J.Calatayud Moscoso del Prado, D. Castellón Plaza, C. Trinidad López, R. Prada González. POVISA, Vigo (SPAIN)

INTRODUCTION  Pulmonary embolism (PE) is a common chest disorder that annually affects 1.5 million people in Europe. 1-2% of hospital admissions resulting as many as fatalities per year and ranking PE as the third leading cause of death.  In recent years, Pulmonary MDCT-Angiography has been established as the method of choice for diagnosing acute pulmonary embolism (PE) replacing ventilation-perfusion lung scintigraphy and pulmonary angiography.

Advanced in multidetector CT have lead to improved spatial resolution, delineation of the peripheral pulmonary arteries, and detection of small emboli thereby increasing sensitivity and specificity in the diagnosis of pulmonary embolism. INTRODUCTION

 The conspicuity of the thrombus depends on the density difference between the trombus and the contrast enhanced artery. ?

INTRODUCTION  The degree of vessel enhancement depends on injection related-factors and on patient-related factors.

INTRODUCTION  Several studies consider diagnostically adequate for MDCT-PA attenuations of more than 200 HU.

INTRODUCTION Variability on vessel enhancement (HU)

INTRODUCTION Example: A 23 years old woman with suspected PE. Technically limited study HU < 200 CT-PA was repeated the day after using 120 ml of medium and decreasing the trheshold A thrombus in the right lower lobe segmentary artery was confirmed Pulmonary infarction it was seen. However it was difficult to detect PE

PURPOSE  To compare the degree of vessels enhancement in Pulmonary MDCT Angiography in two groups (A: 60 years old).  To evaluate the differences between image quality and patient characteristics in Pulmonary CT- Angiography.

MATERIALS AND METHODS  From June 2008 to March 2009  Patients referred for CT-PA to rule out PE were prospectively evaluated to assess the contrast enhancement in the main pulmonary artery.  The exclussion criteria were renal insuffiency, allergy to contrast material, hypertiroidism, pregnancy and age less than 18 years old.

 In total, 100 patients were reviewed.  Two groups were created depending on the age in: Group A Group A : <60 years old (n=40) Group B Group B : >60 years old (n=60) MATERIALS AND METHODS

 All scans were obtained using a 64 section Multidetector- CT (Somaton Sensation 64, Siemens). A standard collimation of 0.6mm was used with a gantry rotation speed of 0.5 second and a pitch factor of 1.1  Patient were scanned with a kilovoltage of 100Kv and a tube current level of 90mAs  MDCT-PA was obtained in a caudo-craneal direction during a single inspiratory breath-hold

MATERIALS AND METHODS Vessels opacification was provied by IV injection of 90ml of iopromide 300mg I/mL via a peripheral vein followed by a saline flush of 20 ml. Flow rate was kept constant at 4ml/sg.

MATERIALS AND METHODS  Scanning delay was determined by using a bolus tracking technique.  Contrast enhancement was measured placing a circular ROI of 10mm in diameter over the main pulmonary artery after the reference CT image was obtained. 10 mm

MATERIALS AND METHODS  Diagnostic CT was triggered automatically 5 seconds after contrast enhancement exceeds a predefined threshold of 132 HU. 132HU

 Age, Sex and the existence or absence of PE were documented.  Furthermore, weigh and height was measured in all patients in the scan room before the MDCT-PA and body mass index (BMI) was calculated from these data.  Pulmonary vessel enhancement and image noise were quantified.  Subjetive vessel contrast was assessed by two radiologist in consensus. MATERIAL AND METHODS

 For further post processing, thin-slice reconstruction was performed with slice thickness of 1 mm, an increment of 0.7 and a smooth reconstruction kernel (B20).  Final image analysis was performed on axial images and on coronary maximum intensity projections (MIP) with slice thicknesses of 3 and 6mm, respectively. MATERIAL AND METHODS

 The measurement of background noise was based on assessment of Hounsfield units within surrounding air at three different regions of interest in front of the patient using a ROI of 1 cm 2.  Averaged values were used for final calculation of background noise. MATERIAL AND METHODS mean pulmonary vessel SI SNR = background noise mean pulmonary vessel SI SNR = background noise

MATERIAL AND METHODS  Statistical results were calculated using SPSS software(v for Windows)

MATERIAL AND METHODS Statistical Analysis  Pearson Correlation Coeficient Relationship between quantitative patient charactersitics and quantitative variables of image quality. Display of calculated data was performed with regression lines based on univariate linear regression.  t - Student To compare imaging parameters between categorical variables for unpaired variables  Chi- Square ( Χ i 2 ) To compare proportions in both groups.  Kruskal-Wallis To compare ordinal varibles between two groups

