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Peripheral Pulmonary Arteries: How Far in the Lung Does Multi-Detector Row Spiral CT Allow Analysis?¹

¹ From the Department of Radiology, University Center Hospital Calmette, Blvd Jules Leclerc, 59037 Lille Cedex, France (B.G., D.S., I.M., J.R., M.R.J.); the Department of Medical Statistics, University of Lille, France (V.D., A.D.); and the Medical Research Group, Lille, France (I.M., J.R., M.R.J.). From the 2000 RSNA scientific assembly. Received July 31, 2000; revision requested September 9; final revision received December 27; accepted January 11, 2001. Address correspondence to M.R.J. (e-mail: mremy-jardin@chru-lille.fr).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To analyze the influence of multi–detector row spiral computed tomography (CT) on identification of peripheral pulmonary arteries.

MATERIALS AND METHODS: Peripheral pulmonary arteries were analyzed on optimally opacified contrast material–enhanced spiral CT angiograms in 30 patients devoid of pleuroparenchymal disease who underwent scanning with multi–detector row CT (collimation, 4 x 1 mm; pitch, 1.7–2.0; scanning time, 0.5 second). Two series of scans were systematically generated from each data set, 1.25-mm-thick (group 1) and 3-mm-thick (group 2) sections, leading to the analysis of 600 segmental (20 arteries per patient), 1,200 subsegmental (40 arteries per patient), 2,400 fifth-order (80 arteries per patient), and 4,800 sixth-order (160 arteries per patient) pulmonary arteries in each group.

RESULTS: Multi–detector row CT with reconstructed scans of 1.25-mm-thick sections (group 1) allowed (a) analysis of a significantly higher percentage of subsegmental arteries (94% in group 1 vs 82% in group 2; P < .001) and (b) a significantly higher percentage of fifth- and sixth-order arteries, respectively, identified in 74% and 35% of cases in group 1 and 47% and 16% in group 2 (P < .001). The causes for inadequate depiction of subsegmental branches in group 1 were partial volume effect (43%), anatomic variants (39%), and cardiac (17%) and respiratory (1%) motion artifacts.

CONCLUSION: Multi–detector row CT with reconstructed scans of 1.25-mm-thick sections enables accurate analysis of peripheral pulmonary arteries down to the fifth order on spiral CT angiograms.

Index terms: Computed tomography (CT), angiography, 944.12916 • Computed tomography (CT), technology, 944.12915, 944.12916, 944.12919 • Embolism, pulmonary, 944.77 • Lung, anatomy, 60.12115, 60.92 • Pulmonary arteries, CT, 944.12915, 944.12916, 944.12919

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
In the early 1990s, the introduction of spiral computed tomographic (CT) technology dramatically modified the evaluation of pulmonary arteries in routine clinical practice, which was previously based either on a noninvasive but indirect method, that is, ventilation-perfusion scintigraphy, or on an invasive and underused study, that is, pulmonary angiography. As a minimally invasive examination, spiral CT angiography rapidly emerged as a potentially useful diagnostic method, enabling a direct insight into endovascular abnormalities and thus a direct depiction of endoluminal clots (1–9).

Since its introduction, spiral CT technology has progressively improved and subsequently influenced the overall accuracy of spiral CT angiography in the diagnostic work-up of pulmonary embolism. Initially performed with 5-mm collimation and 1-second rotation time, spiral CT angiography limited the detection of endoluminal clots to the segmental arteries (1–9). The availability of subsecond scanning then offered the possibility to improve longitudinal spatial resolution, previously not accessible in practical scanning times.

In an anatomic study, Remy-Jardin et al (10,11) demonstrated that scanning with 2-mm collimation at 0.75 second per revolution enabled marked improvement in the analysis of segmental and subsegmental arteries, results further confirmed in routine clinical practice. In a similarly designed study, Schoepf et al (12) also recently reported that detailed visualization of peripheral pulmonary arteries could be attained with subsecond spiral CT.

