PRINCIPLES OF CT SCAN PRINCIPLES OF CT SCAN ABDOMEN ABDOMEN

GUIDE- PROF.DR P. K. PANDEY(M.S)GUIDE- PROF.DR P. K. PANDEY(M.S) PROFESSOR,DEPT. OF SURGERYPROFESSOR,DEPT. OF SURGERY

PRESENTED BY-PRESENTED BY- PRAKASH CHINNANNAVARPRAKASH CHINNANNAVAR

HISTORY OF CT SCANHISTORY OF CT SCAN

1917-J RADON,WORKING WITH 1917-J RADON,WORKING WITH GRAVITATIONAL THEORYGRAVITATIONAL THEORY

1956-BRACEWELL WORKING IN 1956-BRACEWELL WORKING IN RADIOASTRONOMYRADIOASTRONOMY

1961-OLDENDORF UNDERSTOOD 1961-OLDENDORF UNDERSTOOD CONCEPT OF CTCONCEPT OF CT

1972-G.N.HOUNSFIELD PUT A CT SYSTEM 1972-G.N.HOUNSFIELD PUT A CT SYSTEM TOGETHER.TOGETHER.

HISTORY OF CT SCANHISTORY OF CT SCAN

CT was originally proposed and used as an extension of the CT was originally proposed and used as an extension of the basic X-ray: doctors wanted to see inside the head, but basic X-ray: doctors wanted to see inside the head, but standard X-ray techniques could not penetrate the dense skull standard X-ray techniques could not penetrate the dense skull while distinguishing soft tissueswhile distinguishing soft tissues

The first scanners could only do one slice at a time and each The first scanners could only do one slice at a time and each slice took 4 minutes to complete slice took 4 minutes to complete

By 1976, whole body scanners were developedBy 1976, whole body scanners were developed Today’s machines can acquire a slice in less than half a Today’s machines can acquire a slice in less than half a

second (.1 second for the GE top-end multislice LightSpeed second (.1 second for the GE top-end multislice LightSpeed Pro16 with Xtream)Pro16 with Xtream)

Advancements still occurring through new technologyAdvancements still occurring through new technology

COMPUTED TOMOGRPHYCOMPUTED TOMOGRPHY BASIC PRINCIPLEBASIC PRINCIPLE of CT is that the internal of CT is that the internal

structure of an object can be reconstructed from structure of an object can be reconstructed from multiple projections of that object.multiple projections of that object.

The ray projections are formed by scanning a The ray projections are formed by scanning a thin cross section of the body with a narrow x-thin cross section of the body with a narrow x-ray beam and measuring the transmitted ray beam and measuring the transmitted radiation with a sensitive radiation detector. radiation with a sensitive radiation detector.

The detector adds up the energy of all the The detector adds up the energy of all the transmitted photon. The numerical data from transmitted photon. The numerical data from multiple ray sums are than computer processed multiple ray sums are than computer processed to reconstruct an image. to reconstruct an image.

CT SCANNERCT SCANNER

It is having 3 component–It is having 3 component–1. X-ray tube1. X-ray tube2. collimator2. collimator3. Detector –two types of 3. Detector –two types of

detectors used in CT detectors used in CT scanner-scanner-

Scintillation crystalsScintillation crystals Xenon gas ionisation Xenon gas ionisation

chamberschambers

• various designs of CT scanner-various designs of CT scanner-

1. First generation (translate –rotate ,one detector )1. First generation (translate –rotate ,one detector )

2. Second gen. (translate – rotate ,two detector)

Third gen. (rotate – rotate ) Fourth gen. (rotate –fixed)Third gen. (rotate – rotate ) Fourth gen. (rotate –fixed)

- - In CT cross section of body is divided into many tiny In CT cross section of body is divided into many tiny blocks and each is assigned a number proportional blocks and each is assigned a number proportional to the degree that the block attenuate the x-ray to the degree that the block attenuate the x-ray beam.beam.

- The linear attenuation coefficient (µ) is used to - The linear attenuation coefficient (µ) is used to quantitate attenuation and is determined by quantitate attenuation and is determined by composition and thickness of ‘voxel’ ,along with composition and thickness of ‘voxel’ ,along with quality of the beam .quality of the beam .

