kidney stone diagnosis and managment ak et al. rsna 2010
TRANSCRIPT
HARVARD MEDICAL SCHOOL
Kidney Stone Diagnosis and Managment
Dushyant Sahani MD
Disclosures
• MGH has research agreement – GE Health Care– Siemens Medical Systems
Clinical Perspective
• Urolithiasis has a life time risk of 10-15% • It has a high relapse rate (50% in 5-10 yrs and 75% in 20 yrs)• Affects Men more than women
• Common clinical presentation – Acute flank pain and hematuria
Prevalenceof
Urolithiasis3.2%
5.2%
1970s 1990s1980s
Rising Prevalence
Curhan, G.C., Epidemiology of stone disease. Urol Clin North Am, 2007. 34(3): p. 287-93.
MDCT in Urolithiasis• Unenhanced CT - Initial investigation of choice in suspected urolithiasis
– 22% of all CT performed in the ER for acute abdomen pain
• Highly accurate test (Sensitivity = 95-98% & Specificity =96-100%)
– Detects other causes of acute flank pain
• Identification of ureterolithiasis at imaging altered management in nearly
55%–60% of patients suspected of having acute renal colic.
• Reveals associated abnormalities like congenital abnormalities,
infections and neoplasms• Rosen MP et al. Eur Radiol 2003;13(2):418–424.• Dalrymple NC et al. J Urol 1998;159(3):735–740.• Wrenn K. Ann Emerg Med 1995;26(3):304–307.
Stone Types
Calcium oxalate monohydrate (COM) & dehydrate (COD)
40-60% Radio-opaque Radio-opaque
Hydroxyapatite (Calcium phosphate)
20-60% Radio-opaque Radio-opaque
Radio-opaque Radio-opaque 2- 4%Brushite
Uric Acid Radio-opaque Radio- lucent 5-10%
Struvite 5-15% Radio-opaque Radio-opaque
Radio-opaque 1- 2.5% Mildly Opaque Cystine
Composition On KUB On CTOccurrence
Radioopacity
MDCT Technique
• Scan Coverage - Upper pole of kidneys to the base of the bladder
• Patient preparation -Bladder distension to visualize stones within the distal ureter
Coronal Reformations (2.5 - 3mm)
Slice thickness – 3-5 mmPitch - 1 - 1.6
Urolithiasis –CT Diagnostic Signs
Primary sign of Ureterolithiasis
Stone in the ureter (target sign) with proximal
hydroureter
Virtually all stones are
radio-opaque on CT (>200HU)
Stones radiolucent on CT - Pure matrix stones and stones made of pure Indinavir (Indinavir - Protease inhibitor used in the treatment of HIV)
• Improved detection of stones unrecognized on axial images
• Improved detection of small ureteral and renal calculi at poles
• Phleboliths and calcified vascular plaques from urinary stones
• Enhances radiologist confidence
• Benefits the urologists in treatment decision
1 2
Value of Coronal Reformations
Lin WC et al. J Urol 2007.
Factors Influencing Treatment Decision
Presence of obstruction is not the primary factor
considered for urologic intervention
Urologic intervention is influenced by 3 crucial factors
Stone size/ location
Stone Composition
Patient Symptoms
• Bierkens AF et al. Br J Urol. 1998.• Eisner BH et al. Urology 2008. • Phipps S et al. Ann R Coll Surg Eng 2010.
8mm 6 mm
• Accurate stone size measurement is paramount to plan treatment options
• The ideal method for accurate measurement on CT is to measure using
bone window settings (1250 X 250) and magnification
Soft tissue window Bone window with Magnification
Stone Size
• Stone burden (stone size and volume) determines the type of procedure
• ESWL or Ureteroscopy is performed for stones <1cm
•PCNL for stones >1.5cm
Stone Burden Assessment
Eisner BH et al. J Urol 2009
Stones > 6mm & <15mm(6-9 mm uereteral stone 60-25% pass)
Stone location predicts outcome Upper=48%, mid=60%, lower 75-79%
likely to pass spontaneously
Stone < 5mm (98% for stones < or = 4mm
pass spontaneously)
Medical Expulsive therapy(Alpha blockers)
Intervene for unremitting pain, nausea, fever, failure
to passage on medical therapy
• Extracorporeal Shockwave lithotripsy (ESWL)
• Ureteroscopic lithotripsy (upper ureter or larger stone)
Stone >15mm or Staghorn Calculi
Percutaneous Nephrolithotomy
(PCNL)
Stone Size & Treatment Decisions
• Bierkens AF et al. Br J Urol. 1998.• Coll DM et al. AJR 2002.• Eisner BH et al. Urology 2008. • Phipps S et al. Ann R Coll Surg Eng 2010.
