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Pulmonary embolism (PE) and deep venous thrombosis (DVT)
are components of the same disease entity, accounting for
300,000 to 600,000 hospitalizations and 50,000 to 100,000
deaths a year in the United States. Since appropriate treatment is estimated
to decrease the mortality by 30%, early and accurate diagnosis
is essential. Until recently, many different imaging tests were used to
evaluate pulmonary thromboembolic disease and thrombosis of the
deep veins of the lower extremity. Ventilation perfusion scintigraphy
(V/Q) has been the mainstay in the diagnosis of PE, with pulmonary
angiography being the gold standard. However 40% to 70% of V/Q
scans are nondiagnostic, thereby requiring additional testing for the
diagnosis or exclusion of PE. Pulmonary angiography is an invasive
test with a major complication rate of 1.3%. For the last 5 years, helical
(spiral) CT has been used in the diagnostic evaluation of thromboembolic
disease.
The advent of faster helical scanners, particularly multislice scanners,
has revolutionized the diagnosis of not only clinically significant
central pulmonary emboli, but has also greatly improved the detection
of subsegmental pulmonary emboli. 1-3 Faster scanning times, single
breath-hold acquisitions, and thinner collimation has led to improved
detection of both segmental and subsegmental pulmonary emboli with
the diagnostic accuracy of CT pulmonary angiography (CTPA)
approaching that of catheter angiography. 3 Therefore, CTPA is commonly
used as a diagnostic modality of choice, especially in patients
with an abnormal chest radiograph or underlying pulmonary disease,
as both increase the frequency of a nondiagnostic V/Q scan. CTPA is
also valuable as it yields an alternative diagnosis in 40% to 70% of
patients with a negative PE scan, including bronchogenic carcinoma,
metastatic disease, pericardial effusion, and aortic dissection. Recent
studies demonstrate significantly improved visualization of segmental
Paul M. Silverman, MD
Editor-in-Chief
Professor of Radiology
Gerald D. Dodd, Jr. Distinguished Chair Diagnostic Imaging
Section of Body Imaging
University of Texas M.D. Anderson Cancer Center
Houston, TX
Contributing Editors
Smita Patel, MRCP, FRCR, Lecturer II
University of Michigan Health System, Ann Arbor, MI
Marc J. Fenstermacher, MD, Assistant Professor
University of Texas M.D. Anderson Cancer Center, Houston, TX
Farzin Eftekhari, MD, Professor
University of Texas M.D. Anderson Cancer Center, Houston, TX
Steve Venable, MBA, Senior Management Analyst
University of Texas M.D. Anderson Cancer Center, Houston, TX
V O L U M E 1 • I S S U E 1 • 2 0 0 1
CT UPDATE
Multislice CT: A New Comprehensive Tool for Evaluation
of Pulmonary Embolism and Deep Venous Thrombosis
Smita Patel, MD, MRCP, FRCR; Ella A. Kazerooni, MD; Paul M. Silverman, MD
and subsegmental pulmonary arteries using thinner collimation.
Remy-Jardin et al 1 reported improved visualization of the segmental
pulmonary arteries from 85% to 93% and that of the subsegmental
vessels from 37% to 61% using the 2-mm technique compared with
the 3-mm technique with single-detector CT scanner (SDCT). 1 Patel
et al 2 recently reported an incremental improvement in visualization of
the segmental arteries from 74% to 79% to 89%, respectively, when
comparing the 3-mm collimation technique using SDCT with the 2.5mm
and 1.25-mm techniques using multidetector CT (MDCT). The
incremental improvement was even better at the subsegmental levels,
35% with the 3-mm technique and 44% and 68% with the 2.5-mm and
1.25-mm techniques, respectively. 2 Not only were arteries seen more
clearly, but reader agreement as to presence or absence of thrombus in
segmental and subsegmental vessels was more consistent with the
1.25-mm collimation technique. A recent large study compared the
performance of dual-section helical CT with pulmonary angiography
and concluded that the sensitivity, specificity, and positive- and negative-predictive
values were 90%, 94%, 90%, and 94%, respectively. 3
They concluded that helical CT may replace pulmonary angiography
in the diagnosis of PE and that selective pulmonary angiography
should be reserved for patients with an unresolved diagnosis. 3
Ultrasonography (US), the most commonly used diagnostic tool for
the evaluation of DVT, has a sensitivity of 95% and a specificity of 98%
for the diagnosis of acute DVT. Currently, direct catheter venography,
plethysmography, and isotope scanning are not often used. Recently,
several investigators have compared US and helical CT in patients with
suspected PE. Some authors advocate US to exclude a DVT in the event
of a negative CTPA, thereby excluding clinically significant pulmonary
embolism and the need for unnecessary anticoagulation, which has its
own associated morbidity. However, this is at the expense of two different
tests that take longer to perform, not to mention the additional costs.
