The adjustment of radiation dose in many CT protocol are based on body mass index(BMI) or weight of the patient.

In the literature, neck circumference (NC) has been reported as a new anthropometric parameter indicating the body mass for the upper body.

NC may be an important landmark in the determination of the low dose protocols for upper body CT examinations such as neck, chest and coronary CT.

Over the last few decades, MDCT(multidetector computed tomography), cardiac imaging, CT perfusion techniques, high-pitch CT, and dual-energy CT have been introduced to clinical practice, increasing the overall amount of radiation applied. There are two types of approaches in accordance with the "as low as reasonably achievable (ALARA)" principle in MDCT. One of them is related to new technology products and different imaging techniques such as dose modulation along the x-, y-, and z-axes (anatomical tube current modulation, ECG-controlled tube current modulation or dynamically adjustable pre-patient collimation of the X-ray beam in the z-axis direction, iterative reconstruction technique. The other strategy is individualized screening-dose protocols based on body size. However the radiologist is facing the challenge of providing diagnostic image quality at the lowest radiation dose.

Body mass index (BMI) is not only the most widely used anthropometric tool for defining overweight and obesity, but it is also the most commonly reported body index for adjusting low dose in MDCT.Despite this popularity of BMI, it is becoming increasingly more clear that BMI is not a good surrogate for regional adiposity. Regional fat deposition, especially in the upper body region, is a better predictor of some obesity related complications than BMI. Accordingly, it has been reported that several anthropometric parameters of the chest might serve as a surrogate instead of BMI for individualized dose settings Neck circumference(NC) is a kind of somatometric parameter like wrist or hip circumference that reflects the upper body size. NC may be an important landmark in the determination of the low dose protocols for upper body CT examinations such as neck, chest and coronary CT. Although investigators have not encountered studies in the literature, this point will be evaluated in our study.The purpose of this study is to evaluate if NC is an appropriate and a novel parameter for adjusting and reduction of the effective chest CT radiation doses in comparison with BMI or not.

Inclusion Criteria:

• clinical diagnosis of pulmonary diseases
• participants who can be referred to radiology for diagnostic imaging
• participants who allowed to be taken somatometric measurements

Exclusion Criteria:

• participants who did not allow to be taken somatometric measurements
• participants with incomplete data (such as missing weight or height data)
• pediatric and pregnant patients