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80
Y. J. El-Abd and K. D. Hagspiel
a
Subclavian vein
Axillary vein
Brachial vein
Cephalic vein
Basilic vein
Median antebrachial
vein
Radial vein
Median cubital
vein
Ulnar vein
Azygos vein
Hemi-azygos vein
b
Fig. 6.12 Veins of the upper extremity Venous anatomy:drainage, of extremities. (a) Artist illustration. (b) MRV of the upper extremity
paired veins for every artery. This unique feature is useful
when attempting to identify these veins on ultrasound, as
the paired veins often produce a “mickey mouse ears”
appearance of the artery centrally accompanied by two
veins. In addition the veins are easily compressible on
sonography while the artery is not. The brachial veins then
merge to form the axillary vein and eventually the subclavian vein.
Peroneal (fibular)
ab
6 The IR Road Map: Vascular Anatomy Overview
Common iliac vein
External iliac vein
Internal iliac vein
Common femoral vein
Profunda (deep)
femoris vein
Superficial femoral
vein
Greater saphenous
vein (superficial)
81
Lesser (small)
saphenous vein
(superficial)
veins
Fig. 6.13 Veins of the lower extremity. (a) Artist illustration. (b) MRV of the lower extremity
Popliteal veinPopliteal vein
Anterior tibial
veins
Posterior tibial
veins
Similar to the upper extremity, the venous drainage of the
lower extremity consists of a supercial and deep venous
system (Fig.6.13). The supercial veins include the lesser
and greater saphenous veins. The lesser saphenous vein
starts laterally but then courses posteriorly and empties into
the popliteal vein. The greater saphenous vein is a long vein
that courses medially almost the entire length of the lower
extremity before it nally empties into the common femoral
vein. The deep venous structures parallel the arterial system.
The calf veins, consisting of the anterior tibial, posterior
tibial, and peroneal veins, are duplicated. These eventually
empty into the popliteal vein, which is normally singular but
lows the course of the artery and becomes the femoral vein in
the adductor canal. In the groin near the hip, the deep femoral vein joins the femoral vein and from there on forms the
common femoral vein. The common femoral vein accepts
the greater saphenous vein anteriorly as already described
and then crosses the inguinal ligament as the external iliac
vein, merging with the internal iliac vein into the common
iliac vein. The left common iliac vein can be narrowed due to
extrinsic compression by the right common iliac artery against
the lumbar spine, a condition referred to as May- Thurner
syndrome. The bilateral common iliac veins join to form the
inferior vena cava (IVC).
can be duplicated in some patients. The popliteal vein fol-
Introduction toCross-Sectional Imaging
AdamDonithan, JessieJahjah, andPatrickT.Norton
Introduction
Diagnostic radiology is the foundation upon which interventional radiology is built; a thorough understanding of DR is
crucial to not just be procient in but excel in IR.Crosssectional imaging provides the three-dimensional roadmap
between anatomic structures that must be envisioned when
performing procedures using two-dimensional image guidance. Interventionalists need to be familiar with the acquisition techniques and inherent limitations of imaging. An
understanding of ultrasound, computed tomography (CT),
and magnetic resonance imaging (MRI) is needed to choose
what modalities will be best suited to dene anatomy and
pathology as well as guide procedures.
Imaging Modalities
Ultrasound
7
trading off penetration (lower frequency) and resolution (higher
frequency). When sound waves encounter different tissue, they
can be reected, scattered, refracted, or absorbed. Ultrasound
images are created from reected sound returning from tissue.
Sound pulses are sent from the transducer, interact with the
underlying tissues, and are then detected by the same transducer. An array of crystals detect the returning sound, and this is
used to create a two-dimensional image. Individual pixel brightness in the image is calculated based on the returning sound
intensity. Pixel location (depth) is calculated by the time lapse
between sending the pulse and receiving the echo.
Key Point
• Lower-frequency probes have greater penetration
and lower spatial resolution (commonly a curved
array probe).
• Higher-frequency probes have less penetration and
higher spatial resolution (commonly a linear array
probe).
Ultrasound images are created using sound waves reected from
tissues with different acoustic impedances. Advantages of ultrasound are lack of ionizing radiation, real-time imaging, portability, and low cost. Using Doppler techniques, qualitative and
quantitative characteristics of blood ow can be determined. In
addition to its diagnostic utility, ultrasound is useful for interventional procedures including gaining access (e.g., vascular, biliary, renal), performing biopsies, and guiding ablative therapies.