With the advent of newer and faster helical CT scanners, in particular
multislice scanners, a single comprehensive exam can be performed to
evaluate the pulmonary arterial bed and the deep veins of the pelvis and
thighs. In a study of 71 patients, Loud et al 4 demonstrated that CT
A B
FIGURE 1. (A and B) Axial contrast-enhanced MDCT in a patient with
metastatic breast cancer, demonstrating filling defects in the lobar (arrows),
segmental (curved arrows), and subsegmental (arrowheads) pulmonary
arteries, compatible with PE. Note the bilateral pleural effusions and a pericardial
effusion. Mild enlargement of the subcarinal nodes is also noted.

FIGURE 2. Axial contrast-enhanced
MDCT of the pelvis demonstrating
normal optimal enhancement of the
femoral veins (arrows).
venography (CTV) is comparable
with US in the evaluation of DVT
with a sensitivity and specificity of
100%. Garg et al 5 reported obtaining
a good quality CTV examination
in 97% of a total of 70
patients. They demonstrated that
CTV was more efficacious than
US in 36% of cases, equivalent to
US in 37%, and US was better
than CTV in 27%. Duwe et al 6
found an accuracy of 93% for
CTV using US as the reference
test in 74 patients, with a sensitivity of 89%, specificity of 94%, positive-predictive
value of 67%, and negative-predictive value of 98%.
The CTV techniques used by these authors differ, with the scan interval
varying from 5 mm to 20 mm, collimation 5 mm to 10 mm, and the
injection delay from 3 minutes to 3.5 minutes. All of these studies were
performed on a single-detector helical scanner. CTV is particularly useful
in postoperative patients or in obese and immobile patients in whom
sonography can be challenging to perform.
Multi-detector CT Scan Protocol: Part 1–Thorax
For the thorax protocol, 150 cc of iohexol 300 mg/mL
(Omnipaque ® [iohexol]; Amersham Health, Princeton, NJ) is injected
via a 20-gauge angiocatheter in an antecubital vein at a rate of 4
cc/sec. A scan delay of 25 seconds is used. Imaging is performed from
the dome of the diaphragm to the aortic arch during a single breathhold,
with the acquisition time varying between 15 to 19 seconds,
depending on the size of the patient. Images are obtained at 1.25-mm
collimation and reconstructed at 50% of the scan collimation (HS
mode, pitch 6).
Part 2–Leg/pelvic veins
Three minutes following start of the contrast injection, acquisition
of the pelvis and lower extremity veins is obtained from a caudad to
cephalad direction from the level of the tibial plateaus to the iliac
crests. Images are obtained at 7.5-mm collimation and reconstructed at
50% of the scan collimation (HS mode, pitch 6). The entire study is
then evaluated on a GE Advantage Windows Workstation (GE
Medical Systems, Milwaukee, WI). Use of the HS mode in large
patients may account for very noisy images, limiting evaluation of the
pulmonary arteries. In these patients, the HQ mode can be used and
thicker slices obtained. Acquisition of the pulmonary arteries and the
deep veins of the pelvis and thighs is obtained with a single bolus of
intravenous contrast.
