Role of different imaging modalities of vascular calcification in predicting outcomes in chronic kidney disease

Table 1 Summary of different imaging modalities for vascular calcification in chronic kidney disease

Types of X-rays	Calcification area	Advantages	Limitations	Scoring methods	Outcomes prediction
Plain radiography
Lateral lumbar spine	Abdominal aorta	Simple	Subjective quantification	Kauppila et al[5]	CV events, mortality
Postero-anterior chest	Aortic arch	Simple, readily available in almost all patients		Ogawa et al[22]	CV events, mortality
Lateral chest	Aortic arch	Simple		Noordzij et al[28]	Mortality
Antero-posterior pelvis	Iliac and femoral arteries	Simple, allow differentiation between intimal- and medial-type calcification		Adragão et al[33]	CV events, mortality
Hand	Radial, ulnar and digital arteries	Simple, allow analysis of medial-type calcification		Adragão et al[33]	Outcome data is lacking
Foot	Tibial, dorsalis pedis, plantar and digital arteries			Not available	Outcome data is lacking
Mammography	Intramammary arteries	Readily available in most women, allow analysis of medial-type calcification	Subjective quantification	Not available	PAD events
Ultrasonography	Carotid, femoral and peripheral arteries	No radiation exposure, allow evaluation of arterial wall thickness and lumen size	Only superficial arteries can be evaluated, subjective quantification	Not available	CV events, mortality
Computed tomography		Intravenous contrast is not required, the most objective and reproducible quantification which allows analysis of progression	Cost, radiation exposure, does not allow differentiation between intimal- and medial-type calcification
Chest	Coronary arteries			Agatston et al[63]	CV events, mortality
	Thoracic aorta			Callister et al[100]
Abdomen	Abdominal aorta			Hong et al[101]	CV events, mortality

CV: Cardiovascular; PAD: Peripheral arterial disease.

Table 2 Summary of scoring systems for vascular calcification in chronic kidney disease

Scoring methods	Calcification area	Details
Kauppila et al[5]	Abdominal aorta between L1-L4 in a lateral lumbar spine radiograph	The length of calcification in the anterior and posterior wall of the aorta in front of each vertebra is scored between 0-3. Total score is the sum of calcification in both walls of the aorta between L1-L4
Ogawa et al[22]	Aortic knob in a PA chest radiograph	A scale with 16 circumferences is attached to the aortic knob. The number of sections with calcification are counted
Noordzii et al[28]	Aortic arch in a lateral chest radiograph	Visual inspection of calcification. The degree of calcification is categorized into no (score 0), moderate (score 1) or severe (score 2) calcification
Adragao et al[32]	Iliac and femoral arteries in a pelvic radiograph and arteries of both hands in a bilateral hand radiograph	The pelvic radiograph is divided into four sections by a horizontal line over the top of both femoral heads and a vertical line over the vertebral column. The bilateral hand radiograph is divided by a vertical line which separates each hand and a horizontal line over the top of metacarpal bones. The presence of linear calcifications in each section is counted as 1
Agatston et al[63] (CAC score by area)	Coronary arteries in a thoracic CT scan	CT images of 3 mm thickness are acquired from the carina to the diaphragm. The calcified lesion in coronary arteries is the area of at least 0.5 mm2 that has a threshold density ≥ 130 HU. The density score 1 = 130-199 HU, 2 = 200-299 HU, 3 = 300-399 HU and 4 ≥ 400 HU. The calcification area is then multiplied by the density score
Callister et al[100]	Coronary arteries in a thoracic CT scan	Coronary calcium volume score is obtained from the multiplication of calcification area by the section thickness. A square root is applied to the volume score in order to decrease the variability among those with high scores
Hokanson et al[102] (CAC score by volume)
Hong et al[101] (Calcium mass score)	Coronary arteries in a thoracic CT scan	Measurement of the absolute mass of CaHA. The procedure uses a phantom containing different concentrations of CaHA placed beneath the thorax in order to calibrate the segmented coronary calcium. The absolute score is expressed as milligrams of CaHA
Moe et al[83]	Different portions of thoracic aorta visualized in a thoracic CT scan	The scores are based on the area calcification as described by Agatston et al or the volume calcification as described by Callister et al or Hokanson et al
Chertow et al[103]
Yildiz[104]
DeLoach[105]
Kabaya et al[106]	Abdominal aorta 10-15 cm in length above the bifurcation in abdominal CT scan	Abdominal aorta is evaluated in 10-15 CT slices at 0.8-1 cm interval. The proportion of aortic circumference covered by calcification is quantified in relation to the total circumference in each slice. The score is total calcification in all slices
Taniwaki et al[107]
Yamada et al[108] (Aortic calcification index)

CT: Computed tomography; CaHA: Calcium hydroxyapatite.