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.
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.
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
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 and
subsegmental pulmonary arteries using thinner collimation.
Remy-Jardin et al
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).
Patel et al
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 2.5-mm
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.
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.
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.
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
demonstrated that CT venography (CTV) is comparable with US in the
evaluation of DVT with a sensitivity and specificity of 100%. Garg
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
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
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
breath-hold, 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
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 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
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
<1% incidence of fatal PE in the event of a negative CTPA.
Currently, a multicenter trial, the Prospective Evaluation of
Pulmonary Embolism Diagnosis II (PIOPED II) is underway to evaluate
the accuracy of multislice CT in the diagnosis of PE and DVT.
1. Remy-Jardin M, Remy J, Artuad D, et al. Peripheral pulmonary
arteries: Optimization of the spiral CT acquisition protocol.
2. Patel S, Kazerooni EA, Gross BH. Optimization of small
pulmonary artery visualization for pulmonary embolism detection
with multidetector CT [abstract].
3. Qanadli SD, Hajjam ME, Mesurolle B, et al. Pulmonary embolism
detection: Prospective evaluation of dual-section helical CT versus
selective pulmonary angiography in 157 patients.
4. Loud PA, Katz DS, Klippenstein DL, et al. Combined CT
venography and pulmonary angiography in suspected thromboembolic
disease: Diagnostic accuracy for deep venous evaluation.
AJR Am J Roentgenol.
5. Garg K, Kemp JL, Wojcik D, et al. Thromboembolic disease:
Comparison of combined CT pulmonary angiography and venography with
bilateral leg sonography in 70 patients.
AJR Am J Roentgenol.
6. Duwe KM, Shiau M, Budorick NE, et al. Evaluation of the lower
extremity veins in patients with suspected pulmonary embolism:
Retrospective comparison of helical CT venography and sonography.
AJR Am J Roentgenol.
7. Svenson SJ, Sheedy PF, Ryu JH, et al. Clinical outcomes of
patients with suspected acute pulmonary embolism after a negative
CT scan. Presented at the 23rd Annual Scientific Session of the
SCBT/MR, March 2000.
Abdominal CT Angiography in the Era of Multidetector
Marc J. Fenstermacher, MD; Silvana Faria, MD; Paul M.
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. 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.
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 <20 seconds with 1.25-mm
collimation. This is repeated during multiple phases of contrast
enhancement when indicated, so that arterial, portal venous, and
delayed venous phases may be acquired. When reconstructed with an
interval of 0.63 mm, and transferred to a workstation for
angiographic image creation, the result is very high-quality curved
and multiple oblique reformations depicting the anatomy and
pathology of interest optimally (Figure 1). Pertinent vessels are
demonstrated, the adjacent soft tissues are well-depicted and their
relationship to vessels visualized. In the oncologic setting,
tailoring the examination to each clinical situation allows the
radiologist to provide the angiographic images needed by the
clinician as well as the appropriate phase(s) of contrast-enhanced
axial images for evaluating other organs, such as the liver. Our
current technique on a GE LightSpeed QX/I unit (GE Medical Systems,
Milwaukee, WI) includes the following parameters: 1.25 mm thick,
slice pitch 6 (beam pitch 1.5), 0.8 second rotation speed, interval
0.63 mm, kV 120, mAs 340. The slice collimation can be increased to
2.5 mm, if necessary, for coverage. SmartPrep (GE Medical Systems)
is utilized, with a region of interest over the upper abdominal
aorta, to time the arterial phase as close as possible to the
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
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
time-consuming 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 reconstructions personally. The choice of optimum
angiographic display (shaded surface display, MIP reconstruction,
curved reformation and/or multiple oblique reformation) should be
individualized for each case.
Recently published studies have begun to document the utility
and accuracy of MDCT angiography.
Although the techniques are still under development and systematic
evaluation, this method of noninvasive angiographic imaging
promises to supplant MRA for many applications.
1. Kaatee R, Beek FJA, de Lange EE, et al. Renal artery
stenosis: Detection and quantification with spiral CT angiography
versus optimized digital subtraction angiography.
2. Rubin GD, Shiau MC, Leung AN, et al. Aorta and iliac
arteries: Single versus multiple detector-row helical CT
3. Matsumoto A, Kitamoto M, Imamura M, et al. Three-dimensional
portography using multislice helical CT is clinically useful for
management of gastric fundic varices.
AJR Am J Roentgenol.
Imaging Considerations in Pediatric Multislice CT: A
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.
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
Shortly after their release, several reports indicated that GE
LightSpeed multislice systems (GE Medical Systems, Milwaukee, WI]
delivered more radiation to patients when properly compared
(apples-to-apples) with single-slice CT scanners.
With subsequent deployment of multislice scanners, a sense of
unease has arisen in utilizing these scanners for pediatric
imaging. This presents a significant quandary since their increased
speed makes them highly desirable for pediatric imaging, while any
increased radiation dose prompts concerns regarding the long-term
effects of radiation in young patients.
In August 2000, we began routine imaging of pediatric patients with
our multislice units (GE LightSpeed). We initially decreased the mA
and increased the table speed (relative to the CT/i platform [GE
Medical Systems]) to minimize overall radiation dose and improve
image quality by reducing motion artifacts. In February 2001,
anthropomorphic pediatric phantoms were acquired and will be used
to refine pediatric CT protocols with respect to radiation
Our current technique is shown in Table 1, and we hope for
further decrease in radiation dose in the future.
