliary tree visually and multidimensionally. On thin-section MRCP images, if the
extrahepatic biliary tree is not observed or discontinuous,
EHBA can be diagnosed combined with an absent or small
gallbladder and/or triangular hyperintense signal area in the
porta hepatis (Fig.3.1).
However, MRCP requires the content of water molecules
in the biliary tract to reach a certain volume for clear imaging, so it is affected by bile secretion. MRCP has the following disadvantages:
• The quality of MRCP images is susceptible to interfer-
ence of intestinal uid.
• Thin bile duct, a limited spatial resolution of MRCP, long
imaging time and high noise. Insufcient bile secretion or
a small gallbladder is easily misdiagnosed as EHBA.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
C. Fang, W. Y. Lau (eds.), Biliary Tract Surgery, https://doi.org/10.1007/978-981-33-6769-2_3
31
32
ab
cd
X. Quan et al.
Fig. 3.1 MRI manifestation of congenital extrahepatic biliary atresia.
(a, b) A T2WI in transverse and coronal planes, high vesicle-like signals in the hepatic portal area of T2WI, indicating changes in the small
gallbladder; (c) Patchy long T2 signal is seen in the hepatic portal area
3.2.2 Biliary Dilatation
and the periportal zone, indicating brosis changes, which can be
enhanced by enhanced scan; (d) The extrahepatic bile duct on MRCP is
not shown, and the intrahepatic bile duct is discontinuous
Type I
Most common, choledochal cyst or fusiform dilatation of
3.2.2.1 Todani Classication
Todani etal. (2003) dened biliary dilatation into ve major
types and several subtypes.
the common bile duct, accounting for 80%–90% of all bile
duct cysts (Fig.3.2). It is a benign dilatation that occurs in
any part of the intrahepatic or extrahepatic bile duct except