Study Interpretation
The window level and width is altered for optimum evaluation of the
pulmonary arteries. A wider window width and a higher level may be
needed to evaluate for subtle emboli. Depending on the concentration
of the contrast in the pulmonary arteries, this may need to be altered at
different levels. Then, the main, lobar, segmental, and subsegmental
arteries are examined systematically from their origins to the 5th or 6th
order branches, using the scrolling mode device. Pulmonary emboli are
diagnosed as partial or complete filling defects, enlargement of the
pulmonary artery with a large occlusive clot, peripheral filling defect,
or nonenhancement of a segment of the pulmonary artery (Figure 1).
Evaluation for chronic pulmonary emboli is also possible, with the
presence of webs or detection of small thick-walled pulmonary arteries
with enhancing walls and filling defects. Systematic review of the
entire pulmonary arterial circulation is performed bilaterally. Note is
also made of additional findings such as pleural or pericardial effusions,
nodules, tumors, nodal enlargement, consolidation, emphysema, and
2
aortic dissection or aneurysm. These aid clinicians in further management
as the clinical presentation of the above diagnoses can be similar.
Then, the veins of the pelvis and thighs are evaluated using the scroll
mode device, after narrowing the window width and level, for optimum
evaluation of the veins.
DVT is diagnosed when there is a central filling defect, enlargement
of the vein (pitfall, venous valves), segmental nonvisualization, wall
enhancement, or perivenous subcutaneous edema (Figures 2 and 3).
Prolonged arterial enhancement may represent extensive bilateral DVT.
However this can also be found when the CT is performed too soon in
the arterial phase or when there is severe bilateral arterial insufficiency.
Observation of other pathology is also possible, such as pelvic tumor
compressing the pelvic veins or a Baker’s cyst. Optimum venous
enhancement is not uniform in all patients with an injection-to-scan
delay of 3 minutes, as this varies according to the patient’s cardiac status
and the state of the pelvic and lower limb arteries. Patients with
altered inflow due to atherosclerotic disease may require a longer delay
time.
Multislice CT allows acquisition of 4 to 8 axial images with each
revolution of the helical scanner, hence accounting for the short scan
acquisition time, which is essential in sick, dyspneic intensive-care
patients who cannot hold their breath. Not only has multislice CT
improved evaluation of the segmental and subsegmental pulmonary
arteries, but it has also allowed evaluation of the lower extremity veins,
the source of PE, with a single injection of intravenous contrast. This
translates into a single imaging modality for a quick, accurate, and efficient
diagnosis of pulmonary thromboembolic disease. Recent studies
have demonstrated

TECHNICAL ISSUES
Abdominal CT Angiography
in the Era of Multidetector CT
Marc J. Fenstermacher, MD; Silvana Faria, MD;
Paul M. Silverman, MD
As new techniques have emerged over the last 15 years, the imaging
evaluation of the vessels of the abdomen has undergone considerable
evolution. Prior to the advent of multidetector CT (MDCT), much
of the advancement has been in magnetic resonance angiography
(MRA). A number of innovative MRA techniques have been utilized,
including 2-dimensional (2D) and 3-dimensional (3D) time-of-flight
(TOF), phase contrast, and, most recently, bolus contrast-enhanced 3D
fast gradient echo techniques, with or without step-wise incremental
couch movement. Currently, the latter approach is widely utilized in
most practices, especially for the evaluation of the arterial and portal
venous systems. The systemic venous system remains a challenge for
accurate, high-contrast MRA, primarily because of the relatively low
concentration of injected gadolinium once it reaches the iliac veins and
inferior vena cava. All of the MRA techniques in the abdomen share a
number of drawbacks, which have fueled the search for better noninvasive
angiographic techniques. With MRA, it is not possible to
demonstrate both the vasculature and the regional soft tissues in the
same imaging sequence; the highest quality arterial MRA will demonstrate
bright vessels and practically nothing else. This problem is particularly
limiting in the oncologic setting, where noninvasive angiography
is used primarily to stage tumors locally and in surgical planning.
Even high-quality abdominal MRA techniques still suffer relatively
low spatial resolution due to the requirement of imaging in the
coronal plane for adequate coverage, with a large field-of-view, yet
avoiding wrap-around aliasing artifacts. Tertiary or smaller branches
are not visualized due to limitations in resolution and slice thickness.