The recent introduction of multi–detector row spiral CT offers further increase in performance, in particular the ability to scan larger anatomic volumes with high spatial resolution. The purpose of this study was to analyze the influence of multi–detector row spiral CT technology on the identification of peripheral pulmonary arteries.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Population
This study was based on a retrospective analysis of spiral CT scans obtained at routine clinical practice during a 3-month period from January to March 2000. During this period, spiral CT angiograms of the pulmonary circulation were routinely obtained with a four–detector row CT scanner by using narrow collimation scanning. We selected scans in 30 patients from the 130 patients who underwent spiral CT angiography of the pulmonary circulation during this period.

To be included in the present study, spiral CT examinations had to meet the anatomic and technical criteria proposed by Remy-Jardin et al (10): (a) depiction of a complete nondilated pulmonary arterial bed in both lungs, which implied (i) the absence of a history of lung surgery, (ii) the absence of lung distortion and/or parenchymal infiltration, and (iii) the absence of patent or suspicion of primary or secondary pulmonary hypertension; (b) a technically acceptable spiral CT examination with contrast enhancement that comprised (i) acquisition during strict inspiratory apnea, (ii) a degree of arterial enhancement coded as "excellent" (high degree of vascular opacification) or "good" (degree of contrast enhancement not high but sufficient for the analysis of pulmonary arteries) from the top to the bottom of the area of interest, and (iii) absence of endoluminal and/or periluminal abnormality. CT scans in the first 30 patients who fulfilled these criteria were included in the study; these examinations were selected by the senior author (M.R.J.).

The study population comprised 18 men and 12 women (age range, 25–63 years; mean age, 48.6 years ± 15 [SD]). The indications for CT were as follows: (a) suspicion of acute pulmonary embolism (n = 11); (b) assessment of lung nodules (n = 11), including suspicion of malignant lesions and pulmonary vascular malformations; (c) cause of mild hemoptysis (n = 5), that is, hemoptysis of less than 50 mL/day; and (d) suspicion of hilar and/or mediastinal adenopathy (n = 3). In all cases, the diagnosis of pulmonary embolism was excluded on the basis of one or more of the following: a negative spiral CT scan (n = 11), a normal ventilation-perfusion scan (n = 7), or an alternative diagnosis (n = 4). In the remaining 19 patients, the final diagnoses were (a) presence of a solitary pulmonary nodule (n = 5) and normal lung parenchyma (n = 6) in the 11 patients referred because they were suspected of having lung nodules; the small size (<5 mm) of the lung nodules and their subpleural location did not affect the analysis of peripheral pulmonary vessels; (b) chronic obstructive lung disease and airway infection in the five patients examined for mild hemoptysis; and (c) absence of adenopathy in the three patients suspected of having a hilar and/or mediastinal abnormality.

CT Evaluation
Spiral CT evaluation of the pulmonary circulation was performed with a multi–detector row spiral CT scanner (Volume Zoom; Siemens, Forcheim, Germany) by using 4 x 1-mm collimation, a table speed of 7 mm (n = 19) per rotation (ie, pitch, 1.7) or 8 mm (n = 11) per rotation (ie, pitch, 2.0), and a 0.5-second rotation time (140 kV and 20–100 mAs per image, according to the indication and patient body type). From each data set, two series of transverse CT scans were reconstructed as further detailed. The scanning protocol included the survey of the entire thorax with simultaneous administration of a 24%–30% contrast material. The mean duration of data acquisition was 16 seconds (range, 9–22 seconds), and the mean z-axis coverage was 198 mm (range, 130–308 mm). Data were systematically obtained in the craniocaudal direction, from the lung apices to the level of the posterior costophrenic angles.

