CT-Urography

CT Urography Stuart G. Silverman, M.D. Professor of Radiology Harvard Medical School Director, Abdominal Imaging and Intervention Brigham and Women’s Hospital Boston, MA Ureter CT Urography Stuart G. Silverman, M.D. Disclosure of financial relationship with relevant commercial interest Siemens Medical Solutions Malverne , PA – Consultant Ureter Outline • CT urography technique • Ureter variants • Ureter: benign vs malignant • Dual energy applied to ureter • Summary BWH CTU Protocols Patients > 40 years old • Three phase – UP (abdomen and pelvis), NP (kidneys only), EP (abdomen and pelvis), supplemented with 10 mg furosemide IV Patients < 40 years old • Split bolus, two phase – abdomen and pelvis, supplemented with 250 cc saline IV BWH CT Urography Protocol 64 – Channel MDCT with 3 phases 10 mg IV Furosemide 2-3” CM (100cc) Unenhanced Range Abd/Pel Delay -Collimation 1.2 mm Axial Recon/Incr 3/3 Post Processing -- Nephrographic Excretory Kidneys Abd/Pel 100 s 10 - 15 min 1.2 mm 0.6 mm 3/1.5 3/3 -- Cor / Sag / MIP / CPR / VR Iodinated contrast material (300 mgI/ml); 0.5 s rotation time AEC w/ quality reference 200 mAs, 120 kVp Silverman et al Radiology 2006 BWH CT Urography Protocol 64 – Channel MDCT with 3 phases 10 mg IV Furosemide 2-3” CM (80cc) Unenhanced Range Abd/Pel Delay -Collimation 1.2 mm Axial Recon/Incr 3/3 Post Processing -- Nephrographic Excretory Kidneys Abd/Pel 100 s 10 - 15 min 1.2 mm 0.6 mm 3/1.5 3/3 -- Cor / Sag / MIP / CPR / VR Iodinated contrast material (370 mgI/ml); 0.5 s rotation time AEC w/ quality reference 200 mAs, 120 kVp Silverman et al Radiology 2006 IV Furosemide Withheld • Furosemide allergy • Sulfa allergy • SBP < 90 torr IV Saline is suitable alternative BWH CT Urography Protocol 64 – Channel MDCT with 3 phases CM (80cc) Unenhanced Range Abd/Pel Delay -Collimation 1.2 mm Axial Recon/Incr 3/3 Post Processing -- IV Saline(250 ccs) Nephrographic Excretory Kidneys Abd/Pel 100 s 10 - 15 min 1.2 mm 0.6 mm 3/1.5 3/3 -- Cor / Sag / MIP / CPR / VR Iodinated contrast material (370 mgI/ml); 0.5 s rotation time AEC w/ quality reference 200 mAs, 120 kVp McTavish et al Radiology 2002 BWH CTU Protocol for pts < 40 y.o. Split dose 370 mgI/ml CM (40cc) Unenhanced Range Abd/Pel Delay -Collimation 2.5 mm Axial Recon/Incr 3/3 Post Processing -- (80 cc) NP + EP Abd/Pel 6 min 100 sec 2.5 mm Saline 3/3 Cor / Sag / MIP / CPR / VR Modified from Chow and Sommer AJR 2001 Chai et al Australas Radiol 2001 Obtaining NP and EP during one scan reduces radiation dose Indications: Full CT Urogram • Hematuria • Suspected urothelial cancer (e.g., positive urine cytology) • Follow-up urothelial cancer • Hydronephrosis ?etiology • Others? Urinary Tract CT Protocols • Flank pain - > UP (“Stone protocol”) • Renal mass - > UP, NP, Excretory (Kidney) • Congenital anomalies - > Excretory • Partial nephrectomy - > AP, VP, Excretory • Post-operative Comp - > Excretory • Trauma -> NP, Excretory UP = unenhanced phase; NP = nephrographic phase AP = arterial phase; VP = venous phase Ureteral Mass-like findings • Lumenal – stone, clot, mycetoma, sloughed papilla, mucus • Mucosal – tumor, stricture • Mural – ureteritis cystica, met, leiomyoma • Extramural – RPF, LN, mass More Ureteral Ca Look-Alikes • Endometriosis • Leukoplakia • Cholesteatoma • Malacoplakia • Tuberculosis Is CTU Good in detecting UT TCC? • • • UT TCC is uncommon UT TCC occur in up to 6.5% of pts w/ known or prior bladder ca. Upper tract needs to be evaluated at the time bladder cancer is diagnosed and periodically in surveillance. Yousem DM. et al. Synchronous and metachronous transitional cell carcinoma of the urinary tract. Radiology 1988;167:613-618. Is CTU Good in Detecting UT TCC? 82 (3%) positive CT urograms (n=2602) 50 40 43 39 30 20 10 0 True Positive False Positive PPV: 43/82 = 52% Sadow et al AJR (in press) Is CTU Good in Detecting UT TCC? CTU + True + 40PPV = 81% 36 30 29 PPV = 0% 20 17 10 0 PPV = 48% 29 14 0 Large Mass (>5 mm) Small Mass (</=5 mm) Urothelial Thickening Sadow et al AJR (in press) Is CTU Good in Detecting UT TCC? • • • • The PPV (52%) of CTU for detection of upper tract malignancies is moderate, as benign findings mimic cancer Large (> 5 mm) masses are likely to be cancers Small (< 5 mm) masses are unlikely to be cancers Urothelial thickening is just as likely to be benign as malignant Sadow et al AJR (in press) Imaging Algorithm for Hematuria MDCTU Renal cyst Renal mass Normal Urothelial abn Thickening MRI Retro Pyelogram Note.