A B
C
D
FIGURE 1. Comparison of magnetic
resonance angiography (MRA) and
computed tomography angiography
(CTA) in a patient with testicular cancer
and a left para-aortic nodal
mass. This preoperative evaluation
was performed prior to retroperitoneal
lymph node dissection. (A)
Coronal MIP projection from 3D
bolus contrast-enhanced MRA in the
arterial phase. (B) Double oblique
coronal CTA reformation showing
two right renal arteries and single left
renal artery. (C and D) Two curved
CTA reformations showing the (C)
upper and (D) lower right renal arteries,
and the left para-aortic nodal
mass abutting the undersurface of
the left renal artery.
3
Any patient motion during the 20- to 30-second breath-hold acquisition
degrades the MRA images severely.
With single-detector helical CT (SDCT), it first became possible to
reconstruct the 3D helix retrospectively with the acquired slice thickness
but with much smaller intervals, such as 50% of the collimation.
This enabled the creation of high-quality multiplanar volume reformations
and other angiographic images using a workstation, and we began
using this technique in selected cases for visualizing the arterial and
venous vasculature adjacent to tumors in the abdomen and pelvis. The
limiting factors with SDCT have been the interrelated issues of slice
thickness and coverage. All bolus-contrast-enhanced angiographic
techniques depend on matching the timing of image acquisition to the
transit of contrast through the vessels of interest. Since all acquisitions
are in the axial plane, there is limited coverage with the 2- to 3-mm collimation
and pitch of 2 usually used with SDCT. 1
The advent of MDCT has allowed the acquisition of larger areas of
coverage with thinner slice collimation and much faster imaging
times per series. We routinely image the entire abdominal aorta and
proximal common iliac arteries in

transit of the bolus of contrast through the aorta. An alternative to
SmartPrep, which does incur a nominal though mandatory delay
between contrast arrival in the abdomen and the initiation of scanning,
is to perform a test injection in order to estimate the contrast travel
time to the abdominal aorta. This step is time consuming and not used
routinely in our department at this time.
Data is transferred to a workstation, currently a Vital Images
Vitrea2 (Vital Images, Inc., Minneapolis, MN) or an Advantage
Windows workstation (GE Medical Systems), for creating and filming
curved and multiple oblique reformations. Although this is a timeconsuming
step for the radiologist, it is rewarding for the clinician.
While a technologist with special interest and training in image processing
can perform this step in many cases, optimizing reformatted
imaging planes often requires a knowledge of anatomy and pathology
that may be beyond their reach (Figure 2). At the current stage of
development of these techniques, interested cross-sectional radiologists
should be encouraged to perform the reformations and recon-
PRACTICAL ISSUES
Imaging Considerations in Pediatric
Multislice CT: A Radiologist’s Perspective
Farzin Eftekhari, MD and Paul M. Silverman, MD
Multislice CT, occasionally referred to as multidetector or multidetector
row CT, has made a significant impact on the imaging of
pediatric patients by reducing the total study time in uncooperative or
very ill patients. In many instances, this has virtually eliminated
breathing or motion artifacts, and, even more importantly, the need for
conscious sedation or general anesthesia. 1
In those patients who require conscious sedation or general anesthesia,
shorter examination time has minimized the sedation period,
and, thus, the potential risks of sedation or anesthesia. This has
increased patient throughput and the efficiency of the sedation team,
enabling them to schedule additional pediatric CT, magnetic resonance
(MR), or interventional radiology procedures.
Table 1. Technical Considerations in Pediatric Multislice CT
Approximate Approximate
DFOV mA kV Age (y) Weight (kg)

processes and to cover the smaller anatomy.
It is also important to realize that the source-to-detector distance is
decreased in the LightSpeed multislice scanner (94.9 cm) relative to
the GE single-slice design (109.9 cm). This detector alone accounts for
a 34% increase in radiation dose for the multislice system compared
with the single-slice configuration using identical scan parameters.
For pediatric abdominal/pelvic CT scanning, we use a slice thickness
of 5 mm, high speed (HS), and a table speed of 22.5 mm/rotation.
For pediatric chest CT, we use a slice thickness of 5 mm, HS,
and 22.5 mm/rotation table speed.