• Linear measurement not suitable in irregularly contoured stones like
stag horn calculi
• Measuring the stone volume eliminates this problem
• Total stone volume is an appropriate measure of stone burden
22 cc
Stone Volumetry
Threshold based CAD Algorithms or manual semi-automated methods
• Demehri S et al. AJR 2012.• Singh Ak et al. RSNA 2010.
Independent Variables
(Dependent Variable= failure
rate)
Area-Under Curve (AUC)
Cut-off value Sensitivity; Specificity (%)
95% Confidence
Interval (CI)
P=value
Stone Volume CAD 0.895 >712.54 mm3 80;80 0.745-0.964 P<0.0001
Stone Volume-Products
0.872 >564.75 mm3 88;73 0.728-0.956 P<0.0001
Maximum Stone Size
0.839 >8.89mm 96;60 0.688-0.936 P<0.0001
Number of Stones 0.755 >2 52;86 0.593-0.877 P=0.0002
Mean Stone Size 0.735 >6.25mm 92;46.7 0.571-0.861 P=0.0002
Age 0.524 <50y 96;33 0.360-0.684 P=8267
Overall model fit (Chi square)=21.818; p=0.0006
ESWL Failure: Multivariate CT characteristics
Singh Ak et al. RSNA 2010.
<400 HU
Uric Acid Stone
Medical ManagementAllopurinol
Treatment of Hyperuricemia
<1000 HU(Struvite)
ESWL
>1000HU (Brushite, Cystine, COM)
UreteroscopyPCNL
Stone Composition & Treatment Decisions
> 500 HU
Hamm M et al. J Urol 2002.Parker BD et al. Urology 2004
MDCT and Stone CompositionStone composition can be determined using HU
CT Attenuation values – 64-77% accuracy in determination of stone
composition, is not robust and reliable
Stone Composition Attenuation value at 120kVp
Uric Acid 200-450 HU
Struvite 600-900 HU
Cystine 600-1100 HU
Calcium Phosphate 1200-1600 HU
COM and Brushite 1700-2800 HU
• Stone composition also effects the efficacy of ESWL (Brushite, cystine and
COM stones are hard and resistant, while struvite stones usually fragment easily)
Dretler SP. J Endourol 2001Motley G et al. Urol 2001Eisner BH et al. J Urol 2009KulkarniN et al. JCAT (in-press)
Uric Acid Stone Non uric acid stone
Element composition Light Elements(H, C, N, O)
Heavy Elements(P, Ca, S)
Attenuation at 80 kVp Lower HU Higher HU
Attenuation at 140 kVp Higher HU Lower HU
80kV
Calcium710 HU
Uric Acid290 HU
140kV
Calcium480 HU Uric Acid
315 HU
DECT: Stone composition
Renal Stone Composition: 11 studies (dsDECT=8 & ssDECT=3)
• Uric Acid vs. Non UA stone differentiation possible– Phantom and humans 100% – Reliable for stones 3 mm and above
• Non-UA subtype of pure composition possible in phantom and in humans – mixed composition stones difficult to characterize
Stolzman P. Urol Res 2008, Graser A. Invest Radiol 2008, Matlaga B. Urology 2008, Graser A . Eur Radiol 2009, Thomas C. Eur Radiol 2009, Ball D. Radiology 2009,, Hidas G. Radiology 2010, Manglaviti G. AJR 2011, Kulkarni N. JCAT (in-press)
Stone Fragility in Guiding Treatment
• CT helps predict stone fragility and susceptibility to lithotripsy
• Stones which are heterogeneous are more fragile than homogenous
stones which are more resistant to ESWL
HeterogenousMore fragile toLithotripsy
HomogenousMore resistantto lithotripsy
Stone Precursor-Randall’s Plaque
Normal papillae
Stone bearing papillae
30 HU
58 HU
• Randall’s Plaque - Calcium salt deposits
in the tip of renal papilla of patients with
nephrolithiasis and are potential sites for
calculus formation
• These stone bearing papillae appear
denser on non-contrast CT and represent
Randall’s plaque on endoscopy
• MDCT can help select patients at high-
risk for stone formation, who may
undergo appropriate medical
management to halt the formation of
stones
Whitish deposits- Randall’s plaque
Eisner BH et al. J Endourol 2008
MDCT in Planning Intervention
• Simple trigonometry on CT of the patients with complex stones could help
endourologists in planning renal access.