- CT numbers are derived by comparing linear - CT numbers are derived by comparing linear attenuation coefficient of a pixel with that of water attenuation coefficient of a pixel with that of water and are described in HOUNSFIELD UNIT . and are described in HOUNSFIELD UNIT .

IMAGE RECONSTRUCTIONIMAGE RECONSTRUCTION

•

CT density scale :-CT density scale :-

Water – ‘0’ HUWater – ‘0’ HU

Air - ‘-1000’ HUAir - ‘-1000’ HU

Calcification – ‘+1000’ HUCalcification – ‘+1000’ HU

Fat - ‘-100’ HUFat - ‘-100’ HU

Hemorrhage – ’60-70’ HU Hemorrhage – ’60-70’ HU Bone appears white; gases and liquids are

black; tissues are gray

Improvements over X-RaysImprovements over X-Rays

Provides 3D images Provides 3D images and cross-sectional and cross-sectional views instead of basic views instead of basic 2D images2D images

CT Scans can show CT Scans can show soft tissue as well as soft tissue as well as bone, allowing bone, allowing physicians to detect problems such as cancerous tumorsphysicians to detect problems such as cancerous tumors

Extremely helpful in determining organ anatomy, especially Extremely helpful in determining organ anatomy, especially following traumafollowing trauma

Can determine tissue density difference of less than 1% while X-Can determine tissue density difference of less than 1% while X-rays can allow determine tissue density difference of 5%rays can allow determine tissue density difference of 5%

                                                                              Circa 1975, in the Circa 1975, in the early days of the CT early days of the CT scan.scan.

                                                                              A present-day A present-day scan, showing a scan, showing a six-fold increase six-fold increase in detail in detail

History of CT Scan (continued)History of CT Scan (continued)

SpecificationsSpecifications First CT (circa First CT (circa 1970)1970)

Modern CT Modern CT Scanner Scanner (2001)(2001)

Time to acquire one Time to acquire one CT image CT image

4-5 minutes4-5 minutes 0.5 seconds0.5 seconds

Pixel size Pixel size 3 mm x 3 mm3 mm x 3 mm 0.5 mm x 0.5 mm0.5 mm x 0.5 mm

Number of pixels in an Number of pixels in an image image

64,00064,000 256,000256,000

Aliasing Artifact or StreaksAliasing Artifact or Streaks

These appear as dark lines which radiate away These appear as dark lines which radiate away from sharp corners. It occurs because it is impossible for from sharp corners. It occurs because it is impossible for the scanner to 'sample' or take enough projections of the the scanner to 'sample' or take enough projections of the object, which is usually metallic. It can also occur when object, which is usually metallic. It can also occur when an insufficient X-ray tube current is selected, and an insufficient X-ray tube current is selected, and insufficient penetration of the x-ray occurs. These insufficient penetration of the x-ray occurs. These artifacts are also closely tied to motion during a scan. .artifacts are also closely tied to motion during a scan. .

ArtifactsArtifacts

Ring Artifact

Probably the most common mechanical artifact, the image of one or many 'rings' appears within an image. This is usually due to a detector fault

Noise ArtifactNoise Artifact This appears as graining on the image and is caused by This appears as graining on the image and is caused by

a low signal to noise ratio. This occurs more commonly a low signal to noise ratio. This occurs more commonly when a thin slice thickness is used. It can also occur when a thin slice thickness is used. It can also occur when the power supplied to the X-ray tube is insufficient when the power supplied to the X-ray tube is insufficient to penetrate the anatomyto penetrate the anatomy..

Motion ArtifactMotion Artifact This is seen as blurring and/or streaking which is caused This is seen as blurring and/or streaking which is caused

by movement of the object being imaged.by movement of the object being imaged.

Beam HardeningBeam Hardening This can give a 'cupped appearance'. It occurs when This can give a 'cupped appearance'. It occurs when

there is more there is more attenuation in the center of the object than in the center of the object than around the edge. This is easily corrected by filtration and around the edge. This is easily corrected by filtration and software.software.