Pediatric patients receive iodinated contrast material when it is
clinically indicated. To limit reactions or nausea and vomiting, we use
low-osmolality contrast material (LOCM) at a dose of 1.5mL/kg
body weight for the chest, and 2.0 mL/kg for abdominal and pelvic
CT. We prefer to deliver all of the contrast before scanning and allow
a 25-second delay for chest, and chest/abdomen/pelvis imaging
(allowing a 12-second pause between chest and abdomen), and 50
seconds for abdomen/pelvis imaging. Alternatively, when available,
we use a computer automated scanning technology, such as
SmartPrep, to ensure that scanning occurs during peak liver enhancement.
This allows for consistency and optimal imaging to detect focal
liver lesions.
Injection rates for contrast material range from 0.3 to 3.0mL/sec,
depending on the size of the IV access line (22- to 18-gauge angiocatheters,
depending on the age of the child).
Our pediatric technique (Table 1) is based on the child’s body size
(depth of field of view), age, and weight. For children older than 6
years of age, we use a slice thickness of 7.5 mm and 15 mm/rotation
table speed. We use this table to select the appropriate mA setting for
each case. The mA ranges from 140 to 230 with a kV of 120. This
MEDICAL ECONOMICS
Application of Six Sigma to Healthcare:
Improving CT Efficiency
Steve Venable, MBA and Paul M. Silverman, MD
Six Sigma is a performance improvement methodology used to
achieve significant change and improvement. The term Six Sigma
refers to six standard deviations from the mean on a normal distribution
model. This level of performance would seem impossible to attain at
first, but the methodology leads to extraordinary improvement on
processes and final results. Many large corporations, including Allied
Signal, Honda, and GE, 1 have adopted Six Sigma to improve their
financial performance and maintain a competitive advantage.
Six Sigma represents a cultural shift to continuous, data-driven
performance improvement. Though Six Sigma was originally used to
decrease defects in manufacturing industries, it has moved to service
industries, and is readily adapted to healthcare. The data-driven
aspect of Six Sigma meshes well in the current hospital setting where
dramatic efforts are being made to strive for marginal efficiency in a
competitive environment. Physicians require a business methodology
based on verifiable data and analysis. This focuses all groups on solutions
to problems and quantitative measures of success.
At the University of Texas M.D. Anderson Cancer Center
(MDACC), we have used Six Sigma to provide a dramatic improvement
in efficiency. In computed tomography (CT), a common reason
given for patient delays was a lack of laboratory tests prior to the CT
scan. More than 95% of our patients received IV contrast and labs
were required prior to administering contrast. However, data analysis
5
table is designed for current GE multislice scanners in which the scan
time is 0.8 seconds. However, since newer scanners offer shorter scan
times, such as 0.5 seconds, we intend to update this table to adjust for
mA values accordingly.
Conclusion
We feel that the use of multislice CT scanners has had a significant
impact on imaging in pediatric patient population in terms of need for
sedation and throughput, but we need to continue to look for ways to
decrease the radiation dose to even lower levels.
Acknowledgments
The authors would like to thank Dianna D. Cody, PhD, and Donna
M. Moxley, MS, from Diagnostic Physics for their valuable comments.
REFERENCES
1. Pappas JN, Donnelly LF, Frush DP. Reduced frequency of sedation of young children
with multisection helical CT. Radiology. 2000;215:897-899.
2. McCollough CH, Zink FE. Performance evaluation of a multislice CT system. Med
Phys. 1999;26:2223-2230.
3. Cody DD, Moxley DM, Eftekhari F, Silverman PM. Pediatric dose considerations
in multislice helical CT. Helical CT Today. 2001;6(3):3-4.
4. Motley DM, Hazle JD, Shepard JS, Zhou XJ. Dosimetry of a new multislice helical
CT scanner: Calculated and measured patient doses [abstract]. Radiology.
1999;213(P):284.
5. Donnelly LF, Frush DP, Nelson RC. Multislice helical CT to facilitate combined CT
of the neck, chest, abdomen, and pelvis in children. AJR Am J Roentgenol.