Sound travels in the form of waves that compress (increases
density) and stretch (decreases density) the conducting medium,
be it gas, liquid, or solid. While audible sound waves detected
by the human ear have a frequency range from 20Hz to 20kHz,
the sound waves used in ultrasound imaging range from 1 to
15MHz. Different transducers have different frequency ranges,
A. Donithan · J. Jahjah · P. T. Norton (*)
University of Virginia Health System, Department of Radiology
and Medical Imaging, Charlottesville, VA, USA
e-mail: ard8g@virginia.edu; jj3ta@virginia.edu; ptn7y@virginia.edu
© Springer International Publishing AG, part of Springer Nature 2018
N. A. Keefe et al. (eds.), IR Playbook, https://doi.org/10.1007/978-3-319-71300-7_7
Objects in an ultrasound image are described by their
relative echogenicity to surrounding structures. Anechoic
refers to a lack of echoes and appears as black on the image.
Hypoechoic structures have fewer echoes and are darker on
the image compared to surrounding tissues. Isoechoic means
equal to the surrounding tissues. Hyperechoic, or echogenic,
describes structures with the greatest number of echoes and
appears brighter than surrounding tissues.
Using Doppler techniques, one can characterize blood ow
within a vessel. This is either displayed as color velocity maps
over grayscale images or a graph of the blood velocity versus
time at a selected location in the blood vessel. This graph is
referred to as spectral imaging. These techniques take advantage of the Doppler effect, a phenomena in which sound waves
reected from a moving object results in a frequency shift.
A car horn changing pitch as it drives past an observer is a
real- world illustration of a Doppler shift. Thus, blood moving
83
84
A. Donithan et al.
toward the transducer reects sound waves at a higher frequency than the incident sound waves; blood moving away
from the transducer reects lower frequency sound waves.
The speed of the blood is proportional to the shift in frequency
and is calculated using the Doppler equation [1].
Computed Tomography
Computed tomography directs ionizing radiation in the form
of x-rays through the patient to create 3-D tomographic datasets. The components of a CT scanner include an x-ray generator (source), an arc-shaped detector that is housed on the
opposite sides of a donut-shaped gantry, and a movable table
that slides through the gantry. Current multi-detector CT
(MDCT) scanners have multiple parallel rows of detectors to
increase speed and spatial resolution. The generator and
detectors spin around the patient allowing acquisition of data
from every angle through the patient. This occurs while the
patient is simultaneously moved through the center of the
gantry to collect information over the length of the body. The
scanner calculates the degree of reduction of photon energy
for each location in the body, collected from thousands of
angles, resulting in the creation of a 3-D image dataset.
The smallest imaging unit in each dataset is the voxel, a
cubic structure which has a length, width, and height, and is
assigned a CT number (Hounseld units, HU) based on the
attenuation of x-rays by the body. In modern scanners, voxels smaller than 1mm
HU is far greater than can be displayed on a monitor, windowing is used to select a range of HU to be viewed and
assign them a varying shade from black to white. There are
dedicated windows for viewing bones, soft tissues, vessels,
lungs, etc. Viewer applications allow the user to view the CT
data in any 2-D plane or reconstruct 3-D volume rendered
images from the data. Advanced tools are used for following
a vessel along its centerline and automating measurements of
vessel diameter and length [2].
Iodinated contrast agents are administered during the examination to increase the conspicuity of the vasculature and internal
architecture of organs. These contrast agents are contraindicated
in patients with severe chronic kidney disease (glomerular ltration rates <30 mL/min/1.73 m2) that are not yet on dialysis.
However, these agents may be used in dialysis patients, as they
can be ltered from the blood. Patients with a history of mild
allergic reactions to iodinated contrast agents should be medicated with steroids and diphenhydramine prior to administration; these agents should be avoided in patients with a history of
severe reactions (see Chap. 5 for more information).
Key Point
Iodinated contrast agents are contraindicated in patients
with GFR <30 not on dialysis. They can be used in dialy-
sis patients as they can be ltered from the blood.
3
can be obtained. Since the range of
CT is advantageous for applications that require high
spatial resolution (angiography) and rapid imaging (trauma
and unstable patients). It is also useful for guiding procedures,
such as placing a biopsy needle into a mass. The downside of
CT is that it requires ionizing radiation and often the use of
nephrotoxic contrast agents, both increasing risk to the
patient and operator alike.
