**9. References**

198 Pulmonary Embolism

severe cases both ventilation and perfusion are reduced or abolished and matched defects are then frequently found (Li et al., 1994). Another sign of pneumonia that often has been described is the "stripe sign" (Sostman & Gottschalk, 1982, 1992). The "stripe sign" refers to the observation of a stripe of a relatively well preserved perfusion adjacent to the pleural surface, by contrast with the more pronounced perfusion defects within the pneumonic lesion. This distinguishes pneumonia from the segmental perfusion defects found in PE. The enhanced performance of V/P SPECT compared to planar imaging has facilitated the

Hampson as well as the ICOPER study illustrated that the risk of PE is increased in patients with pneumonia or other coexisting diseases (Elliott et al., 2000; Hampson, 1995). In the ICOPER study, 17% of 2000 patients with confirmed PE had infiltrates on chest X-ray. Pneumonia has also been shown to be a common finding in patients with autopsy proven

The doses of 30 MBq and 120 MBq for ventilation and perfusion, respectively, allows excellent V/P SPECT quality at an effective radiation dose of 1.8 mSv (ICRP, 1998). The absorbed dose to the breasts with V/P SPECT is 0.8 mGy (ICRP, 1998). Estimation of exposure is relatively easy when short-lived radio-isotopes are used in nuclear medicine. In contrast, for X-ray technologies this is much more difficult because of a number of factors, such as differences in equipment and the size of the exposed fields. According to ICRP, the average effective dose for 4–16-detector MDCT is 5.4 mSv (Valentin, 2007). Notably, this information was based on computed rather than measured dose data. Hurwitz et al. reported for a current adult PE protocol with 64-detector MDCT a measured effective dose of 19.9±1.38 mSv (Hurwitz et al., 2007). These authors point out that the actual measured dose is about 50% higher than the computed dose. The absorbed dose to the breasts was 35–42 mGy. Absorbed radiation dose to the breast for a single-slice CT study was 20–50 mGy and 30– 50% greater with a four-slice CT. In a very recent study, Hurwitz et al. (Hurwitz et al., 2009) studied radiation dose-saving protocols. Phantoms of women were exposed to MDCT protocols with automatic current modulation, lower tube voltage and bismuth shields over the chest. In the case of a medium sized female patient when automatic current modulation was applied at 140 kVp, breast doses were estimated at 62 mGy and this reduced to 33 mGy when bismuth shields were added. At 120 kVp the doses were 44 mGy without shields and 20 mGy with shields. Some limitations of the study were discussed. No phantom with significant subcutaneous fat was studied. The authors were not able to directly assess the effect of

increased noise for the diagnosis of PE. Dose-saving protocols are promising.

V/P SPECT, it is also possible to diagnose other cardiopulmonary conditions.

reproductive period and during pregnancy.

The superiority of V/P SPECT over other imaging techniques in the diagnosis of PE has been well demonstrated. The examination is without contraindication and can be performed in 99% of patients with suspected PE. V/P SPECT makes it possible to quantify the extent of perfusion loss, so that PE treatment can be better adapted to the needs of individual patients. By using

Because of the very low radiation exposure, it is an ideal method for evaluating treatment and follow up. Low radiation doses are particularly important for women in the

detection of the stripe sign (Pace & Goris, 1998).

PE (Mandelli et al., 1997).

**7. Radiation exposure** 

**8. Conclusions** 


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**10** 

*1China 2USA* 

**Dual Source, Dual Energy Computed** 

**Tomography in Pulmonary Embolism** 

*1Department of Medical Imaging, Jinling Hospital, Clinical School of Medical College,* 

More than 650,000 cases of pulmonary embolism (PE) are reported each year, resulting in an estimated 300,000 annual fatalities. This level of occurrence ranks PE as the third leading cause of death in the USA [ Laack TA, 2004; Tapson VF, 2008]. Multidetector CT (MDCT) pulmonary angiography has now largely replaced ventilation/perfusion scintigraphy and conventional pulmonary angiography for the evaluation of possible PE [Patel S,2003]. In 2007, MDCT pulmonary angiography was accepted as the reference standard for diagnosis of acute PE **[**Remy-Jardin M,2007**]**. However, conventional MDCT pulmonary angiography only provides morphological information and its ability to assess subsegmental pulmonary arteries is variable: sensitivities range from 37%–96%. The ability to assess subsegmental

In the past, various CT techniques have been developed to evaluate the assessment of lung perfusion in patients with suspected PE. (1) Dynamic multi-section electron beam CT **[**Schoepf UJ,2000**].** This perfusion-based CT technique had a scanning volume of 7.6 cm, required a long patient breathhold, and delivered a high additional radiation dose to the patient. (2) Color-coding the density of lung parenchyma in contrast-enhanced CTA **[**Wildberger JE,2001**]**. This technique is of limited use when lung diseases, such as groundglass opacities (e.g., in pulmonary edema or pneumonia) were present.(3)A subtraction CTA technique of whole-thorax multi-detector CT scans acquired before and after intravenous contrast within a single breathhold. This technique was limited by a longer breathhold time, misregistration artifacts because of the mismatched unenhanced and contrast-enhanced scans, and additional radiation dose caused by the fact that an additional unenhanced scan had to be performed to assess the iodine distribution in the lung

Recently, DECT with different dual energy CT hardware (dual source CT and rapid kV switching technique) became available to simultaneously provide the functional and morphological information, overcoming the limitations of the above-mentioned CT

pulmonary arteries has increased with advances in MDCT technology.

**1. Introduction** 

[Wildberger JE,2005].

Yan'E Zhao1, Long Jiang Zhang1, Guang Ming Lu1,

*Medical University of South Carolina, Ashley River Tower* 

Kevin P. Gibbs2 and U. Joseph Schoepf2

*Nanjing University, Nanjing, Jiangsu Province 2Department of Radiology and Radiological Science* 

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