The patients received an injection of 120 (n = 15) or 140 mL (n = 15) of 24% ioversol (Optiray 240; Guerbet, Roissy, France) or iohexol (Omnipaque 240; Nycomed Ingenor, Amersham, United Kingdom) (n = 26) or 30% iohexol (Omnipaque 300; Nycomed Ingenor) (n = 4). The iodinated contrast material was injected by way of peripheral venous access at a rate of 4 mL/sec (n = 30); the mean start delay was 18 seconds (range, 15–28 seconds). The bolus injection technique was used to administer contrast material with an automated injector (CT 9000; Liebel-Flarsheim, Cincinnati, Ohio) in every case. The injection of contrast material was carefully monitored by a physician. Contrast material was administered with the patient’s arm alongside the thorax, which thus allowed physician control of the venous access during the injection and avoided venous compression at the thoracobrachial junction. All patients underwent scanning in the supine position.

To evaluate the influence of section thickness on the analysis of peripheral pulmonary arteries (arteries beyond the lobar level), two series of transverse CT scans were reconstructed from each data set, which led to the definition of two groups of images. Group 1 consisted of reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals; group 2 consisted of reconstructed scans of 3-mm-thick sections obtained every 2 mm. In groups 1 and 2, two series of images were systematically considered: (a) mediastinal images, reconstructed with a soft reconstruction kernel and viewed at mediastinal window settings (window width, 350 HU; window center, 50 HU); and (b) lung images, reconstructed with a high-spatial-frequency algorithm and viewed at lung window settings (window width, 1,600 HU; window center, -600 HU). The mean number of mediastinal images generated per patient was 198 (range, 130–308) in group 1 and 99 (range, 65–154) in group 2.

Because our objective was to determine whether a 1.25-mm or a 3-mm section thickness is optimal for the evaluation of subsegmental pulmonary arteries, we systematically reconstructed two section widths from each data set. The section widths were chosen to allow comparison between the results of the present study with multi–detector row spiral CT and those of previous protocols based on single-section spiral CT. The section width of the reconstructed scans in group 2, that is, 3 mm, was close to the thinnest effective section thickness evaluated in the literature at the time this article was written, that is, 2.65 mm in scans with a 2-mm collimation and a pitch of 2.0 in the study by Remy-Jardin et al (10). The second section width, that is, 1.25 mm in group 1, represented a narrower thickness that was expected to minimize partial volume effects on peripheral pulmonary arteries.

Study Design
Consensus interpretation of the CT images was performed by two radiologists (B.G., D.S.), both experienced in the reading of helical CT angiograms of the pulmonary circulation (5 years of experience), who read the images together. We did not attempt to blind the readers to the scanning technique because of obvious differences in the number of images in the two groups. The two readers analyzed group 2 images in random order. Several weeks later, they analyzed group 1 images, also presented in random order.

To identify segmental and subsegmental arteries, we used the nomenclature outlined by Remy-Jardin et al (10). This nomenclature is based on the standard descriptions by Jackson and Huber (13) and Boyden (14), with slight modifications to account for anatomic variations and the orientation of vessels in the transverse plane on CT scans (Table 1). Twenty segmental (ie, third-order) and 40 subsegmental (ie, fourth-order) arteries are described in this nomenclature. The fifth-order pulmonary arteries (n = 80) were recognized as symmetric dichotomous divisions of the corresponding subsegmental branch. The sixth-order pulmonary arteries (n = 160) were recognized as dichotomous divisions of the corresponding fifth-order pulmonary artery. To identify pulmonary arterial sections with confidence, we analyzed lung and mediastinal images simultaneously. Prior to image analysis, a training session (the 30 patient scans were not used for the training session) was held during which the readers were familiarized with the modifications in nomenclature and agreed on the following strategy for the analysis.

