The document discusses the CT stone protocol, focusing on the reasons for using non-contrast CT for detecting kidney stones, the sensitivity and specificity of various imaging methods, and diagnostic strategies for assessing uncomplicated ureteral stones. It highlights the importance of stone composition, detection methods, and a proposed stone score to evaluate the probability of symptomatic stones. Additionally, it addresses radiation doses associated with CT scans and the interpretation of the imaging findings related to stone formation.

1. Hello…. CT Stone Protocol
Why, How and Pitfalls
Rathachai Kaewlai, MD
Division of Emergency Radiology, Department of Radiology
Ramathibodi Hospital, Bangkok, Thailand
For RCRT-RST Annual Scientific Meeting, 24 Mar 2016

2. Why – How – Pitfalls

3. Why NCCT for KUB Stone?

4. Virtually All KUB Stones
Are Radiopaque on CT
Composition Frequency
(%)
Radiopacity
Radiograph
Shade of
White on CT
Calcium phosphate 10 4
Calcium phosphate/
oxalate
40 3-4
Calcium oxalate 30 3
Struvite 10 2-3
Cystine 1 1
Uric acid 10 0
Genitourinary Imaging: the Requisite

5. Stone Types Based On CT
Characteristics

6. Detection of Stones
X-ray IVU Ultrasound NCCT
Sensitivity (%) 44-77 52-87 19-93 94-100
Specificity (%) 80-87 94-100 84-100 92-100

7. ACR Appropriateness Criteria (2015)

8. ACR Appropriateness Criteria (2015)

9. ACR Appropriateness Criteria (2015)

10. Diagnostic Strategies

11. Factor Definition Level Points
Sex Female
Male
0
2
Timing Duration of pain from onset
to presentation, h
>24
6-24
<6
0
1
3
Origin Race Black
Nonblack
0
3
Nausea Presence of nausea and
vomiting
None
Nausea only
Vomiting
0
1
2
Erythrocyte Hematuria on urine dip Absent
Present
0
3
Total 0-13
STONE score
for uncomplicated ureteral stone in ED
Moore CL, et al. BMJ 2014;348:g2191

12. Points
Probability of
symptomatic stone on CT
%
Recent
validation
(n=264)
0 to 5 Low 10% 10%
6 to 9 Moderate
10-90%
(~50%)
60%
10 to 13 High >90% 89%
STONE score
for uncomplicated ureteral stone in ED
Moore CL, et al. BMJ 2014;348:g2191
Moore CL, et al. Radiology 2016 March

13. STONE score Sensitivity Specificity
Low probability (n=144)
without ultrasound
with ultrasound
3
64
67
87
Moderate probability (n=411)
without ultrasound
with ultrasound
41
60
42
71
High probability (n=280)
without ultrasound
with ultrasound
55
69
91
60
Daniels B, et al. Ann Emerg Med 2016 March
STONE PLUS
for uncomplicated ureteral stone in ED

14. Daniels B, et al. Ann Emerg Med 2016 March

15. Ramathibodi Protocol (WIP) < 80 kg >/= 80 kg
kVp 100 120
mA 70-250 70-350
Rotation time (s) 0.6 0.6
SureExposure 3D 20 20
PF/HP 0.828/53 0.828/53
Slice thickness/interval (mm) 2.0/1.5 2.0/1.5

16. Stone CT Radiation Dose

17. Stone CT Radiation Dose:
How Low Can We Go?

18. Moore CL, et al. Ann Emerg Med 2015;65:189
N=201
Prospective, head-to-head comparison standard v reduced-dose CT
Two groups: BMI <30 v. BMI >30

19. 2.2 mSv
Reduced-dose CT

20. Initial CT
F/U CT (known
stone)
Can accept more
noise to reduce dose
8.3 mSv
3.7 mSv

21. How About Giving IV
Contrast?

22. Forniceal rupture with urinoma due to obstructing Lt UVJ stone
UVJ stone
Delayed nephrogram
Perinephric fluid
Urine extravasation confirmed at delayed scan
although this phase is not necessary

23. McLaughlin PD, et al. Insights Imaging 2014;5:217
5.1 mSv (ASiR)
5.1 mSv (FBP)
0.56 mSv (FBP)
0.56 mSv (40% ASiR)
0.56 mSv (70% ASiR)
0.56 mSv (90% ASiR)
CT Doses Even Lower than Abdominal Radiograph
N=33
Comparing routine
and sub-mSv CT (with
iterative recon)
Calculi >3 mm:
Sensitivity 87%,
specificity 100%
1 missed appendicitis
1 missed dermoid
Advanced
scanner can
reduce dose
further with
iterative
reconstruction

24. High-density calcium
stone in renal pelvis with
obstruction
Advanced scanner can predict which stone
is uric acid (medical) or non-uric acid

25. How We Interpret
CT Stone Protocol

26. Soft tissue rim sign = ureteral stone

27. Stone Size and Appearance

28. Perinephric/periureteric
Changes

29. Risks for Stone Formation
Identifiable on Imaging

30. Typical Cases
hydronephrosis
stone

31. Distal ureteric stone with obstruction
Typical Cases
Hydronephrosis & minimal
perinephric fat stranding
stone

32. Unilateral Perinephric Fat
Stranding w/o Stone - DDx

33. Mimickers on CT of:

34. Moore CL, et al. Acad Emerg Med 2013;20:470
N=5383
Descriptive study
No comparison
Two EDs
Alternative Diagnosis

35. Incidental Findings
Samim MM, et al. JACR 2015;12:63

36. Samim MM, et al. JACR 2015;12:63
N=5383
Descriptive study, no comparison
Two emergency departments

37. Take Home Messages