Introduction
Methods to minimize dose
Dose related issues
Limiting craniocaudal coverage length
Tube amperage
Dose modulation (electrocardiographic pulsing)
Scanner type
Reducing tube voltage
Dose reduction technique | Effectively lowers exposure with retrospective gating | Estimated dose reduction for retrospective | Effectively lowers exposure with prospective triggering |
---|---|---|---|
Scan length | ↓↓↓ | Proportional | ↓ |
Adding calcium Score to lower scan length | ↓↓ | 30% | ↑ |
Reducing amperage (mA) | ↓ | Proportional | ↓ |
Dose modulation | ↓↓↓ | 20–40% | Not applicable |
Reducing tube voltage to 100 kVp | ↓↓↓ | 40% | ↓↓↓ |
Limiting scan field of view | ↓↓↓ | 67% | ↓↓ |
Limiting field of view (Fov)
BMI | Calcium scan | Retrospective | KvP | DLP | Estimated mSv including CAC scan | ||||
---|---|---|---|---|---|---|---|---|---|
kVp | mA | Max mA | Min mA | ||||||
19 and less | 250 | 120 | 300 | 280 | 140 | 100 | C2/Small filte | 244 | 4.148 |
20–22 | 275 | 120 | 350 | 325 | 170 | 100 | C2/Small filte | 289 | 4.913 |
23–25 | 300 | 120 | 375 | 350 | 190 | 100 | C2/Small filte | 311 | 5.287 |
26–28 | 325 | 120 | 450 | 425 | 215 | 100 | C2/Small filte | 359 | 6.103 |
29–31 | 350 | 120 | 500 | 475 | 240 | 120 | C2/Small filte | 640 | 10.88 |
32–35 | 375 | 120 | 600 | 575 | 290 | 120 | C2/Small filte | 772 | 13.124 |
36–37 | 400 | 120 | 700 | 650 | 290 | 120 | C3/Med filter | 954 | 16.218 |
≥38 | 425 | 120 | 800 | 750 | 375 | 120 | C3/Med filter | 1,170 | 19.89 |
>40 | 450 | 120 | 800 | 775 | 388 | 120 | C3/Med filter | 1,270 | 21.59 |
Sequential (prospective) scanning versus retrospective gating
Action | Parameter |
---|---|
Cardiac mode | Prospective step-and-shoot (SnapShot Pulse) |
Rotation time | 0.35 s |
Start location and end location | Based on scout coverage—base of the heart to apex (about 1 cm above the left main artery to about 1 cm below the posterior descending artery) |
Detector coverage | 40 mm |
Slice thickness | 0.625 mm |
Padding | Set by system or turned off |
SFOV (scan field of view) | Small or medium depending on the body habitus of the patient |
DFOV | Typically 18 or 15 cm field of view to include all of the cardiac structures |
kVp | 120 kVp ≥ 85 kg patient (obese or morbidly obese) |
100 kVp for < 85 kg patient | |
mA | 350—Small patient |
450—Medium patient | |
550+ —Large patient |