Kidney Stone Diagnosis and Managment

HARVARD
MEDICAL SCHOOL
Kidney Stone Diagnosis and
Managment
Dushyant Sahani MD
Disclosures
• MGH has research agreement
– GE Health Care
– Siemens Medical Systems
Clinical Perspective
5.2%
Prevalence
of
Urolithiasis
Rising Prevalence
3.2%
1970s
1980s
1990s
•
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
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
Composition
Radioopacity
Occurrence
Calcium oxalate monohydrate
(COM) & dehydrate (COD)
Hydroxyapatite
(Calcium phosphate)
On KUB
On CT
40-60% Radio-opaque Radio-opaque
20-60%
Radio-opaque Radio-opaque
Brushite
2- 4%
Radio-opaque Radio-opaque
Uric Acid
5-10%
Radio- lucent Radio-opaque
Struvite
5-15%
Radio-opaque Radio-opaque
Cystine
1- 2.5%
Mildly Opaque Radio-opaque
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
Slice thickness – 3-5 mm
Pitch - 1 - 1.6
Coronal Reformations
(2.5 - 3mm)
Urolithiasis –CT Diagnostic Signs
Virtually all stones are
Primary sign of Ureterolithiasis
radio-opaque on CT (>200HU)
Stone in the ureter (target sign) with proximal
hydroureter
Stones radiolucent on CT - Pure matrix stones and stones made of pure Indinavir
(Indinavir - Protease inhibitor used in the treatment of HIV)
Value of Coronal Reformations
1
2
•
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
Lin WC et al. J Urol 2007.
Factors Influencing Treatment Decision
Urologic intervention is influenced by 3 crucial factors
Stone size/
location
Stone
Patient
Symptoms Composition
Presence of obstruction is not the primary factor
considered for urologic intervention
•
•
•
Bierkens AF et al. Br J Urol. 1998.
Eisner BH et al. Urology 2008.
Phipps S et al. Ann R Coll Surg Eng 2010.
Stone Burden Assessment
• 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 Size
• 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
8mm
Soft tissue window
6 mm
Bone window with
Magnification
Eisner BH et al. J Urol 2009
Stone Size & Treatment Decisions
Stone < 5mm
(98% for stones < or = 4mm
pass spontaneously)
Stones > 6mm & <15mm
Stone >15mm or Staghorn Calculi
(6-9 mm uereteral stone 60-25% pass)
Stone location predicts outcome
Upper=48%, mid=60%, lower 75-79%
likely to 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)
Percutaneous
Nephrolithotomy
(PCNL)
•
•
•
•
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.
Stone Volumetry
22 cc
Threshold based
CAD Algorithms
or manual semiautomated
methods
• 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
•
•
Demehri S et al. AJR 2012.
Singh Ak et al. RSNA 2010.
ESWL Failure: Multivariate CT
characteristics
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 VolumeProducts
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
Singh Ak et al. RSNA 2010.
Stone Composition & Treatment Decisions
> 500 HU
<400 HU
Uric Acid Stone
Medical Management
Allopurinol
Treatment of Hyperuricemia
<1000 HU
(Struvite)
>1000HU
(Brushite, Cystine, COM)
ESWL
Ureteroscopy
PCNL
Hamm M et al. J Urol 2002.