2000;174:1620-1622.
6. Brenner DJ, Elliston CD, Hall EJ, Berdon WE. Estimated risks of radiationinduced
fatal cancer from pediatric CT. AJR Am J Roentgenol. 2001;176:289-296.
7. Paterson A, Frush DP, Donnelly LF. Helical CT of the body: Are settings adjusted
for pediatric patients? AJR Am J Roentgenol. 2001;176:297-301.
found that

measured. We discovered that many long-held perceptions were inaccurate.
Perception: “Many” patients reported without the requisite
labs; Reality: 3 minutes, even for a combined chest, abdomen,
and pelvis exam. We spent more time getting the patient onto and off
the table, and the setup and cleaning of the room, 20 minutes total.
The team concentrated on optimizing the patient-related activities and
removed the excess idle time of the CT scanners.
The Interpretive Process
The teams also analyzed the activities in the reading rooms. The
goal was to eliminate all nonvalue activities performed by the radiologists
and shift those activities to others, allowing the radiologists to
concentrate on film interpretation and reports. We began to print out
the information needed by the radiologists for protocoling the patients
putting pertinent information at their fingertips. We also began to hang
the motorized viewers continuously throughout the day, relieving the
radiologist of this tedious task. The results were a dramatic increase in
throughput in the reading rooms and the radiologists were able to stay
current with the growing patient activity.
During the characterization process, several processes were determined
not to need the full Six Sigma treatment, instead, a small group
could work out a solution. An example was the 50% turnover in CT
technologists. A working group interviewed the technologists and
analyzed external market issues. It was determined that the techs were
undercompensated compared with the local market and there were
inconsistencies in the work environment. Work volumes between
shifts and lack of communication between technologists on each shift
were problematic. As soon as changes were implemented to correct
these issues, turnover was reduced to 0% the following year.
Conclusion
When this Six Sigma project was initiated, we failed to realize its
size and scope. We also underestimated the manpower resources
required. Six Sigma touches the entire operation and the necessary
resources must be dedicated to the project. Cultural changes and the
fear of change must be overcome. Six Sigma is data rigorous and provides
a framework for disciplined analysis and correction of processes
not meeting the specification. The payoffs are tremendous for the
corporate culture, for patient satisfaction, and in increased throughput
(shortened patient wait times, faster exam times, decreased interpretation
time resulting), with financial benefits in the increased capacity
on the same resources. For the radiologist, we removed the nonvalue-added
activities in the reading rooms and developed closer working
relationships between the physician staff and technical and nursing
staff. Weaknesses in our information systems were identified and
detailed changes to the software were initiated. Our film printing system
was woefully inadequate and a new system was designed, purchased,
and installed to improve the film quality control function, add
more capacity, and remove the film printing bottleneck. The financial
returns for this project are projected at $15.8 million over 5 years. For
every dollar invested in this project, MDACC expects $16 in return.
The final lesson is that Six Sigma is never-ending; we monitor and
improve our processes continuously. As new areas come into focus, we
apply the tools and continue to reap the benefits of the program.
REFERENCES
1. Harry MJ, Schroeder R. Six Sigma: The Breakthrough Management Strategy Revolutionizing
the World’s Top Corporations. pp. vii-viii: 112. New York: Random House,
2000.
2. Harry MJ, Lawson JR. Six Sigma Producibility Analysis and Process
Characterization. pp. 4.2-4.4. Boston: Addison-Wesley Publishing Co., 1992.
FUTURE MEETINGS AND CONVENTIONS
Meeting date Meeting name Location Contact
November 1-8, 2001 American Society for Therapeutic Radiology and Oncology San Francisco, CA 703-502-1550
November 25-29, 2001 Radiological Society of North America Chicago, IL 630-571-2670
CT Update is published by Anderson Publishing, Ltd., 1301 West Park Ave., Ocean, NJ 07712 • (732) 695-0600.
O. Oliver Anderson, Publisher; Elizabeth A. McDonald, Managing Editor; Felice Ponger, Art Director.
Sponsored by an educational grant from Amersham Health. The views and opinions expressed in this publication are those of the authors and do not necessarily
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