Statistical Analysis
The statistical analyses were performed with commercially available software (SAS; SAS Institute, Cary, NC). Each artery was individually coded as analyzable or not, leading the readers to determine a number of arteries analyzable per patient in each anatomic zone of each lung. These results were also presented as rates of recognition of pulmonary arteries, expressed as percentages and calculated by means of the following formula: The rate of recognition equalled the number of arteries coded as analyzable in a given anatomic region multiplied by 100 and divided by the maximum number of arteries anatomically present. For each category of pulmonary arteries, the distribution of rates was compared between groups 1 and 2 by using the paired Wilcoxon rank sum test, which is adapted to ordinal variables.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Analysis of Segmental Arteries (Third-Order Arteries)
The two readers analyzed 600 segmental arteries in group 1 and 600 segmental arteries in group 2 (20 segmental arteries per patient). No statistically significant difference was found in the total number of analyzable segmental arteries in groups 1 and 2, regardless of whether the left and right lung were considered together or separately. The percentages of analyzable segmental arteries were 88.5% (531 of 600 segmental arteries) in group 1 and 88% (528 of 600 segmental arteries) in group 2. The percentages of analyzable segmental arteries according to anatomic region are summarized in Table 2. Anatomic variants accounted for inadequate depiction of segmental arteries in every nonanalyzable artery in group 1 (100%) and in 69 (96%) of the 72 nonanalyzable segmental arteries in group 2 (Table 3).

View larger version (105K): [in this window] [in a new window] [Download PPT slide]   Figure 1a. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 1b. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

View larger version (95K): [in this window] [in a new window] [Download PPT slide]   Figure 1c. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

View larger version (82K): [in this window] [in a new window] [Download PPT slide]   Figure 1d. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 1e. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

View larger version (90K): [in this window] [in a new window] [Download PPT slide]   Figure 1f. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 1g. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

View larger version (90K): [in this window] [in a new window] [Download PPT slide]   Figure 1h. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

View larger version (88K): [in this window] [in a new window] [Download PPT slide]   Figure 1i. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the right middle lobe in a 63-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict subsegmental pulmonary arteries. (a-e) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (f-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-e (mediastinal images displayed in a cephalocaudal direction). The superior subsegmental ramus (RA5a; arrow) of the medial segmental artery of the right middle lobe (star) is adequately depicted on reconstructed images of 1.25-mm-thick sections, whereas it is coded as nonanalyzable on reconstructed images of 3-mm-thick sections owing to partial volume effect in its medial portion. Note the adequate depiction of the inferior subsegmental ramus (RA5b; arrowhead) on both series of images.

On group 1 scans, the frequency of identification of subsegmental pulmonary arteries was 90%–100% for all but six subsegmental arteries, namely RA2a (60%) and RA3b (87%) in the upper lobes; RA4b (87%) and LA5b (70%) in the right middle lobe and lingula; and LA7a (87%) and LA9a (87%) in the lower lobes.

The causes of inadequate depiction of subsegmental arteries are summarized in Table 3 and were related to partial volume effects in 75% of cases on group 2 scans and to partial volume effects and anatomic variants in 43% and 39%, respectively, on group 1 scans.

Analysis of Fifth- and Sixth-Order Pulmonary Arteries
A total of 2,400 fifth-order (80 arteries per patient) and 4,800 sixth-order (160 arteries per patient) pulmonary arteries were individually analyzed in each group. The frequency of identification of fifth- and sixth-order pulmonary arteries is summarized in Table 5. The percentage of analyzable fifth-order pulmonary arteries was significantly higher in group 1 (74%; 1,782 of 2,400 arteries) than in group 2 (47%; 1,128 of 2,400 arteries; P < .001) (Fig 2).

View larger version (93K): [in this window] [in a new window] [Download PPT slide]   Figure 2a. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

View larger version (93K): [in this window] [in a new window] [Download PPT slide]   Figure 2b. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

View larger version (97K): [in this window] [in a new window] [Download PPT slide]   Figure 2c. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

View larger version (96K): [in this window] [in a new window] [Download PPT slide]   Figure 2d. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 2e. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

View larger version (93K): [in this window] [in a new window] [Download PPT slide]   Figure 2f. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

View larger version (92K): [in this window] [in a new window] [Download PPT slide]   Figure 2g. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

View larger version (91K): [in this window] [in a new window] [Download PPT slide]   Figure 2h. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