Magnetic Resonance Imaging
MRI is a technique by which hydrogen nuclei within tissues are excited with electromagnetic elds, releasing
radiofrequency waves that are converted into images. The
advantages of this technique include lack of ionizing radiation, excellent soft tissue differentiation allowing sensitive identication of pathology, and excellent angiographic
imaging. The disadvantages include increased imaging
time and relative expense as compared to the other imaging modalities. Additionally, imaging-guided procedure is
more difcult using MRI as compared to CT because
access to the patient is limited due to the long length of
the tube. MRI uses a very strong magnet, thousands of
times stronger than the earth’s magnetic eld, which creates problems for patients with metallic implants and also
means nothing magnetic can be brought in with the
patient, for risk of it becoming a projectile, making monitoring a patient complicated.
Image acquisition in MRI is controlled by pulse
sequences that are designed to accentuate different tissue
properties. T1 and T2 characteristics are intrinsic properties
of tissue and are based on the changes in proton spin (relaxation properties) in the longitudinal or transverse direction,
respectively. T1-weighted imaging is often used for delineating anatomic structures and when using gadolinium contrast agents, such as with MR angiography (MRA). These
sequences are identied by low, or dark, signal of simple
uids like the cerebral spinal uid (CSF). T2-weighted
imaging is useful for identifying pathologic processes (associated with edema) or cystic structures, as structures with
high water content appear bright (high in signal) as compared to surrounding structures [3].
Gadolinium-chelated contrast agents, where gadolinium
is bound to a carrier molecule, are the most common type of
agent used for MRI.This class of agents increases signal on
T1-weighted imaging, making blood appear bright, which is
useful for angiography and enhancing structures with high
blood volume. Gadolinium contrast agents should not be
used in patients with severe renal insufciency or on dialysis
due to the risk of nephrogenic systemic sclerosis (NSF).
Unlike iodinated x-ray contrast, gadolinium agents are not
safely ltered by dialysis. Additionally, recent studies have
suggested that elemental gadolinium can become unbound
from its carrier molecule and deposit in tissues including
brain and bones. However, the consequence of this deposition
7 Introduction toCross-Sectional Imaging
85
is still unclear. Both NSF and gadolinium deposition appear
to be more likely with agents of linear molecular structure as
compared to those with cyclic structures [4].
Key Point
Nephrogenic systemic brosis (NSF) is characterized
by erythematous and indurated plaques on the skin.
Gadolinium should be avoided in patients with eGFR
<30mL/min.
Imaging Planes andOrientation
The conventional cross-sectional imaging planes include
axial (transverse), coronal, and sagittal. These standard orientations for displaying medical images are necessary for rapid
identication of anatomy. The axial plane (Fig.7.1a) is perpendicular to the long axis (superior-inferior) of the patient.
For CT and MRI, this plane is orientated as if looking upward
from the feet of a patient lying supine in a bed. The left side
of the image displays the anatomic right side, and anterior is
directed toward the top of the image. The coronal imaging
plane (see Fig.7.1b) is perpendicular to the anterior-posterior
axis and is oriented as if the viewer is facing the patient: the
left side of the image displays the anatomic right side, and
superior is directed toward the top of the image. Sagittal
imaging plane (see Fig.7.1c) is perpendicular to the left-right
axis with anterior directed toward the left side of the image
and superior directed toward the top.
Orientation is slightly different for ultrasound, as the transducer is most often located at the top of the image and deep
structures located toward the bottom of the image. Ultrasound
images are acquired such that the transducer is placed with the
right-sided anatomy on the left of the transverse image and
superior anatomy on the left of a sagittal or coronal image.
Cross-Sectional Anatomy
Chest
Segmental Lung Anatomy
The right lung is divided into three lobes: upper, middle, and
lower. The right upper lobe is divided into three segments:
apical, anterior, and posterior. The middle lobe is divided
into two segments: medial and lateral. The right lower lobe is
divided into ve segments: superior, anterior basal, medial
basal, lateral basal, and posterior basal.
The left lung is divided into two main lobes: upper and
lower. The upper lobe contains the upper portion and the
lingula. The upper portion is divided into two segments: anterior and apicoposterior. The lingula is divided into two segments: superior and inferior. The left lower lobe is divided
into four segments: superior, anteromedial basal, lateral basal,
and posterior basal (Fig.7.2).