Parker BD et al. Urology 2004
MDCT and Stone Composition
Stone 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 2001
Motley G et al. Urol 2001
Eisner BH et al. J Urol 2009
KulkarniN et al. JCAT (in-press)
DECT: Stone composition
Element composition
Attenuation at 80
Uric Acid Stone
Non uric acid stone
Light Elements
(H, C, N, O)
Heavy Elements
(P, Ca, S)
Lower HU
Higher HU
Higher HU
Lower HU
kVp
Attenuation at 140
kVp
Calcium
710 HU
Uric Acid
290 HU
80kV
Calcium
480 HU
Uric Acid
315 HU
140kV
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
Heterogenous
More fragile to
Lithotripsy
Homogenous
More resistant
to lithotripsy
•
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
Stone Precursor-Randall’s Plaque
• Randall’s Plaque - Calcium salt deposits
30 HU
in the tip of renal papilla of patients with
Normal papillae
nephrolithiasis and are potential sites for
calculus formation
• These stone bearing papillae appear
Whitish deposits
- Randall’s plaque
denser on non-contrast CT and represent
Randall’s plaque on endoscopy
• MDCT can help select patients at highrisk for stone formation, who may
undergo appropriate medical
management to halt the formation of
58 HU
stones
Stone bearing papillae
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
Stone Follow up
In patients managed medically,
CT attenuation is a good predictor of utility of radiography in routine follow up
>300 HU
Follow up Radiograph
Calculi with attenuation > 300 HU are
radio-opaque & are followed up by
Abdominal Radiograph
<200 HU
Follow up CT
Calculi with attenuation < 200 HU are
radiolucent & hence followed up by CT
Stone Follow up –Post Intervention
Pre Treatment
Significant Stone Burden
Post Treatment
Residual Stone Burden
though significantly reduced
Significant stone burden necessitates further treatment
Stone vs Stent
Abdominal window
Bone window
Stent
Stones
•
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.
Tanricut C et al. Urology 2004
MDCT and Radiation Dose
•
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)
Strategies for Dose Reduction
Limit
Scanning area
Increase slice thickness
Include coronal reformations
+
DLP
1000 mGy-cm
Total Dose Reduction
by 40-70% from
Standard dose
Low kVp
+
Low mAs
+
DLP
200 mGy-cm
Ultra-low dose approaches
Renal stone
Initial scan – Standard dose CT (low mAs)
Follow up scan – ultra-low dose CT
Low dose CT
WT
kVp
mA
<200 lbs
80
75-150
> 200 lbs
100
75-150
Ultra-low dose approaches
177 lbs
280 lbs
IRIS/ASIR/iDOSE/ADIR/SAFIRE
FBP
Simple
VS.
Partial IR
Comprehensive
MBIR/Veo
VS.
Full IR
Advanced
Blend
FBP+IR
Few
Iterations
Ideal
System
CPU
Simple
Fast
High noise
CPU
Better IQ
Low dose
Low noise
Advanced
model
CPU
Optimal IQ
Low noise
Better resolution
18 DEC 2007
22 DEC 2008
DLP 388
5.82
DLP 184
2.76
53%
Radiation Dose-ULD Stone CT
mSv
8.8
87%
90%
85%
1.1
2 view KUB
Wt
Category
Over all
< 200 lbs
> 200 lbs
Std dose CT
CTDI
mSv
11.4
10.6
15.4
Kulkarni N M et al. Radiology 2012
8.8
8.6
10.8
ULD CT
CTDI
mSv
1.8
1.3
2.3
1.1
0.8
1.5
More aggressive dose reduction
=
2 View KUB = 0.6 – 1.2 mSv
CT KUB = < 1 mSv
Kulkarni N M et al. Radiology doi:10.1148/radiol.12112470
Author
Year
MarinD
Radiology.2010
PrakashP
InvestRadiol.2010
SagaraY
AJRAmJRoentgenol.2010
SinghS
Radiology.2010
MayMS
InvestRadiol.2011
SchinderaST
Radiology.2011
MartinsenAC
EurJRadiol.2011
VoronaGA
Pediatr Radiol.2011
AbdomenCT
20%50%
IQ
Dos
e
