CT Angiography in Patients with Peripheral Arterial Disease

Rationale and Objectives

We investigated the effects of small focal spot (SFS) imaging and iterative model reconstruction (IMR) on the image quality of computed tomography angiographs (CTA) in patients with peripheral arterial disease.

Materials and Methods

We divided 60 consecutive patients with suspected or confirmed peripheral artery disease into two equal groups. One group underwent large focal spot scanning under our standard CTA protocol with hybrid iterative reconstruction (iDose 4 ) (protocol 1), and the other underwent scanning with the SFS protocol and IMR (protocol 2). Quantitative image quality parameters, ie, arterial computed tomography attenuation, image noise, and the contrast-to-noise ratio, were compared and the visual image quality (depiction of each vessel) was scored on a 5-point scale.

Results

There was no significant difference in the arterial attenuation among all evaluated slice levels. The mean image noise was significantly lower under protocol 2 and the contrast-to-noise ratio was significantly higher at all slice levels. The visual scores assigned to the two protocols for the depiction of large vessels, such as the abdominal aorta and iliac artery, were comparable. However, the mean visual scores for small vessels in the lower extremities were significantly higher under protocol 2.

Conclusion

CTA with SFS and IMR yielded significantly better qualitative and quantitative image quality especially for small vessels.

Introduction

Peripheral artery disease (PAD) is a common, chronic, progressive health problem . It affects up to 8.5 million (7.2%) Americans in their 40s and is associated with significant morbidity and mortality . The 5-, 10-, and 15-year morbidity and mortality rates from all causes in patients with PAD are approximately 30%, 50%, and 70%, respectively. Coronary artery disease is the most common cause of death amongpatients with PAD (40%–60%); cerebral artery disease accounts for 10%–20% of deaths . Early diagnosis and appropriate medical intervention can mitigate limb-specific symptoms, improve the quality of life, and decrease systemic cardiovascular risks .

Digital subtraction angiography (DSA) is considered the reference standard for diagnosing PAD. However, it is invasive and carries limitations and risks . Computed tomography angiography (CTA), a less invasive and safer examination, is an alternative to DSA and has gained widespread clinical acceptance for diagnosing PAD . Although CTA of lower extremities is more sensitive, specific, and accurate for assessing the location and extent of peripheral artery stenosis than DSA , its spatial resolution is inferior to DSA, and the visualization of small vessels, such as the peripheral small artery and collateral vessels, is suboptimal.

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Materials and Methods

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Study Population

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Table 1

Patient Demographics

LFS Protocol ( n = 30) (Protocol 1) SFS Protocol ( n = 30) (Protocol 2)P Value Sex (male/female) 21/9 20/10 0.72 Age (y) 72.8 ± 8.6 74.1 ± 9.3 0.55 Body height (cm) 157.6 ± 7.9 158.9 ± 8.3 0.53 Body weight (kg) 61.2 ± 13.0 59.7 ± 15.9 0.70 Body mass index (kg/m 2 ) 24.5 ± 4.3 23.4 ± 4.6 0.34 eGFR (mL/min/1.73 m 2 ) 33.1 ± 30.4 32.5 ± 30.8 0.94

eGFR, estimated glomerular filtration rate; LFS, large focal spot; SFS, small focal spot.

Note: Data are mean ± standard deviation.

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CT Scanning and Contrast Infusion Protocols

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Table 2

Imaging and Contrast Material Parameters of the LFS and the SFS Protocols

LFS Protocol (Protocol 1) SFS Protocol (Protocol 2) CT scanner 256-slice CT (Brilliance iCT, Philips Healthcare) Collimation 128 × 0.625 mm Tube voltage 100 kVp Effective tube current 231 eff. mAs (reference) with auto-modulation Rotation time 0.75 s/rot Helical pitch 0.585 Total amount of contrast medium 500 mgI/mL Injection duration 25 s Bolus tracking trigger 150 HU (abdominal aorta) Scan delay 15 s Image reconstruction iDose 4 IMR Section thickness/interval 1.0/0.5 mm

CT, computed tomography; IMR, iterative model reconstruction; LFS, large focal spot; SFS, small focal spot.

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CT Image Reconstruction

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Quantitative Image Quality Analysis

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CNR=(HUA−HUM)/image noise, CNR

=

(

HU

A

−

HU

M

)

/

image noise

,

where HU A and HU M are the CT attenuation in the artery and muscle, respectively, and HU M is the CT attenuation in the muscle. These parameters were compared in protocols 1 and 2.

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Qualitative Image Quality Analysis

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CT Radiation Dose

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Statistical Analysis

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Results

Quantitative Image Quality Analysis

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Qualitative Image Quality Analysis

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Table 3

Qualitative Assessment of Image Quality

LFS Protocol (Protocol 1) SFS Protocol (Protocol 2)P Value Abdominal aorta 4.9 ± 0.3 5.0 ± 0.0 0.51 Renal artery 4.4 ± 0.8 4.7 ± 0.6 0.08 Common-external iliac artery 4.7 ± 0.5 4.9 ± 0.2 0.08 Internal iliac artery 4.2 ± 0.6 4.7 ± 0.5 <0.01 Superior-inferior gluteal artery 3.4 ± 0.6 4.2 ± 0.7 <0.01 Superficial femoral artery-popliteal artery 4.3 ± 0.5 4.8 ± 0.4 <0.01 Deep femoral artery 4.2 ± 0.6 4.8 ± 0.4 <0.01 Descending branch of the lateral femoral circumflex artery 3.7 ± 0.4 4.4 ± 0.7 <0.01 Descending genicular artery 3.6 ± 0.6 4.5 ± 0.7 <0.01 Tibial artery 3.8 ± 0.7 4.3 ± 0.8 <0.01 Dorsalis pedis artery 3.5 ± 0.7 4.2 ± 0.7 <0.01

LFS, large focal spot; SFS, small focal spot.

Data are mean ± standard deviation.

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CT Radiation Dose

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Discussion

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