Download SMU-DDE-Assignments-Scheme of Evaluation PROGRAM Bachelor

SMU-DDE-Assignments-Scheme of Evaluation
PROGRAM
SEMESTER
SUBJECT CODE &
NAME
BK ID
DRIVE
MARKS
Q.
No
1.
A
Bachelor in Medical Imaging Technology
V
BMI 502– Computed Tomography Imaging and Patient Care
B2082
WINTER 2015
60
Criteria
Marks
Total
Marks
Explain the technical factors of CT brain perfusion scans.







The most common technique associated with CT perfusion
scanning is based on the first pass of a contrast bolus through
the brain tissue. With this technique a 50-mL IV bolus of a
non-ionic low osmolality contrast is injected at 4 to 5 mL/s.
A helical scanner is used to produce a dynamic set of images
at a single location. A 5-second scan delay is used and slices
are typically 5 mm thick. Typical scan durations are in the
range of 40 to 45 seconds.
The slices are produced by repeatedly scanning the same
region at the same table position, a technique some
manufacturers refer to as the cine mode. Multislice scanners
allow several z position slices to be scanned simultaneously.
Scans are typically acquired at 5-mm sections to lessen beam
hardening artifacts, and then reformatted into 10-mm-thick
sections for viewing to improve the signal-to-noise ratio.
The brain perfusion protocol begins with an unenhanced scan
of the whole brain. Although the level for scanning the
enhanced portion of the study may be selected at the time of
examination based on the unenhanced CT findings, a
transverse slice through the level of the basal ganglia contains
territories supplied by the anterior, middle, and posterior
cerebral arteries, thus offering the opportunity to interrogate
each of the major vascular regions.
The outlined areas on the upper two rows of images are the
basal ganglia. A major limiting factor of older helical scanners
was the 10- to 20-mm maximum anatomic coverage. Often a
second bolus of contrast was necessary so that the patient
could be scanned at a different location, typically in a more
cephalad direction above the lateral ventricles.
The first step in post processing the acquired images using the
perfusion software is to select a reference artery and a
reference vein. The reference artery should be 1) seen in crosssection, 2) one of the first to enhance, 3) produce a curve with
a high enhancement peak, or 4) produce a curve with a narrow
width.
The most common choice of reference artery is the anterior
(Unit 2, Section 2.3)
10
10
SMU-DDE-Assignments-Scheme of Evaluation
2.
A
cerebral artery. The reference vein should be the largest
venous structure available or one that produces an
enhancement curve with the highest peak.
 The superior sagittal sinus is the vein most often used as the
reference. An ROI is placed on the reference artery and the
reference vein so that contrast-enhancement curves can be
generated. Analysis of the contrast enhancement curves guides
the selection of pre enhancement and post enhancement
images.
 The pre enhancement image is that last image before contrast
arrives. The post enhancement image is the point immediately
after the first pass of the contrast bolus when the timeattenuation graph begins to flatten. The perfusion software
then generates color-coded maps demonstrating:
a) Regional cerebral blood volume, or rCBV
b) Blood mean transit time, or MTT, through cerebral
capillaries
c) Regional cerebral blood flow or rCBR. Quantitative data
can be extracted from the maps by placing multiple ROIs
in the brain parenchyma.
d) Brain perfusion studies are frequently ordered with a
CTA of the circle of Willis or the carotid arteries. In these
situations the CTA should be performed first and the
brain perfusion study can immediately follow.
Discuss the general methods of thoracic scanning.
CT of the airways
 Technical parameters used for CT imaging of the airways
include the use of thin sections (1.25 mm or less), a fast
acquisition that allows the entire lungs to be scanned during a
single breath-hold, optimal spatial resolution, and the use of
post processing techniques. Overlapping z axis image
reconstruction of 50% is typical. Neither IV nor oral contrast
media are routinely required. IV contrast may be used in cases
of airway tumors.
 Airway imaging is routinely performed at both inspiration and
expiration. CT is generally accepted as the best imaging
technique for assessment of disease of the central airways and
is most commonly used to look for narrowing that may occur
in patients who have been intubated in the past.
 Applying post processing techniques, such as volume
rendering, may be referred to as CT bronchography. Virtual
bronchoscopy is accomplished with similar post processing
techniques, but is different in that it offers an internal
rendering of the tracheobronchial walls and lumen
High-resolution CT
 High-resolution CT (HRCT) is used to evaluate the lung
parenchyma in patients with known or suspected diffuse lung
diseases such as fibrous is and emphysema. Like airway
(Unit 3, Section 3.2)
5+5
10
SMU-DDE-Assignments-Scheme of Evaluation
3.
imaging, HRCT protocols use thin sections (1.5 mm or less), a
fast acquisition to reduce motion artifact, and optimal spatial
resolution. In addition to the thin sections, spatial resolution is
optimized by the selection of an edge-enhancing algorithm
(such as a bone algorithm) and a display field of view (DFOV)
that is just large enough to include the lungs.