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
Thank You
Dushyant V Sahani, MD
Division of abdominal imaging and intervention
Department of Radiology
Massachusetts General Hospital
White 270, 55 Fruit street
Boston, MA-02114
Email:dsahani@partners.org
Ph (o): 617-726-8396
References
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 Nonstone 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
Jouranal/Yea
r
DECT
Technique
# Stones
Dual-Energy CT for Stone
Composition
• Dual Source CT: By operating the two
1
2
2
1
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
Stolzman et al Urol Res 2008, Graser et al 2008 Invest Radiol, Graser et al 2009 Eur
Radiol, Thomas et al Eur Radiol 2009
Post Processing - DSDCT
80 kV
140 kV
80
140
High and low kVp
Two X-ray tube
• Uric acid stones - Red
• Non Uric acid stones - Blue
(Syngo VA 11; Siemens)
3 material decomposition algorithm
Post Processing - SDCT
MD Water
Uric Acid stone =
High and low kVp
Rapid kV twitching
MD Iodine
MD Water +, MD Iodine –
Non-Uric Acid stone = MD Water +, MD Iodine +
Effective Z Image
Effective z number – scatter plot
Dual-Energy CT for Stone
Composition
Phantom Model – Uric Acid vs Non uric Acid
SDCT
DSDCT
65 stones (Size Range- 2-18mm)
35 stones (Size range 3-19mm)
MD Water
Uric acid
Uric acid
Non-Uric acid
Accuracy
DSDCT
(UA -16, Non UA =49)
SDCT
(UA -6, Non UA =29)
MD Iodine
Non-Uric acid
Uric acid
Sensitivity
<3mm
>3mm
8/8
(100%)
57/57
(100%)
65/65
(100%)
2/2
(100%)
33/33
(100%)
35/35
(100%)
Non-Uric acid
Dual-Energy CT for Stone
Composition
Patients – Uric Acid vs Non uric Acid
DSDCT
SDCT
37 stones
Mean size-6mm, Range 2-24mm)
49 stones
(Mean size-6.8mm, Range 1.2-28mm)
CT
CT
UA
7
UA
15
Non UA
23
Non UA
34
Not Identified 7
Final confirmation
- 9/18 patients
- 20 Stones (6 uric acid & 14 non uric acid)
Not Identified Final confirmation
- 3/17 patients
- 8 Stones (All calcium oxalate)
Dual-Energy CT for Stone
Composition
Phantom Model – Differentiation of Non uric Acid
DSDCT
1.15
Red
Blue
Uric Acid
Struvite, Brushite,
COM, Cystiene
SDCT
Calculated
Effective z
Effective Z
Uric Acid
6.92
7.2
1.30
Uric acid
Struvite
Cystine, Brushite
COM
Struvite
9.72
9.99
1.45
Uric acid
Struvite, Cystine
Brushite
COM
Cystine
11.07
11.25
1.60
Uric acid, Struvite,
Brushite, COM,
Cystiene
COM
14.37
13.12
90% Cystine stones (9/10) /
84.2% Struvite stones (11/13)
100% Accuracy
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
Dose Reduction by 15-20%
Targeted scans focused to area of interest can be performed for follow up CT exams
Strategies for Dose Reduction - Slice Thickness
1-3mm
5mm
Increase Slice thickness from 1-3mm to 5mm
and include 2.5-3mm Coronal Reformations
Dose Reduction by 20-40%
Strategies for Dose Reduction
Role of Low kVp - Exam based on Body Weight
140 kV (> 250 lbs)
Dose=
kVp
120 kV (141-249 lbs)
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
MDCT Protocol Modifications
GE
16/64MDCT
WT
Slice Th
mA
NI
<300
5
150-450
25- I
30 - F
>300
5
150-450
25- I
30 - F
NI- Noise index
I - Initial scan
F- Follow up scan
Siemens
WT
Ref
mA
Sl
Thick
DC
Pitch
16-64
All wt
group
100160
5
24x1.2
1.2
kV (100-120)
MDCT Protocol Modifications
Review Phase (116 lbs)
Monitoring Phase (114 lbs)
61%
CTDI- 11.5
CTDI- 4.22
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
•
MGH Experience (GE HD 750) 65 patients studied so far
• Radiation dose reduction achieved (25-81%)
Kole et al 2006 Phys Med Biol