Urologic Ultrasonography

BASIC PRINCIPLES OF UROLOGIC
ULTRASONOGRAPHY
Eko Indra P

PHYSICAL PRINCIPLES
• Interaction of soundwaves
w/ tissues and structures
within the human body 
ultrasound imaging
• The soundwaves are
longitudinal waves  the
particle motion is in the
same direction as the
propagation of the wave
• The transducer = a
receiver for the returning
sound wave reconverting
the mechanical wave to
electrical energy

RESOLUTION
• Refers to the ability to
discriminate two objects in close
proximity to one another.
• Axial resolution: the ability to
identify as separate two objects
in the direction of the traveling
sound wave – directly dependent
on the frequency of sound waves
• Lateral resolution : the ability to
identify separately objects that
are equidistant from the
transducer  The shape of the ultrasound beam is simulated in
this drawing (purple). The focal zone (A) is located
to produce the best lateral resolution of the
medial renal cortex. The location of the focal zone
is designated by the caret (B). The location of the
focal zone can be adjusted by the operator.

MECHANISMS OF ATTENUATION
• Mechanisms of
attenuation include
reflection, scattering,
interference, and
absorption.
• Reflection occurs
when ultrasound
waves strike an
object, a surface, or a
boundary (called an
interface) between
unlike tissues

MECHANISMS OF ATTENUATION
• The amount of energy reflected
from an interface is also influenced
by the impedance of the two tissues
at the interface
• Scattering occurs when sound waves
strike a small or irregular object
• Pattern of interference is partially
responsible for the echo
architecture or texture of organs.
• Absorption occurs when the
mechanical energy of the ultrasound
waves is converted to heat
Relationship between
frequency and tissue
penetration

ARTIFACTS
• A misrepresentation
produced by the
interaction of
ultrasound waves with
tissues
• Example: acoustical
shadow, increased
through-transmission,
edging artifact, and
reverberation artifact
Increased through-
transmission
Edging artifact

MODES OF ULTRASONOGRAPHY
• Gray-scale Ultrasonography: 2D
• Doppler Ultrasonography: allows for the
characterization of motion, most commonly
blood flow, but it may also useful for detecting
the flow of urine
• Harmonic Scanning: produce an image with less
artifact and greater resolution
• Spatial Compounding: reduces the amount of
artifact and noise, producing a scan of better
clarity.

MODES OF ULTRASONOGRAPHY
• Sonoelastography: an evolving ultrasound
modality that adds the ability to evaluate the
elasticity (compressibility and displacement)
of biologic tissues
• Three-Dimensional Scanning: allow the
recognition of some tissue patterns that
would otherwise be unapparent on two-
dimensional scanning

DOCUMENTATION AND IMAGE
STORAGE
• Report: should include specific
info, must be signed by the
physician, and the indications
should be displayed at the top
of the report
• By convention, the liver is
used as a benchmark for
echogenicity
• Images: should include clear
image orientation
• By convention, structures
imaged by USG should be
oriented

PATIENT SAFETY
• Biologic effects: mechanical and thermal effect
• Mechanical effect  cavitation (may cause tissue
damage in certain circumstances)  mechanical
index (MI)
• Thermal effect : result of tissue heating 
thermal index (TI)
• MI and TI estimate the potential for biologic
effects of USG based on the mode, frequency,
power output, and the time of insonation
• These indices are not safety limits

RENAL ULTRASONOGRAPHY
• Transducer used is a curved array of 3.5 – 5.0
MHz. Pediatric may use a higher frequency
• Patient in supine position
• Visualization of the left kidney often requires
the patient to be turned into a lateral
position.
• Applications: percutaneous renal biopsy
• Limitations: Renal ultrasonography has poor
sensitivity for renal masses less than 2 cm

TECHNIQUES: RIGHT KIDNEY
• Scanning of the right kidney is performed with the
patient supine.
• The kidney is located by beginning in the midclavicular
line in the right upper quadrant.
• The transducer is moved laterally until the midsagittal
plane of the kidney is imaged.
From: Campbell-Walsh Urology 10th Edition

TECHNIQUES: RIGHT KIDNEY
• The probe is rotated 90 degrees counterclockwise.
• The midtransverse plane will demonstrate the renal
hilum containing the renal vein.
• The kidney is scanned from upper pole to lower pole.

TECHNIQUES: LEFT KIDNEY
• For left renal ultrasonography is identical to that of
the right side, but the left kidney is slightly more
cephalad than the right kidney.
• Bowel gas is more problematic on the left because
of the position of the splenic flexure of the colon.
• Visualization of the left kidney often requires the
patient to be turned into a lateral position.

NORMAL FINDINGS
• It is helpful to understand its anatomic
position within the retroperitoneum.
• This assists identifying the midsagittal
plane, which serves as a reference point
for a complete examination

KIDNEY ULTRASONOGRAPHIC
ANATOMY
Liver
Kidney

The lower pole of the kidney is displaced 15 degrees laterally compared with the upper pole (A).
The kidney is rotated 30 degrees posterior to the true coronal plane (B). The lower pole of the
kidney is slightly anterior compared with the upper pole.

NORMAL FINDINGS
• The adult right kidney is usually hypoechoic with
respect to the liver.
• The central band of echoes in the kidney  a
hyperechoic area that contains the renal hilar
adipose tissue, blood vessels, and collecting
system.
• Acoustic shadowing from ribs  move the probe to
a more lateral position or into the intercostal space.
• Taking a deep breath  the kidney can be moved
inferiorly to assist complete imaging

Midsagittal plane of the kidney. Note the relative hypoechogenicity of the renal pyramids (P)
compared with the cortex (C). The central band of echoes (B) is hyperechoic compared with the
cortex. The midsagittal plane will have the greatest length measurement pole to pole. A perfectly
sagittal plane will result in a horizontal long axis of the kidney.

NORMAL FINDINGS:
ECHOGENICITY
• The echogenicity of the kidney varies with age.
• Infant renal cortex  more hyperechoic, smaller
and less apparent central band of echoes
• Adult renal cortex  more hypoechoic with
respect to the liver (Emamian et al, 1993a).
• Chronic medical renal diseases  renal cortex
is often thinned and isoechoic or hyperechoic
with respect to the liver (O’Neill, 2001)

NORMAL FINDINGS: RENAL
SIZE
• Renal size changes over the lifetime of an individual.
• These are based on age, height, and weight of the
patient.
• Adult kidney  10 to 12 cm in length, 4 to 5 cm in
width.
• Measurements of renal volume may be appropriate
in cases of severe renal impairment.
• Renal measurements should be obtained in the
midsagittal plane and midtransverse plane.

RENAL SIZE (CONT’D)
• The thickness of the parenchyma  the average
distance between the renal capsule and the
central band of echoes.
• Subjective  the midlateral renal parenchyma in
the sagittal view is a common choice.
• No universal standard
– The renal cortical thickness  greater than 7 mm (Roger et al,
1994),
– The renal parenchymal thickness  greater than 15 mm
(Emamian et al, 1993b).

The distinction between renal cortical thickness and renal parenchymal thickness is that the renal
parenchyma is measured from the central band of echoes to the renal capsule. The renal cortex is
measured from the outer margin of the medullary pyramid to the renal capsule.

TRANSABDOMINAL PELVIC
ULTRASONOGRAPHY
• Transducer used is a curved array of 3.5 – 5.0
MHz.
• Commonly performed with the patient supine
and the sonographer on the patient’s right side
• Bladder may also be assessed using transvaginal
and transrectal approaches.
• Applications: Transabdominal US-guided
percutaneous bladder aspiration
• Limitation: Yields limited information in patients
with an empty bladder

ULTRASONOGRAPHY OF THE
SCROTUM
• High-frequency transducers,
generally in the range of 7 to 18
MHz, may be employed.
• Patient should be supine with the
scrotum supported on a towel or on
the anterior thighs.
• Applications: percutaneous
testicular sperm aspiration,
percutaneous epididymal sperm
aspiration
• Limitations: Caution should be used
when interpreting Doppler flow
studies in the evaluation of
suspected testicular torsion

ULTRASONOGRAPHY OF THE PENIS
AND MALE URETHRA
• Best performed with a 12- to 18-MHz linear array transducer
• The more proximal aspects of the urethra and corpora cavernosa
are best assessed through a perineal approach
• Transperineal and translabial ultrasonography has also been
used for evaluation of the pelvic floor for both diagnostic
purposes and postprocedural follow-up
• Applications: evaluation of erectile dysfunction and penile
curvature
• Limitations: The complete evaluation requires a dorsal or ventral
interrogation of the exposed phallus and a perineal approach
and the evaluation of erectile dysfunction requires qualitative
and quantitative measurements of blood flow in the penile
arteries

TRANSRECTAL ULTRASONOGRAPHY
OF THE PROSTATE
• A high-frequency 7.5 - 10-MHz
transducer is usually used. This
can be a biplanar or singleplane
transducer
• It is essential to perform a digital
rectal examination before
inserting the ultrasound probe
• Applications: TRUS-guided biopy
• Limitations: Bowel preparation
is sometimes necessary for
imaging.

Urologic Ultrasonography

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