Our initial calculations for multislice scanners (Table 2)
indicated a two- to four-fold increase in the dose compared with
conventional helical scanners when tested at identical kV and
mA-seconds per scan. Note that dose increased as collimation was
reduced. In the first two lines of Table 2, the 5-mm single-slice
conventional result was 0.8R; and 3.1R for the multislice unit
prior to an early upgrade, then fell to 1.9R after the focal spot
tracking upgrade was installed. The LightSpeed multislice scanner
upgrade installed in the summer of 2000 allowed compensation for
focal spot motion to be better controlled. This approach better
limits the radiation that is not effectively used by the
multidetector system. For 10-mm collimation, the single-slice
result was also 0.8R; and 2.1R for the multislice unit prior to the
upgrade. This dose then dropped to 1.3R after the upgrade. This
relatively increased dose on the LightSpeed 5-mm compared with the
10-mm slice thickness was because the collimator must be set to
produce a uniform fan beam of radiation across all of the detectors
in the z-axis direction. This, in turn, requires some "spill-over"
of radiation beyond the active detector surface, which increases
the dose proportionally higher in thinner-slice acquisitions. This
is especially important to note in young patients, who often have
thinner slices used to better define pathological 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 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
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
The authors would like to thank Dianna D. Cody, PhD, and Donna
M. Moxley, MS, from Diagnostic Physics for their valuable
1. Pappas JN, Donnelly LF, Frush DP. Reduced frequency of
sedation of young children with multisection helical CT.
2. McCollough CH, Zink FE. Performance evaluation of a
multislice CT system.
3. Cody DD, Moxley DM, Eftekhari F, Silverman PM. Pediatric dose
considerations in multislice helical CT.
Helical CT Today.
4. Motley DM, Hazle JD, Shepard JS, Zhou XJ. Dosimetry of a new
multislice helical CT scanner: Calculated and measured patient
5. Donnelly LF, Frush DP, Nelson RC. Multislice helical CT to
facilitate combined CT of the neck, chest, abdomen, and pelvis in
AJR Am J Roentgenol.
6. Brenner DJ, Elliston CD, Hall EJ, Berdon WE. Estimated risks
of radiation-induced fatal cancer from pediatric CT.
AJR Am J Roentgenol.
7. Paterson A, Frush DP, Donnelly LF. Helical CT of the body:
Are settings adjusted for pediatric patients?
AJR Am J Roentgenol.
Application of Six Sigma to Healthcare: Improving CT
Steve Venable, MBA and Paul M. Silverman, MD
Six Sigma is a performance improvement methodology used to
achieve significant change and improvement. The term
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,
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
found that <3% of patients needing IV contrast arrived in CT
without labs available (Figure 1). Today, the staff address issues
by collecting data first before stating the reasons for
Training is a key component in Six Sigma. All levels in the
organization must undergo training in the methodology and tools
used. At MDACC, the executive staff underwent 3 days of training at
a high level, the division leadership had 5 days, and the team
participants had 10 days. The commitment in resources and time is
substantial, but the payoff is extraordinary. Teaming with an
outside consulting group versed in Six Sigma methodology is
critical. After several projects are completed, the reliance on
outside services can be reduced.
The heart of the Six Sigma Methodology is the DMAIC process.
There are several acronyms but this reflects the gist of most:
the key objectives;
the baseline, benchmark the overall process;
the various processes performance;
the process, measure for desired affect;
the improved process.
The first task is to define or characterize the process and
problems. This provides the benchmark against which the
improvements can be measured. We discovered that many long-held
perceptions were inaccurate.
: "Many" patients reported without the requisite labs;
: <3% were missing laboratory tests.
: CT scanners were a bottleneck to efficient patient scanning;
: CT scan time averaged 3 minutes per patient, the shortest cycle
Why in CT?
At MDACC we suffered from limited CT capacity (with patients
going elsewhere for CT studies), high CT technologist turnover,
long patient wait times, and a stressful work environment. Several
performance initiatives had been completed through Diagnostic
Radiology prior to Six Sigma, but none had addressed the
fundamental problems. The challenge was to address these issues
The patient process was analyzed and broken into several
subprocesses to understand the cause of patient delays. The result
was a 75% reduction of the average patient wait for a CT exam, from
1 hour to 15 minutes. It was realized that two distinct processes
were taking place, one relating to the patient and one of
interpreting the studies. Subprocesses such as scheduling, patient
prep, and the CT exam were driven by the patient, not by the exam
or its type. The subprocesses of interpretation and report
generation were driven by the number of individual procedures
performed, not by the patient.
CT scan time did not limit capacity, the processes leading to
and following the CT scan were the bottlenecks. The CT scanners
were idle for many minutes per hour. The key to improving CT
capacity was to identify and remove the bottlenecks. This reduced
patient wait times and improved patient satisfaction, reducing
staff stress by reducing patient complaints. MDACC moved from
performing 207 procedures per day on 6 CT scanners to 272
procedures per day, a 31% increase on the same installed scanner
base. Today, we average 320 procedures per day on 6.5 scanners.
The actual time the CT scanner is dedicated to a patient was 23
minutes, regardless of the type or number of CT exams performed on
a patient. This was due to use of high-speed helical scanners, with
scan time never >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