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

Why – How – Pitfalls

Why NCCT for KUB Stone?

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

Stone Types Based On CT Characteristics

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

ACR Appropriateness Criteria (2015)

ACR Appropriateness Criteria (2015)

ACR Appropriateness Criteria (2015)

Diagnostic Strategies

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

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

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

Daniels B, et al. Ann Emerg Med 2016 March

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

Stone CT Radiation Dose

Stone CT Radiation Dose: How Low Can We Go?

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

2.2 mSv

Reduced-dose CT

Initial CT

F/U CT (known stone) Can accept more noise to reduce dose

8.3 mSv

3.7 mSv

How About Giving IV Contrast?

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

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

High-density calcium stone in renal pelvis with obstruction

Advanced scanner can predict which stone is uric acid (medical) or non-uric acid

How We Interpret CT Stone Protocol

Soft tissue rim sign = ureteral stone

Stone Size and Appearance

Perinephric/periureteric Changes

Risks for Stone Formation Identifiable on Imaging

Typical Cases

hydronephrosis

stone

Distal ureteric stone with obstruction

Typical Cases

Hydronephrosis & minimal perinephric fat stranding

stone

Unilateral Perinephric Fat Stranding w/o Stone - DDx

Mimickers on CT of:

Moore CL, et al. Acad Emerg Med 2013;20:470

N=5383 Descriptive study No comparison Two EDs

Alternative Diagnosis

Incidental Findings

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

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

N=5383 Descriptive study, no comparison Two emergency departments

Take Home Messages