HELICAL/SPIRAL SCANNINGHELICAL/SPIRAL SCANNING

CONTRAST MATERIALCONTRAST MATERIAL

1. Ionic monomeric contrast media (high-osmolar1. Ionic monomeric contrast media (high-osmolar contrast media, HOCM), contrast media, HOCM), e.g. amidotrizoate,e.g. amidotrizoate, iothalamate, ioxithalamateiothalamate, ioxithalamate

2. Ionic dimeric contrast media (low-osmolar contrast2. Ionic dimeric contrast media (low-osmolar contrast media, LOCM), e.g. media, LOCM), e.g. ioxaglateioxaglate

3. Nonionic monomeric contrast media (low-osmolar3. Nonionic monomeric contrast media (low-osmolar contrast media, contrast media, LOCM), e.g. iohexol, iopentol,LOCM), e.g. iohexol, iopentol, ioxitol, iomeprol, ioversol, iopromide, ioxitol, iomeprol, ioversol, iopromide, iobitridol,iobitridol,

iopamidoliopamidol 4. Nonionic dimeric contrast media (iso-osmolar4. Nonionic dimeric contrast media (iso-osmolar contrast media, IOCM), contrast media, IOCM),

e.g. iotrolan, iodixanol e.g. iotrolan, iodixanol

Risks of CT ScanRisks of CT Scan Low-risk procedureLow-risk procedure Main risk is allergic reaction to contrast Main risk is allergic reaction to contrast

dye, often mild and resulting in itching, dye, often mild and resulting in itching, hives, or a rashhives, or a rash

More radiation than modern standard X-More radiation than modern standard X-Ray, but still minimal amountRay, but still minimal amount

Only radiation risk significant only for Only radiation risk significant only for pregnant women pregnant women

Which CT Scanner is best?Which CT Scanner is best?

Axial v. Helical scannersAxial v. Helical scannersAxial scannersAxial scanners

Longer time to scanLonger time to scan Danger in misregistration of scannerDanger in misregistration of scanner

Helical scannersHelical scanners Quicker scan timeQuicker scan time Images for overlapping slices can be generatedImages for overlapping slices can be generated More complicated image reconstructionMore complicated image reconstruction

Single-slice vs. Multi-slice detectorsSingle-slice vs. Multi-slice detectors

Single-slice detectorsSingle-slice detectorsSlow exam timesSlow exam times

Multi-slice detectorsMulti-slice detectorsMuch quicker exam timesMuch quicker exam timesUp to 4 slices in 0.5 secondsUp to 4 slices in 0.5 seconds

What typically gets scannedWhat typically gets scanned

brain and spinal abnormalitiesbrain and spinal abnormalities brain tumors and strokesbrain tumors and strokes sinusitis sinusitis aortic aneurysms and other blood vesselsaortic aneurysms and other blood vessels hemorrhagehemorrhage chest infectionschest infections diseases of organs such as the liver, kidneys, diseases of organs such as the liver, kidneys,

and lymph nodes in the abdomen. and lymph nodes in the abdomen.

CONTRAINDICATIONS CONTRAINDICATIONS FOR CT SCANFOR CT SCAN -CONTRAST ALLERGY-CONTRAST ALLERGY

-CLAUSTROPHOBIA-CLAUSTROPHOBIA

-PREGNANCY-PREGNANCY

CT APPLICATIONSCT APPLICATIONS

LIVERLIVER

LIVERLIVER

HEPATIC PARENCHYMAHEPATIC PARENCHYMA

ATTENUATION VALUE AROUND 45-65ATTENUATION VALUE AROUND 45-65

HEPATICSPLENIC ATTENUATION DIFFERENCEHEPATICSPLENIC ATTENUATION DIFFERENCE

AFTER IV CONTRAST ADMINISTRATION THIS ATTENUATION DIFFERENCE AFTER IV CONTRAST ADMINISTRATION THIS ATTENUATION DIFFERENCE REVERSESREVERSES

PRINCIPLES OF HEPATIC PRINCIPLES OF HEPATIC CONTRAST ENHANCEMENTCONTRAST ENHANCEMENT TO INCREASE ATTENUATION VALUE DIFFERENCE BETWEEN TO INCREASE ATTENUATION VALUE DIFFERENCE BETWEEN

LIVER LESIONS AND NORMAL HEPATIC PARENCHYMALIVER LESIONS AND NORMAL HEPATIC PARENCHYMA

ATTENUATION VALUE DEPENDS ON ATTENUATION VALUE DEPENDS ON HISTOLOGY,VASCULARITY,NECROSIS,CALCIFICATION,HEMOHISTOLOGY,VASCULARITY,NECROSIS,CALCIFICATION,HEMORRAGE.RRAGE.