Mediastinum
The superior mediastinum is the plane above the aortic arch
which contains the thoracic inlet structures. The anterior
mediastinum contains the thymus, lymph nodes, and mesenchymal tissue. The middle mediastinum contains the heart,
major vessels, bronchi, lymph nodes, and phrenic nerve. The
posterior mediastinum is located between the anterior margin of the vertebral bodies and the pericardium, containing
the descending aorta, esophagus, thoracic duct, lymph nodes,
nerves, and paravertebral areas (Fig.7.3).
Fig. 7.1 Imaging planes. (a) Axial (or transverse) plane from a CT of
the abdomen. Perspective is that of a patient lying supine with feet coming out of the image. (b) Coronal plane from a CT of the abdomen and
pelvis. Perspective is that of the patient facing the viewer. (c) Sagittal
midline plane from a CT of the abdomen and pelvis. The prospective is
from the side of the patient facing image left
86
Fig. 7.2 Segmental anatomy
of the lung. Axial imaging
from CT of the chest with
analogous pulmonary
segments of each lung colored
similarly. (a) Level of lung
apices. (b) Level of the main
pulmonary artery. (c) Level of
the body of the left atrium.
(d) Level of the lower lobes
of the lung
A. Donithan et al.
7 Introduction toCross-Sectional Imaging
Fig. 7.3 Thoracic cross-
sectional anatomy. Axial CT
images in mediastinal
windows at the following
levels: (a) supra-aortic
vessels, (b) carina, (c)
ascending aorta, and (d) left
atrium
87
88
A. Donithan et al.
Pulmonary Arteries
The main pulmonary artery courses posteriorly and superiorly from the pulmonic valve. It divides into the left and right
pulmonary arteries at the level of the fth thoracic vertebral
body. The right pulmonary artery is longer than the left one,
coursing rightward through the mediastinum. The left pulmonary artery is directed in a more posterior course.
Segmental and subsegmental pulmonary arteries parallel
segmental and subsegmental bronchi and run adjacent to
them (see Fig.7.3).
Pulmonary Veins
There are typically four pulmonary veins entering the left
atrium, two draining each lung. The right superior pulmonary
vein typically drains the right upper and middle lobes; the right
inferior pulmonary vein drains the right lower lobe. The left
superior pulmonary vein drains the left upper lobe, and the left
inferior pulmonary vein drains the left lower lobe. The pulmonary veins arise in the interlobular septa and as such do not
course adjacent to the bronchi (see Fig.7.3).
Bronchial Arteries
The bronchial arteries typically arise from the thoracic aorta
at the T3 to T8 levels and also supply the bronchi, vagus
nerve, posterior mediastinum, and esophagus. There are usually two left bronchial arteries that arise from the anterior
surface of the thoracic aorta. The superior left bronchial
artery is posterior to the left main bronchus, and the inferior
left bronchial artery is inferior to the left main bronchus. The
right bronchial artery typically arises from the right posterolateral aspect of the thoracic aorta and typically has a common origin with an intercostal artery (intercostobronchial
trunk). The bronchial arteries are said to have an orthotopic
origin if they arise from the proximal descending aorta and
an ectopic origin if they arise from the inferior aortic arch,
distal descending aorta, innominate artery, subclavian artery,
or internal thoracic artery.
Thyroid andParathyroid
The thyroid gland is composed of two lobes, right and left,
connected by an isthmus (Fig.7.4). Each lobe has a superior
and inferior pole. The superior pole is rounded, and the inferior pole is elongated. The thyroid extends from C5 to T1,
anterior to the thyroid and cricoid cartilages. Each lobe measures 4–6cm in length and less than 2cm in depth. The normal thyroid parenchyma appears homogenous on ultrasound.
The parathyroid gland lies posteromedially to the thyroid
gland and is infrequently identied on imaging unless it is
abnormal. A nodule within a thyroid gland is dened as a
region within the thyroid that appears sonographically distinct from the thyroid while being conned by the thyroid
parenchyma and capsule.
Thyroid ultrasound is performed, while the patient lies
supine with the neck hyperextended. A high-frequency transducer (7.5–15MHz) can be used to produce high-resolution
images due to the supercial location of the gland. Transverse
imaging is used to locate thyroid nodules and helps in
identifying their relationship to surrounding structures.