• CT also helps in planning surgical interventions by identifying the location of the
posterior calyx thus guiding fluoroscopic procedures like percutaneous
nephrolithotomy
Calculi with attenuation > 300 HU are radio-opaque & are followed up by Abdominal Radiograph
Calculi with attenuation < 200 HU are radiolucent & hence followed up by CT
>300 HU Follow up Radiograph <200 HU Follow up CT
In patients managed medically,
CT attenuation is a good predictor of utility of radiography in routine follow up
Stone Follow up
Pre Treatment Post Treatment
Significant Stone Burden Residual Stone Burden though significantly reduced
Significant stone burden necessitates further treatment
Stone Follow up –Post Intervention
• Differentiation between stent and stone is vital in post surgical follow up
• Stents and stones have the same CT appearance on abdominal window.
• Bone window allows visual distinction between the stent and the stone
which is accounted for by differences in pixel density.
Stones
Stent
Bone windowAbdominal window
Stone vs Stent
Tanricut C et al. Urology 2004
• A key concern for repeated CT examinations in recurrent stone disease.
• The effective radiation dose during unenhanced CT
2.8 to 13.1 mSv for men / 4.5 to 18 mSv for women
• Techniques for Reduction of Radiation dose
- Limit scanning area (not typical Abd+Pelvis exam)
- Increase in axial slice thickness to 5mm from 1-3 mm
and include 2.5-3 mm coronal reconstructions
- Lower dose CT exam ( noise index, kVp, pitch)
MDCT and Radiation Dose
Strategies for Dose ReductionLimit
Scanning area
+Low mAs
+Low kVp+
Increase slice thicknessInclude coronal reformations
DLP 1000 mGy-cm
Total Dose Reduction by 40-70% from Standard dose
DLP 200 mGy-cm
Renal stone
Initial scan – Standard dose CT (low mAs)
Follow up scan – ultra-low dose CT
Ultra-low dose approaches
WT kVp mA
Low dose CT <200 lbs 80 75-150
> 200 lbs 100 75-150
Ultra-low dose approaches
177 lbs 280 lbs
FBP Partial IR Full IRSimple Comprehensive Advanced
Ideal System
Few Iterations Advanced
model
Simple Fast
High noise
Better IQLow doseLow noise
Optimal IQLow noise
Better resolution
CPU CPU CPU
VS. VS.IRIS/ASIR/iDOSE/ADIR/SAFIRE MBIR/Veo
Blend FBP+IR
DLP 3885.82
DLP 1842.76
18 DEC 2007 22 DEC 2008
53%
Radiation Dose-ULD Stone CT
8.8
1.1
mS
v
Std dose CT ULD CTWt
CategoryCTDI mSv CTDI mSv
Over all 11.4 8.8 1.8 1.1< 200 lbs 10.6 8.6 1.3 0.8> 200 lbs 15.4 10.8 2.3 1.5
87% 90% 85%
2 view KUB
Kulkarni N M et al. Radiology 2012
=2 View KUB = 0.6 – 1.2 mSv CT KUB = < 1 mSv
Kulkarni N M et al. Radiology doi:10.1148/radiol.12112470
More aggressive dose reductionMore aggressive dose reduction
Author Year AbdomenCT
MarinD Radiology.2010
PrakashP InvestRadiol.2010
SagaraY AJRAmJRoentgenol.2010
SinghS Radiology.2010
MayMS InvestRadiol.2011
SchinderaST Radiology.2011
MartinsenAC EurJRadiol.2011
VoronaGA Pediatr Radiol.2011IQ Dos
e
20%-50%
Current Imaging Strategy
The scope of imaging has extended beyond the mere
detection of stone and its location
The current strategy is to determine the stone composition,
its fragility and quantification which has great implications in
treatment planning
Summary Points• MDCT with multiplanar reformations is accurate in stone assessment
• The qualitative assessment by CT influences management by
dictating treatment options like ESWL.
