DOI:10.2214/AJR.06.5026
AJR 2006; 186:1200
© American Roentgen Ray Society
Helical CT in Acute Pulmonary Embolism
Kashif Ashraf and
Omer Ashraf
Department of Radiology Aga Khan University Hospital Karachi,
Pakistan
Medical College Aga Khan University Hospital Karachi,
Pakistan
We read with interest the article titled "Helical CT for the
Evaluation of Acute Pulmonary Embolism" by Patel and Kazerooni
[1]. While finding the
recommendation of the combined usage of CT pulmonary angiography (CTPA) and CT
venography as a "one-stop-shopping" test for ruling out pulmonary
embolism as most interesting and indeed justifiable, we believe there is room
for some comments.
Recent trials have indeed established the role of spiral CT as a rapid,
cost-effective, widely available, and noninvasive technique to safely rule out
acute pulmonary embolism. The advent of MDCT, with its ability to visualize
smaller subsegmental emboli that may be missed with single-slice technology,
and increasing familiarity with the technique may ascertain its place globally
as the primary screening tool for the detection of emboli to the central and
peripheral pulmonary vasculature.
In comparison with V/Q scintigraphy, the authors quote greater accuracy
rates of CTPA in detection of acute pulmonary embolism as a reasonable
justification for a substitution in the conventional diagnostic algorithm.
However, in most of the comparative studies to date, conventional perfusion
imaging has been evaluated versus modernday tomographic scanners, yielding
somewhat inconsistent and prejudiced results. An examination with V/Q lung
scans in SPECT technique using an ultrafine aerosol
[2] showed excellent results
with diagnostic accuracy comparable to MDCT, with SPECT showing a superior
sensitivity. Similarly, the implementation of digital subtraction technique in
catheter pulmonary angiography has led to increased diagnostic yield. Usage of
imaging advancements in these conventional screening techniques may tilt the
balance against CT, in terms of the scientific advance promised by the latter.
These concerns need to be addressed in order to prevent deterrence of the
universal acceptance of CTPA as the primary screening tool in acute pulmonary
embolism.
Helical CT, however, as the authors mention, holds several other advantages
over contemporary techniques, including identification of other pathologies of
the thorax and excluding differential diagnoses that may mimic pulmonary
embolism in clinical presentation. Right ventricular failure is known as the
most significant determinant of mortality in acute pulmonary embolism
patients. CT is useful for risk stratification via accurate identification of
right ventricular dysfunction
[3] and, uninfluenced by
increasing patient age [4] and
preexisting pulmonary pathology or pulmonary embolism (unlike V/Q scanning),
it therefore may be the most important predictor of patient outcome among
existing investigations.
When patient safety is argued in diagnostic radiology, debate often centers
on adequate radiation exposure. Even though the advent of MDCT may result in
incurring of a higher effective dose, as the authors mention, it is pertinent
to observe that this is compensated by the noteworthy reduction in the number
of nondiagnostic and total number of investigations found to be required per
patient [5].
While PIOPED II [6] may
indeed establish helical CT and venous-phase CT as first-line studies in
patient evaluation, the need is for global availability and familiarity with
the above-mentioned techniques in order to counter the fatality rate of one of
the most common causes of cardiovascular death, acute pulmonary embolism.
References
- Patel S, Kazerooni EA. Helical CT for the evaluation of acute
pulmonary embolism. AJR 2005;185
: 135-149[Abstract/Free Full Text]
- Reinartz P, Wildberger JE, Schaefer W, Nowak B, Mahnken AH, Buell
U. Tomographic imaging in the diagnosis of pulmonary embolism: a comparison
between V/Q lung scintigraphy in SPECT technique and multislice spiral CT.
J Nucl Med 2004;45
: 1501-1508[Abstract/Free Full Text]
- Lim KE, Chan CY, Chu PH, Hsu YY, Hsu WC. Right ventricular
dysfunction secondary to acute massive pulmonary embolism detected by helical
computed tomography pulmonary angiography. Clin
Imaging 2005; 29:16
-21[CrossRef][Medline]
- Righini M, Bounameaux H, Perrier A. Effect of age on the
performance of single detector helical computed tomography in suspected
pulmonary embolism. Thromb Haemost 2004;91
: 296-299[Medline]
- O'Neill J, Murchison JT, Wright L, Williams J. Effect of the
introduction of helical CT on radiation dose in the investigation of pulmonary
embolism. Br J Radiol 2005;78
: 46-50[Abstract/Free Full Text]
- Srivastava SD, Eagleton MJ, Greenfield LJ. Diagnosis of pulmonary
embolism with various imaging modalities. Semin Vasc
Surg 2004; 17:173
-180[Medline]
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