Longitudinal imaging, where more of the gland is present on
a single image, helps to evaluate internal architecture, vascularity, and extra-thyroid extension. Both transverse and longitudinal imaging help to differentiate a thyroid nodule from
a parathyroid adenoma.
Abdomen andPelvis
A thorough understanding of the location of the organs within
the abdomen and pelvis is necessary for planning interventional procedures, for assessing results of interventions, and for
detecting complications. The liver is located within the right
upper quadrant; the majority is covered by peritoneum, making
it predominantly an intraperitoneal organ. The spleen is similar
but located within the left upper quadrant. The stomach is
located in the epigastrium (middle upper abdomen) and is
within the peritoneal cavity. The cecum, transverse colon, and
sigmoid colon are peritoneal, while the ascending and descend-
Fig. 7.4 Thyroid ultrasound. (a) Transverse plane of the thyroid gland
using a high-frequency transducer demonstrates a normal homogenous
thyroid gland. (b) Longitudinal plane of the thyroid gland using a high-
frequency transducer demonstrates homogenous thyroid architecture
with a rounded superior pole and an elongated inferior pole. A welldened hypoechoic cyst is visualized in the superior pole
7 Introduction toCross-Sectional Imaging
89
ing colon are retroperitoneal. The small bowel is within the
peritoneal cavity. The bowel’s location should be considered
whenever an anterior procedural approach is used. The kidneys
and ureters are retroperitoneal organs that are located posteriorly and lateral to the lumbar spine. The uterus is deep within
the pelvis and located within the peritoneal cavity. The urinary
bladder is within the anterior pelvis, with only the dome
exposed to the peritoneal cavity (Figs.7.5, 7.6, and 7.7).
Liver
The liver is located predominantly in the right upper quadrant
of the abdomen and is bound by the diaphragm superiorly,
anteriorly, and partially posteriorly. It is in contact with the
peritoneum except for the superior-posteriorly located bare
area, where it is in direct contact with the diaphragm. Thus,
most extracapsular hemorrhage from the liver will extend
into the peritoneal cavity. Due to the close proximity of the
liver to the diaphragm, there is signicant movement of the
liver relative to the skin surface with respiration, making
control of respiratory excursion an important part of hepatic
procedures.
The liver is functionally divided into eight segments each
with a separate central portal venous and hepatic arterial supply, biliary drainage, and hepatic venous drainage. These
segments were made famous by the French surgeon Couinaud
and are used during hepatic resection and transplantation.
Fig. 7.5 Axial CT of the abdomen and pelvis of a male, (a–f) superior to
inferior. (a, b) The liver occupies the right upper quadrant, and the stomach and spleen occupy the left upper quadrant. The aorta is located anterior
and slightly to the left of the vertebral column, behind the crus of the diaphragm. (c) The most superior visceral branch of the aorta is the celiac
artery, which supplies the spleen, liver, pancreas, stomach, and duodenum.
The pancreas is in the retroperitoneal epigastrium and is anterior to the
splenic vein. (d) The second visceral branch of the abdominal aorta is the
superior mesenteric artery (SMA), which supplies the jejunum, ileum, and
ascending and transverse colon. The SMA is located posterior to the superior mesenteric vein (SMV) proximally and rotates left of the SMV distally. The kidneys are easily discerned at this level. The left renal vein
courses between the aorta and the SMA, to drain into the IVC.The renal
arteries’ origins are just inferior to this level. (e) Level of the right renal
hilum, where the arteries, veins, and ureters enter and exit the kidney. The
duodenum crosses the midline at this level, between the aorta and SMA.
(f) The inferior mesenteric artery (IMA) is the inferior most visceral artery
branch from the abdominal aorta, supplying the colon from the splenic
exure to the upper two thirds of the rectum. The bodies of the psoas
muscles are just lateral to the lumbar spine at this level. (g) Level just
inferior to the aortic bifurcation and common iliac vein conuence. Note
that the left common iliac vein (CIV) courses between the right common
iliac artery (CIA) and the spine, a potential area where it can become compressed. (h) At the level of the urinary bladder, the common iliac vessels
are separated into the internal branch deep in the posterior pelvis and the
external branch located anteriorly. The external pelvic musculature including the gluteal muscles are present at this level and would be traversed
when a posterior approach for pelvic abscess drainage is used
90
A. Donithan et al.
Fig. 7.5 (continued)