View larger version (84K): [in this window] [in a new window] [Download PPT slide]   Figure 2i. Multi-detector row spiral CT scans (4 x 1-mm collimation, pitch of 1.7, and administration of a 24% iodinated contrast material at a rate of 4 mL/sec) obtained at the level of the left upper lobe in a 74-year-old woman for comparison of reconstructed images of 1.25- and 3-mm-thick sections to depict fifth- and sixth-order pulmonary arteries. (a-f) Reconstructed scans of 1.25-mm-thick sections obtained at 1-mm intervals, photographed at mediastinal window settings, and displayed in a cephalocaudal direction. (g-i) Reconstructed scans of 3-mm-thick sections obtained at 2-mm intervals in the same volume of interest as that in a-f (mediastinal images displayed in a cephalocaudal direction). Note the adequate depiction of the lateral (LA2a; small open star) and anterior (LA2b; small solid star) subsegmental rami of the anterior segmental artery (large open star) in the left upper lobe on both series of mediastinal images. The anterior subsegmental ramus of LA2b gives rise to two symmetric dichotomous divisions: a lateral fifth-order branch (arrowhead) and an anterior fifth-order branch (long arrow). The anterior fifth-order branch then divides into two symmetric sixth-order branches (short arrows). All of the fifth- and sixth-order branches are analyzable on reconstructed scans of 1.25-mm-thick sections, whereas only the anterior rami are adequately depicted on reconstructed images of 3-mm-thick sections.

The percentage of analyzable sixth-order pulmonary arteries was significantly higher in group 1 (35%; 1,667 of 4,800 arteries) than in group 2 (16%; 754 of 4,800 arteries; P < .001). The percentage of identification of sixth-order pulmonary arteries was 38% (914 of 2,400) in the right lung in group 1 (vs 17% [404 of 2,400] in group 2; P < .001) and 31% (753 of 2,400) in the left lung in group 1 (vs 14.5% [350 of 2,400] in group 2; P < .001). The sixth-order pulmonary arteries identified with the highest frequency were located in the apical segment of the right lower lobe in group 1 (59% [141 of 240]) and in the posterior segment of the right lower lobe in group 2 (37% [89 of 240]). The least-identified sixth-order pulmonary arteries were located in the left paracardiac segment, both in group 1 (7% [16 of 240]) and group 2 (2% [five of 240]).

The mean z-axis coverage enabling analysis of peripheral pulmonary arteries down to the sixth order was 165 mm ± 19, extending from 11 mm ± 7.5 above the top of the aortic arch to 54 mm ± 11.5 below the level of the right inferior pulmonary vein.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
In our study, adequate depiction of segmental arteries was attained in 88.5% and 88% of the cases in groups 1 and 2, respectively. These findings confirm previously reported results, considering anatomic and clinical studies (10–12), that showed that the mean percentage of analyzable segmental arteries was 83%–95%. In the present investigation, we specifically recorded the causes of inadequate depiction of pulmonary arteries. This led us to observe that the percentage of adequately depicted segmental arteries could reach 100% in group 1 and 96% in group 2, inasmuch as the lack of depiction of arteries due to anatomic variants can be considered within the normal range. Therefore, a technically adequate multi–detector row spiral CT angiogram is compatible with the analysis of the entire segmental arterial bed on thin-collimated scans.

A significant difference between groups 1 and 2 concerned the evaluation of the subsegmental pulmonary arteries. On group 1 scans, 94% of these arteries were adequately depicted, whereas 82% were coded as analyzable on group 2 scans. The frequency of identification of subsegmental branches was 90%–100% for all but six subsegmental arteries on group 1 scans, whereas only half of the subsegmental arteries were seen with a frequency of 90%–100% in group 2. The main reason for coding these vessels as nonanalyzable was the presence of partial volume effects, more frequent in group 2 (75% of cases [165 of 219 arteries]) than in group 1 (43% of cases [32 of 75 arteries]).

On both series of reconstructed scans, the frequency of identification of subsegmental arteries was superior to that previously reported with single-section spiral CT (10,12). Remy-Jardin et al (10) found that 37% of the subsegmental bed was analyzable on collimated scans of 3-mm-thick sections, whereas this percentage reached 61% on collimated scans of 2-mm-thick sections. Comparing spiral CT and electron-beam CT on collimated scans of 5-mm-thick sections, Schoepf et al (12) recently reported that the percentages of analyzable subsegmental arteries were 73% in the right lung and 70% in the left lung. The usefulness of narrow-collimation scanning for the analysis of subsegmental branches has also been recently underlined by Baile et al (15) in an experimental study based on single-section spiral CT.