- Retrograde pyelography may still be needed when CTU is positive… Single Energy CT One x-ray tube, one acquisition… compact bone CT-value (HU) 1000 80 800 600 spong. bone 40 water fat -200 -600 -800 -1000 pancreas 50 200 -400 blood 60 400 0 liver 70 kidney 30 20 lungs 10 0 Materials differentiated based on attenuations Courtesy Christianne Leidecker SMS Dual Energy CT Dual source method… Tube B • Two x-ray tubes – kVp same or different • Tube B = 80 kVp, FOV 26 cm (33 cm) Tube A 26 cm • Tube A = 140 kVp, FOV= 50 cm 50 cm 17 Number of photons x 1017 Dual Energy CT ! c i at m o r h yc l 5 o p re a s m 4 bea y a r X56 keV 76 keV Mean Energy! 3 140 kVp, mean 76 keV 80 Kvp, mean 56 keV Mean Energy! 2 Tube A Tube B 140 kVp 1 80 kVp 0 50 100 Photon Energy ((keV) keV) Peak Energy! 150 Dual Energy CT Basic concepts… • X-ray attenuation is determined by two independent absorption process, compton scatter and photoelectric effect Photoelectic effects greater at lower kVp, and soar at k edge Compton effect is constant Dual Energy CT Basic concepts… • Total attenuation decreases with increasing energy • Attenuation depends on energy (keV) and material density • X-ray absorption depends on the inner electron shells. • DECT is sensitive to atomic number and density Dual Energy CT Attenuation (cm22/g) 1000 100 Iodine Calcium Water Fat 56 keV 76 keV 10 Large increase 1 Small increase 0.1 0 50 100 150 Photon Energy ((keV) keV) 200 Dual Energy CT Basic concepts… • DECT can be used to determine concentration of three known materials • DECT cannot be used to determine the chemical composition of an unknown material Dual Energy CT - Stones HU @ 80 kV +200 Iodine +65 Soft Tissue 0 --100 100 Fat --90 90 0 +60 +100 HU @ 140 kV Stone Composition – Why? • • • Uric acid stones managed with urine alkalinization; prevented with allopurinol Calcium stones managed with SWL, PCNL, or ureteroscopy; prevented with thiazides Calcium monohydrate (high HU and homogeneous), brushite, and cystine (particularly >15 mm) stones are resistant to ESWL Kim et al Urol Res 2007 Perks et al Urology 2008 CT Attenuations – Why not? • Overlapping attenuation ranges • Stones are typically mixed • HU measurements are variable and dependent on CT technique (including dose, collimation, section thickness) Kambadakone et al RadioGraphics 2010 Dual Energy CT - Stones • • • • Attenuation depends on density, atomic number, and the energy of the X-ray beam. The higher the atomic number, the higher the attenuation Calcium oxalate (CaC2O4), calcium phosphate (Ca3(PO4)2), and cystine (C6H12N2O4S2) contain elements with high atomic numbers (Ca = 20, S = 16, P = 15) or ‘heavy’ chemical elements. Uric acid (C5H4N4O3) and struvite (MgNH4PO46H2O) are composed of elements with low atomic numbers, or ‘light’ chemical elements Thomas et al Eur Rad 2009 (H,C,N,O) Primak et al Acad Rad 2007 Dual Energy CT - Stones • • • • As a consequence, uric acid (UA) stones have higher attenuations at higher kVp than at lower kVp, whereas non-UA stones have a higher attenuation at lower kVp than at higher kVp Most non-UA stones contain calcium A three-material decomposition first assumes that all voxels contain a mixture of water (urine), calcium, and UA. If the voxel exhibits DE behavior similar to calcium, it is assigned a blue color, UA red, and voxels that show a linear density at both tube potentials remain gray (Graser Invest Rad 2007) Thomas et al Eur Rad 2009 Primak et al Acad Rad 2007 Dual Energy CT - Stones • • • Commercially available software uses a threematerial decomposition algorithm (Syngo DE Viewer, SMS). Stone is considered a mixture of a hypothetical “pure” stone with no pores (such a stone would have high attenuation) and the material that fills the pores, urine. On a plot of attenuations @ 80 kVp vs 140 kVp, a real stone has to lie somewhere, depending on its porosity, between urine and a pure stone. Primak et al Acad Rad 2007 Dual Energy CT - Stones HU @ 80 kV Calcium stones have more attenuation at lower kVp, hence DE ratio (HU @80 kVp / HU @ 140 kVp) will be higher Hence the slope can be correlated w/ stone composition Calcium stones along this line “Pure” stone All stones of a particular type will be represented along this line, depending on the porosity… “Urine” HU @ 140 kV Primak et al Acad Rad 2007 Dual Energy CT - Stones Sin dif gle a fer en vera g tc alc e sl ium ope -co rep nta res e i ni n g nts s to ne s HU @ 80 kV “Pure” calcium stone Stones below angle bisector are characterized as UA stones, above as non-UA or calcium stones “Pure” uric acid stone “Urine” HU @ 140 kV Primak et al Acad Rad 2007 Dual Energy CT - Stones Dual Energy CT Urography 140 kVp 80 kVp 30/70 Summary • MDCT urography supplemented with IV furosemide can be used to evaluate the ureter • Thin (3 mm) sections and multiplanar reformations, particular CPR, are helpful when evaluating the ureter • Beware of benign entities that mimic cancer. • DECT can be used to differentiate urate stones from non-urate stones.