 In some institutions, HRCT protocols are incremental,
meaning images are obtained with an interval of 10 mm or
more between slices and only approximately 10% of the lung
parenchyma is scanned. This technique is intended to provide
representative areas of lung disease. However, because
evidence of some types of diffuse lung disease may not be
uniform in distribution throughout the lung, this method of
sampling may result in characteristic foci of the disease not
being imaged.
 More recently, as MDCT scanners have become common
place, the technique known as volumetric HRCT is replacing
the HRCT axial protocols. Volumetric HRCT protocols use a
helical mode to acquire images of the entire lung, rather than
representative slices.
 Because these helical protocols cover the entire lung, they
result in a more complete assessment of the lung. Lung
nodules that could be missed between slices in incremental
protocols are not missed with volumetric HRCT, and the
central airways can be evaluated at the same time.
 In addition, they allow post processing techniques such as
maximum (MIP) and minimum (MinIP) intensity projection
reformation. Although there are clear advantages to the use of
volumetric HRCT over an interspaced technique, the increased
radiation exposure is a consideration. Many volumetric HRCT
protocols decrease the tube current (mA) to reduce the
radiation dose.
 Many HRCT protocols (both volumetric and axial) include
more than one series of scans. In all patients there is a gradual
increase in attenuation and vessel size from anterior to
posterior lung regions owing to the effect of gravity on blood
flow and gas volume.
 Therefore, HRCT protocols are routinely obtained at full
inspiration. However, expiratory images are useful in many
instances. For example, expiratory images better depict
bronchiolitis and air trapping.
Discuss cardiac CT technique.
(Unit 5, Section 5.2)
SMU-DDE-Assignments-Scheme of Evaluation
A
4.
A

General-purpose CT protocols can often be used in imaging of
abdominal, thoracic, and cerebral vessels in which image
quality is not substantially influenced by cardiac motion or
vessel pulsation. However, for studies of the heart and
coronary arteries, dedicated cardiac CT acquisition techniques
are needed to produce images free of motion artifact.
 Pharmacologic heart rate control: Essentially the CT
scanner is a fast camera, but as fast as state-of-the-art scanners
are, they cannot take a motion free picture when the heart is
beating too fast. Therefore, many institutions use β -blockers
as part of their cardiac CT protocols. β-blockers are used to
lower the heart rate to less than 65 to 70 beats per minute
(bpm) and to make the rhythm more regular.
 ECG gating: To minimize cardiac motion artifact, most
cardiac CT protocols use images acquired during the point of
the cardiac cycle with the least cardiac motion. Most often this
point is during end-diastole, but may also be at end-systole. In
other words, just before or just after the left ventricle is fully
contracted. However, different structures may be most still at
slightly different phases of the cardiac cycle.
 Contrast administration: Most cardiac CT protocols require
the intravenous administration of iodinated contrast agents.
Standard screening for contraindications to the contrast agent
(e.g., renal impairment, iodine allergy) is necessary. An
intravenous line is placed using a large-lumen (20-gauge or
larger) flexible cannula in a vein of sufficient diameter to
accommodate a relatively high injection rate.
 Breath-hold: It is very important that the patient suspend
respiration during scan acquisition. Breathing during the scan
will result in motion artifact. Careful breath-hold instructions
should be given to the patient before the scan begins. It is
often helpful to have the patient practice holding his or her
breath in moderate inspiration.
Discuss the imaging studies for acute appendicitis.



Many diseases other than acute appendicitis may produce
signs and symptoms indistinguishable from those of acute
appendicitis. In situations for which a clear diagnosis of
appendicitis cannot be made by the patient’s history,
physical examination, and laboratory evaluation, radiologic
testing particularly ultrasonography and CT can be useful.
Plain radiographs of the abdomen are frequently obtained as
part of the general evaluation of a patient with an acute
abdomen, but they are rarely helpful in diagnosing acute
appendicitis. Barium enema is unreliable in the diagnosis of
acute appendicitis and has been replaced by ultrasonography
and CT.
Ultrasonography is inexpensive and widely available, does
not require contrast agents, and poses no special risk to the
10
10
(Unit 8, Section 8.2)
10
10
SMU-DDE-Assignments-Scheme of Evaluation
5.
A
fetus in pregnant patients. It is particularly well suited for
evaluating right lower quadrant or pelvic pain in pediatric
and female patients. However, the technique used to
visualize the appendix, called graded compression
sonography, is highly operator dependent.
 Some of the difficulties with ultrasonography are related to
the fact that a normal appendix must be identified to rule out
acute appendicitis. This is difficult in obese or very
muscular patients or when there is an associated ileus that
produces shadowing secondary to overlying gas-filled loops
of bowel.
 Accuracy of ultrasound also decreases with retrocecal or
pelvic locations of the appendix. In addition, the following
scenarios can occur: a false-positive scan can occur in the
presence of periappendicitis from surrounding inflammation;
a dilated fallopian tube can be mistaken for an inflamed
appendix; or inspissated stool can mimic an appendicolith.
 Finally, patients often complain of discomfort resulting
from the transducer pressure during ultrasound evaluation.
Despite these limitations, when institutions are comfortable
with ultrasound for the evaluation of suspected appendicitis,
ultrasonography continues to serve as the primary imaging
study in children and in young or pregnant women. CT is
more accurate than ultrasonography.