• Spectral imaging and CAD is emerging for stone
composition/Quantitation
• Various stratergies for radiation dose reduction in imaging of
urolithiasis achieving accurate diagnosis and reduced radiation dose
delivery.
• New reconstruction algorithms (ASIR) is promising in dose reduction
Dushyant V Sahani, MDDivision of abdominal imaging and intervention
Department of RadiologyMassachusetts General Hospital
White 270, 55 Fruit streetBoston, MA-02114
Email:[email protected]
Ph (o): 617-726-8396
Thank You
1. Curhan, G.C., Epidemiology of stone disease. Urol Clin North Am, 2007. 34(3): p. 287-93.2. Sandhu, C., K.M. Anson, and U. Patel, Urinary tract stones--Part I: role of radiological imaging
in diagnosis and treatment planning. Clin Radiol, 2003. 58(6): p. 415-21.3. Ege, G., et al., Acute ureterolithiasis: incidence of secondary signs on unenhanced helical CT
and influence on patient management. Clin Radiol, 2003. 58(12): p. 990-4.4. Heneghan, J.P., et al., Helical CT for nephrolithiasis and ureterolithiasis: comparison of
conventional and reduced radiation-dose techniques. Radiology, 2003. 229(2): p. 575-80.5. Boulay, I., et al., Ureteral calculi: diagnostic efficacy of helical CT and implications for treatment
of patients. AJR Am J Roentgenol, 1999. 172(6): p. 1485-90.6. Fielding, J.R., et al., Unenhanced helical CT of ureteral stones: a replacement for excretory
urography in planning treatment. AJR Am J Roentgenol, 1998. 171(4): p. 1051-3.7. Lin WC, Uppot RN, Li CS, Hahn PF, Sahani DV. Value of automated coronal reformations from
64-section multidetector row computerized tomography in the diagnosis of urinary stone disease. J Urol 2007; 178:907-911; discussion 911.
8. Smith, R.C., et al., Diagnosis of acute flank pain: value of unenhanced helical CT. AJR Am J Roentgenol, 1996. 166(1): p. 97-101.
9. Eisner BH, Iqbal A, Namasivayam S, Catalano O, Kambadakone A, Dretler SP, Sahani DV. Differences in Computed Tomography Density of the Renal Papillae of stone formers and Non-stone formers: A pilot study. J Endourol 2008 Oct 2.