The improvement in the evaluation of an anatomic compartment composed of branches 2–3 mm in diameter is directly related to the availability of multi–detector row spiral CT scanners, enabling scanning of the pulmonary vascular bed with a narrow collimation during acceptable scanning times, otherwise shorter than those commonly selected with single-section spiral CT. In the present study, our population underwent scanning with a four–detector row spiral CT scanner with a 0.5-second rotation time. The mean duration of data acquisition for the entire thorax was 16 seconds, whereas it was 26 seconds in the study by Schoepf et al (12) and 22 seconds for the coverage of a 10–12-cm region of interest in the study by Remy-Jardin et al (10).

As small arterial branches were easily depicted on narrowly collimated scans in routine clinical practice, we attempted to determine the frequency of identification of the fifth- and sixth-order arteries with multi–detector row spiral CT, which was previously not investigated in the radiology literature, to our knowledge. We observed that 74% of the fifth-order pulmonary arteries were analyzable in group 1, a percentage significantly higher than that found in group 2 (47%). As expected, the percentage of analyzable sixth-order pulmonary arteries was significantly higher in group 1 (35%) than in group 2 (16%). Despite an overall limited identification of these branches on narrowly collimated scans, it is noticeable that sixth-order pulmonary branches could be identified in 59% of cases in the apical segment of the right lower lobe in group 1 and in 37% of cases in the posterior segment of the right lower lobe in group 2. Obviously, multi–detector row spiral CT does not allow the evaluation of pulmonary arteries down to the capillary bed as on conventional or digital angiograms. However, our results suggest that the fifth- and sixth-order pulmonary arteries should no longer be considered beyond the scope of CT evaluation when scanning with subsecond multi–detector row spiral CT.

Because our investigation was performed in optimal conditions, namely the analysis of a complete nondilated pulmonary arterial bed in both lungs on technically optimal spiral CT examinations, these results need further validation in clinical studies. However, conversely to the anatomic studies (10,12) previously published, the present study did not compare scans from different populations. Therefore, differences observed between the two groups of patients in our study were not influenced by differences in arterial patterns but reflected technical differences between CT scans.

Because the main goal of the present investigation was to determine whether an accurate analysis of subsegmental and smaller branches could be performed with multi–detector row CT, the consensus reading of two experienced chest radiologists was considered to be better suited to this anatomic study. Therefore, we did not attempt to evaluate interobserver variability in the recognition of peripheral pulmonary arteries. From a practical standpoint, the analysis of peripheral pulmonary arteries on hard copies was judged time-consuming by the two readers, especially for the reconstructed scans of 1.25-mm-thick sections. Further studies are needed to establish whether these vessels can be accurately depicted alternatively with diagnostic workstations.

Our results demonstrate that peripheral pulmonary arteries down to the fifth-order branches can be accurately depicted with reconstructed scans of 1.25-mm-thick sections by using multi–detector row spiral CT. The ability to scan the entire thorax with narrow collimation is expected to modify the imaging protocol of the pulmonary circulation in routine clinical practice, as well as the radiologist’s daily approach to viewing the number of images generated from each data set.

	FOOTNOTES

 
Author contributions: Guarantors of integrity of entire study, M.R.J., J.R.; study concepts and design, M.R.J., B.G.; literature research, M.R.J., J.R.; clinical studies, M.R.J., J.R., I.M.; data acquisition, M.R.J., D.S., B.G.; data analysis/interpretation, D.S., B.G.; statistical analysis, V.D., A.D.; manuscript preparation, M.R.J.; manuscript definition of intellectual content, M.R.J., J.R.; manuscript editing, M.R.J.; manuscript revision/review, M.R.J., B.G.; manuscript final version approval, J.R.

	REFERENCES

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