 Also, because it is not as dependent on the skill and
experience of the operator, CT is more reproducible from
hospital to hospital. The diagnostic accuracy rate of CT for
acute appendicitis is reported to range between 93% and
98%.
 Findings on CT increased the certainty of diagnosis more
than findings on ultrasonography. Although ultrasonography
is recommended as the initial imaging study in children,
young women, and pregnant women, CT is most often
recommended as the initial study in all other patients.
 In addition, CT is recommended for patients in whom
sonographic evaluation is suboptimal or indeterminate, or for
those patients in whom perforation is suspected.
Explain the challenges in examination of shoulder and knee.
Shoulder
 Noncontrast CT is often requested for the evaluation of
bony trauma. Thin slices are acquired in the axial plane
beginning at the acromioclavicular joint and extending a
few centimeters below the most inferior fracture line
(determined by careful examination of the last few slices
or asking a radiologist for assistance).
 CT arthrography of the shoulder is useful for evaluation of
the joint capsule and intracapsular structures and for
finding loose bodies within the joint.
 CT arthrography can be performed either with a single or
(Unit 10, Section 10.3)
5
10
SMU-DDE-Assignments-Scheme of Evaluation
6.
A
double contrast technique (0.5 to 3.0 mL of iodinated
contrast material and approximately 10 mL of room air).
 Thin axial slices begin at just above the acromioclavicular
joint and end just below the glenoid fossa. For either
indication the patient is positioned supine on the CT table.
 The arm to be examined is downward alongside the body,
the opposite arm is extended over the patient’s head to
reduce the x-ray beam absorption as much as possible.
Knee
 Although MRI is the primary modality for the evaluation
of internal derangement of the knee, CT remains the
modality of choice in certain situations, such as tibial
plateau fractures.
 The primary indication of knee CT is to assess the degree
and alignment of fracture fragments, particularly at the
articular surfaces. Knee CT is also performed to assess the
integrity of the bone around prosthesis.
 The display field of view (DFOV) is focused on one knee
only and must include the patella, both femoral condyles,
and the proximal tibia through the fibular head. The patient
typically lies supine on the scanner table with legs
extended, knees side-by-side, and enters the scanner feet
first.
 CT of the knee is sometimes performed immediately after
an arthrogram of the knee in which iodinated contrast or air
has been injected directly into the joint space.
Explain FDG PET imaging.
Working of PET
 PET creates an image from the radiation given off when
positrons (i.e., antimatter electrons) encounter electrons in
the body. To do this, patients are given a
radiopharmaceutical with a short half-life, made up of a
radionuclide (in this case 18F) linked to a pharmaceutical
agent (deoxyglucose).
 The radionuclide emits positrons that encounter electrons
in the body. They annihilate each other, producing highenergy photons (i.e., annihilation photons) that can be
detected by the imaging device.
 The pharmaceutical portion of the radiopharmaceutical
(deoxyglucose) allows localization that favor glycolysis.
PET is unique because it creates images of the body’s
physiologic functions, such as blood flow and metabolism.
 PET uses unique radiopharmaceuticals different from those
used in traditional nuclear medicine.
 PET radiopharmaceuticals can be labeled with isotopes that
are basic biologic substrates. These isotopes mimic natural
molecules such as sugars, water, proteins, and oxygen.
 As a result, PET is often capable of revealing more about
the cellular level metabolic status of a disease compared
5
(Unit 12, Section 12.3)
10
10
SMU-DDE-Assignments-Scheme of Evaluation
with the capabilities of other imaging modalities.
Currently,
the
most
commonly
used
PET
radiopharmaceutical is F-FDG.
FDG imaging pitfalls
 Tumor cells, however, are not the only cells that exhibit an
increased uptake of FDG. Because FDG maps glucose
metabolism, its distribution can be altered by any physical
activity. Normal physiologic accumulation of FDG occurs
in the brain, muscles, salivary glands, myocardium,
gastrointestinal tract, urinary tract, brown adipose tissue,
thyroid gland, and gonadal tissues.
 It is important to recognize and understand normal
variants of FDG uptake and benign disease to avoid
mistaking them with pathologic processes. The timing of a
patient’s last meal before a PET study will have a
considerable effect on the quantities of glucose and insulin
in the circulation, thereby affecting FDG uptake.
 Similarly, the patient’s state of hydration can alter the
distribution of FDG in the body by altering the patient’s
excretion of the tracer. To avoid confounding results that
may complicate image interpretations, patients are required
to fast from 4 to 6 hours before their PET examinations. If
the patient’s blood sugar level is more than 200 mg/dL
before the injection of FDG, this could limit the study’s
sensitivity.
 Although all diabetic patients should control their blood
sugar level with oral hypoglycemic medication or insulin,
the timing of an insulin injection may affect the PET scan.
An insulin injection close to the time of FDG
administration induces diffusely increased uptake of FDG
in the skeletal muscles. Therefore, insulin should be given
as far from the time of FDG injection as feasible.
*A-Answer
Note –Please provide keywords, short answer, specific terms, specific examples (wherever necessary)
***********