10. Bilen CY, Kocak B, Kiticci G, Danaci M, Sarikaya S. Simple trigonometry on computed tomography helps in planning renal access. Urology. 2007 Aug;70(2):242-5; discussion 245
References
Jouranal/Year
DECT Technique
# Stones
• Dual Source CT: By operating the two
tubes at different energies (80 & 140 kVp)
it is effective in tissue material composition
•Gem stone spectral imaging (single
source DECT) - is a recent DE CT
operated on rapid kVp switching is also
available for tissue characterization/stone
composition
1
2
2
1
Dual-Energy CT for Stone Composition
Stolzman et al Urol Res 2008, Graser et al 2008 Invest Radiol, Graser et al 2009 Eur Radiol, Thomas et al Eur Radiol 2009
140 kV80 kV
(Syngo VA 11; Siemens)3 material decomposition algorithm
• Uric acid stones - Red
• Non Uric acid stones - Blue
Post Processing - DSDCTPost Processing - DSDCT
80
140
High and low kVp Two X-ray tube
Post Processing - SDCTPost Processing - SDCTMD IodineMD Water
Effective Z Image
Uric Acid stone = MD Water +, MD Iodine –
Non-Uric Acid stone = MD Water +, MD Iodine +High and low kVp Rapid kV twitching
Effective z number – scatter plot
Phantom Model – Uric Acid vs Non uric Acid
Accuracy Sensitivity<3mm >3mm
DSDCT(UA -16, Non UA =49)
8/8(100%)
57/57(100%)
65/65 (100%)
SDCT(UA -6, Non UA =29)
2/2(100%)
33/33(100%)
35/35 (100%)
DSDCT SDCT
MD Iodine
Uric acid Non-Uric acid Uric acid Non-Uric acid
MD Water
65 stones (Size Range- 2-18mm) 35 stones (Size range 3-19mm)
Uric acid Non-Uric acid
Dual-Energy CT for Stone Composition
Patients – Uric Acid vs Non uric AcidDSDCT SDCT
Final confirmation- 9/18 patients- 20 Stones (6 uric acid & 14 non uric acid)
37 stones Mean size-6mm, Range 2-24mm)
CT
UA 7
Non UA 23
Not Identified 7
49 stones(Mean size-6.8mm, Range 1.2-28mm)
CT
UA 15
Non UA 34
Not Identified -
Final confirmation- 3/17 patients- 8 Stones (All calcium oxalate)
Dual-Energy CT for Stone Composition
Red Blue1.15 Uric Acid Struvite, Brushite,
COM, Cystiene
1.30 Uric acidStruvite
Cystine, BrushiteCOM
1.45 Uric acidStruvite, Cystine
BrushiteCOM
1.60 Uric acid, Struvite, Brushite, COM, Cystiene
90% Cystine stones (9/10) / 84.2% Struvite stones (11/13)
SDCTPhantom Model – Differentiation of Non uric Acid
CalculatedEffective z
Effective Z
Uric Acid 6.92 7.2
Struvite 9.72 9.99
Cystine 11.07 11.25
COM 14.37 13.12
DSDCT
100% Accuracy
Dual-Energy CT for Stone Composition
Dose Reduction by 15-20%
Strategies for Dose Reduction– Coverage Area
From top of diaphragm to lower border of pubic symphysis
From Top of kidneys to base of urinary bladder
Restrict Scanning Area
Targeted scans focused to area of interest can be performed for follow up CT exams
Increase Slice thickness from 1-3mm to 5mm and include 2.5-3mm Coronal Reformations
1-3mm 5mm
Strategies for Dose Reduction - Slice Thickness
Dose Reduction by 20-40%
Strategies for Dose ReductionRole of Low kVp - Exam based on Body Weight
140 kV (> 250 lbs)
120 kV (141-249 lbs)
Dose= kVp
100/80 kV (<140 lbs)
20% reduction
20% reduction
Total 40 % Dose Reduction
Strategies for Dose Reduction- Increase in Noise Index/ reference mAs (100-180)
Noise Index -15
Noise Index -20
Noise Index -30
15-20% reduction
15-20% reduction
Total 30-40 % Dose Reduction
GE WT Slice Th mA NI
16/64-MDCT
<300 5 150-450 25- I
30 - F
>300 5 150-450 25- I
30 - F
NI- Noise indexI - Initial scanF- Follow up scan
kV (100-120)
MDCT Protocol Modifications
Siemens WT Ref mA
Sl Thick
DC Pitch
16-64 All wt group
100-160
5 24x1.2 1.2
Review Phase (116 lbs)
Monitoring Phase (114 lbs)
CTDI- 11.5
CTDI- 4.22
61%
MDCT Protocol Modifications
• MGH Experience (GE HD 750) 65 patients studied so far• Radiation dose reduction achieved (25-81%)
Adaptive Statistical Iterative Reconstruction (ASIR)
• Noise reduction reconstruction method to improve the
signal-to-noise
• Relies on the accurate modeling of the distribution of
noise in the acquired data
Kole et al 2006 Phys Med Biol