 A total of 100 patients were included in the study (mean age 60,87± 20,28 years (range: 21 to 102 years)  Mean pulmonary arterial attenuation was 340,1 ± 118,9 HU (Range HU).  Mean body weight: 75,75 ± 16,3 (Range ). Mean body length 164,69 ± 9,6 cm (Range )  Mean BMI 27,86 ± 5,8 RESULTS 28% 72%

<60 years old (n=40) ≥ 60 years old (n=60) Sex ♂ = 43 ♀ = 58 ♂ = 47 ♀ = 53 Body Length (cm) (Mean± standard desviation) 168,85 ± 9,7161,92 ± 8,5 Body weight (Kg) (Mean ± standard desviation) 79,15 ± 15,173,48 ± 16,8 BMI (Mean ± standard desviation) 27,82 ± 5,727,88 ± 5,9 RESULTS There was no statistically significant difference between both groups in body weight (p=0,088), sex (p=0,317) and body mass index (0,962).

<60 years old (n=40) ≥60 years old (n=60) Mean density Pulmonary artery (Mean ± standard desviation) 279 ± 97,3 380,4 ± 115,4 Background Noise (Mean ± standard desviation) 11,04 ± 2,210,7 ± 2,5 Signal to Noise Ratio (Mean ± standard desviation) 26,35 ± 11,438,66 ± 18,7 IMAGE QUALITY PARAMETERS RESULTS P<0,001 t - Student

RESULTS PATIENT CARACTERISTS AND IMAGE QUALITY vessel enhancement PA Age Background noise R=+0,428 R=+0,388 Patient age showed a significant positive correlation to mean vessel enhancement (r=+0,428, p>0,001) Age

RESULTS PATIENT CARACTERISTS AND IMAGE QUALITY BMI BMI showed a small but significant negative correlation to mean vessel enhancement (r=0,264, 0,008) and a moderate negative correlation to SNR (r= -0,401, p 0,001). vessel enhancement PA SNR R= -0,428 Background noise R= -0,264 R= +0,476 BMI

RESULTS SUBJETIVE IMAGE QUALITY IN MEAN PULMONARY ARTERY Subjetive image quality was comparated in both groups using Kruskall- Wallis test. Image quality was significantly higher in group A compared with the group B

DISCUSSION  CT-PA is currently regarded as the reference imaging tool in suspected PE.  Many reports have shown significant correlations between injection related-factors and vessels enhancement, including contrast volume and concentration, injection rate or type of contrast medium.  However little is known about the impact of patient characteristics.

DISCUSSION  On the basis of our study Age and BMI were the only independent factors associated with degree of enhancement in pulmonary arteries.  Significant differences are shown between young patients and old patients as regard of vessels enhancement, signal to noise ratio and subjetive image quality  Therefore, to achieve a consistent degree of contrast enhancement it would be necessary to adjust the amount of contrast medium according to the patient´s BMI and establish new strategies in young patients

 The patients in our study, groups were examined using a peripheral line that had already been placed by the referring physician. Thus, we have only limited influence on the selection of the different sides of venous access.  We evaluated patients in different hemodynamic conditions. This fact could have affect the time to reach the predefined threshold.  Although BMI is easy to recorded, it is limited in characterizing obesity because it does not distinguish between muscle and fat. DISCUSSION

CONCLUSION  On the basis of our study results, higher patient age is associated with better pulmonary contrast enhancement.  The degree of vessels contrast enhancement in CT- PA declines with increases in BMI and decreases patient age.

 This findings may be interpretated and used in clinical practice as follows: To achieve a consistent vessel enhancement, the amount of contrast should be adjusted according to the patient BMI and new strategies must be established in young patient. CONCLUSION

REFERENCES 1.Bae KT, Tao C. Gurel S. et al. Effect of patient weight and scanning duration on contrast enhancement durig pulmonary multidetector CT angyography. Radiology 2007;242: Arakawa H, Kohno T, Hiki T et al. CT pulmonary angiography and CT venography: factors associated with vessel enhancement. 3.Roggenland D, Peters S, Lemburg S. CT angiography in suspected pulmonary embolism: Impact of patient characteristics and different venous lines on vessels enhancement and image 4.Bae KT. Test-bolus traching versus bolus trach¡king technike for CT angiography timing. Radiology 2005; 236: ; 5.Kormano M. Partanen, K Somakallio S, Kivimaki T. Dynamic contrast enhancement of the upper abdomen: effect of contrast medium and body weight. Invest Radiol 1983;18: Schoellnast H, Deutschmann HA et al. MDCT Angiography of the pulmonary arteries: influence of body weigh, body mass indez, and scan length on arterial enhancement at different iodine flow rates 7.Wu A, Pezzullo J, Cronan J et all. CT Pulmonary Angiography: Quantification of Pulmonary Embolus as a Predictor of Patient Outcome. Initial Experience. Radiology 2004; 230: