Two basic questions usually neglected: the definition of the technical parameters and contrast injection

Tain Lee

Department of Radiology
Taichung Veterans General Hospital
No. 160, Section 3, Taichung Harbor Road
Taichung 407
Taiwan, ROC
Faculty of Medicine
Medical College of Chung Shang
Medical University
Taiwan
ROC

I-Chen Tsai

Department of Radiology
Taichung Veterans General Hospital
No. 160, Section 3, Taichung Harbor Road
Taichung 407
Taiwan
ROC
Tel: +886 4 2359 2525 3700
Fax: +886 4 2359 2639
E-mail address: sillyduck{at}vghtc.gov.tw

Wei-Lin Tsai

Department of Radiology
Taichung Veterans General Hospital
No. 160, Section 3, Taichung Harbor Road
Taichung 407
Taiwan
ROC

Min-Chi Chen

Department of Radiology
Taichung Veterans General Hospital
No. 160, Section 3, Taichung Harbor Road
Taichung 407
Taiwan
ROC

Ming-Yi Hsue

Department of Radiology
Taichung Veterans General Hospital
No. 160, Section 3, Taichung Harbor Road
Taichung 407
Taiwan
ROC

Wan-Chun Liao

Department of Radiological Technology
Chung Tai Institute of Health Sciences
and Technology
Taiwan
ROC

In their article published online on 19 April 2005, Leschka et al.1 shared the first experience of the new 64-slice MSCT. The adequate sample size and evaluation of performance without beta-blocker make the article of high reference value. However, we have several questions to the authors.

First, the authors mentioned that the scanner was a 64-MSCT with only 32-detector rows. About the collimation, though the z-sharp technology is used, the total collimation will not be doubled.2 The actual coverage of the collimation should be 32x0.6 mm, but the authors chose to represent it as 64x0.6 mm2, which is not a uniformly recognized way. To our knowledge, the z-sharp technology increases the sampling rate and decreases the aliasing along the z-axis, which contributes to good z-axis quality but not coverage.

Secondly, the definition of the pitch is also confusing. The generally used definition of spiral pitch is the table feed divided by the total coverage.3 The pitch of the authors' scanner should be 0.48 by our calculation, but the authors presented it as 0.24 without further explanation. Using a pitch of 0.48 to do CT coronary angiography is considered to be the major reason for the reduced scan time in this novel scanner.

Then, regarding the detector rows, were all the detector rows used while examining? If not, the collimation would be <32x0.6 mm. Because of the need for high quality, some machines use only the inner detectors for reducing cone beam artefact.4 Was that the condition in the study?

The final question is about the contrast injection technique. We have noticed that in the quality of vessel visualization of RPDA and PLA, the portions of ‘excellent’ were less when compared with other segments. Besides calcification, poor opacification also contributes much. Will the authors provide particular explanation for this? We have noticed that the contrast injection time (16 s) is almost equal to the post-threshold delay (5 s) plus scan time (median 11.2 s) in the study. In our personal experience with 40-MDCT, this setting can yield good result in slow heart rate patients. However, in patients with high heart rate (i.e. >80 b.p.m.), owing to the dilution effect of high cardiac output, the end of the scan (which is in PDA, PLA, and LV apex) is usually compromised by decreased contrast enhancement. We suggest that the authors increase the contrast injection time, either by decreasing the flow rate or by increasing the total contrast amount. We prefer the previous approach because the flow rate of 5 mL/s actually exceeds the right heart pump-in capacity in some patients.5

With the advance of CT technology, it is very helpful and meaningful to publish articles about clinical application and performance. The analysis and methodology are good in this article; in the near future, the article is likely to be cited frequently. However, as the technology itself is one of the main points in the study, a more precise description of the technical parameters will make this article even better.

References

  1. Leschka S, Alkadhi H, Plass A, Desbiolles L, Grunenfelder J, Marincek B, Wildermuth S. Accuracy of MSCT coronary angiography with 64-slice technology: first experience. Eur Heart J. http://eurheartj.oupjournals.org/cgi/rapidpdf/ehi261v1 (19 April 2005)
  2. Flohr T, Stierstorfer K, Raupach R, Ulzheimer S, Bruder H. Performance evaluation of a 64-slice CT system with z-flying focal spot. Rofo 2004;176:1803–1810.[ISI][Medline]
  3. International Electrotechnical Commission 60601-2-44. Amendment 1: medical electrical equipment, part 2–44: particular requirements for the safety of x-ray equipment for computed tomography. Geneva, Switzerland: International Electrotechnical Commission, 2002.
  4. Nieman K, Cademartiri F, Lemos PA, Raaijmakers R, Pattynama PMT, de Feyter PJ. Reliable noninvasive coronary angiography with fast submillimeter multislice spiral computed tomography. Circulation 2002;106:2051–2054.[Abstract/Free Full Text]
  5. Blomley MJK, Dawson P. Bolus dynamics: theoretical and experimental aspects. Br J Radiol 1997;70:351–359.[Abstract/Free Full Text]




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