USUALLY HEPATIC NEOPLASMS HAVE LOWER ATTENUATION USUALLY HEPATIC NEOPLASMS HAVE LOWER ATTENUATION VALUE THAN NORMAL LIVER EXCEPT IN DIFFUSE FATTY VALUE THAN NORMAL LIVER EXCEPT IN DIFFUSE FATTY LIVER WHERE THEY ARE HYERATTENUATINGLIVER WHERE THEY ARE HYERATTENUATING

HEPATIC CONTRAST HEPATIC CONTRAST ENHANCEMENTENHANCEMENT VASCULARVASCULAR REDISTRIBUTION REDISTRIBUTION EQUILIBRIUMEQUILIBRIUM

HEPATIC CYSTHEPATIC CYST

BILIARY HAMARTOMASBILIARY HAMARTOMAS

LIVER HEMANGIOMASLIVER HEMANGIOMAS

FOCAL NODULAR HYPERPLASIAFOCAL NODULAR HYPERPLASIA

HEPATOCELLULAR ADENOMAHEPATOCELLULAR ADENOMA

HEPATOCELLULAR CARCINOMAHEPATOCELLULAR CARCINOMA

FIBROLEMELLAR FIBROLEMELLAR HEPATOCELLULAR CARCINOMAHEPATOCELLULAR CARCINOMA

METASTASIS TO LIVERMETASTASIS TO LIVER

PYOGENIC LIVER ABSCESSPYOGENIC LIVER ABSCESS

HYDATID CYST OF LIVERHYDATID CYST OF LIVER

BILARY SYSTEMBILARY SYSTEM

PRINCIPLES OF BILIARY TRACT PRINCIPLES OF BILIARY TRACT IMAGINGIMAGING USG IS INITIAL IMAGING STUDYUSG IS INITIAL IMAGING STUDY CT DETECTS BILIARY CT DETECTS BILIARY

DILATATION,BILIARY WALL DILATATION,BILIARY WALL THICKENING,DUCTAL THICKENING,DUCTAL STONES,PANCREATIC MASS, STONES,PANCREATIC MASS, ADENOPATHYADENOPATHY

PORCELAIN GALL BLADDERPORCELAIN GALL BLADDER

GALL BLADDER CARCINOMAGALL BLADDER CARCINOMA

CAROLI’S DISEASECAROLI’S DISEASE

CHOLEDOCOLITHIASISCHOLEDOCOLITHIASIS

MIRIZZI SYNDROMEMIRIZZI SYNDROME

INTAHEPATIC INTAHEPATIC CHOLANGIOCARCINOMACHOLANGIOCARCINOMA

SPLEENSPLEEN

SPLENIC CYSTSSPLENIC CYSTS

NON HODGKIN’S LYMPHOMANON HODGKIN’S LYMPHOMA

HODGKIN’S LYMPHOMAHODGKIN’S LYMPHOMA

PANCREASPANCREAS

PANCREATIC CARCINOMAPANCREATIC CARCINOMA

CHRONIC PANCREATITISCHRONIC PANCREATITIS

MUCINOUS CYSTIC NEOPLASMMUCINOUS CYSTIC NEOPLASM

GASTRINOMAGASTRINOMA

ACUTE PANCREATITISACUTE PANCREATITIS

CHRONIC PANCREATITISCHRONIC PANCREATITIS

PSEUDOPANCREATIC CYSTPSEUDOPANCREATIC CYST

INFECTED PANCREATIC INFECTED PANCREATIC NECROSISNECROSIS

RETROPERITONEUMRETROPERITONEUM

RETROPERITONEAL RETROPERITONEAL HEMATOMAHEMATOMA

IDEOPATHIC IDEOPATHIC RETROPERITONEAL FIBROSISRETROPERITONEAL FIBROSIS

RETROPERITONEAL SARCOMARETROPERITONEAL SARCOMA

PSOAS ABSCESS FROM PSOAS ABSCESS FROM INFECTED URINOMAINFECTED URINOMA

HORSESHOE KIDNEYHORSESHOE KIDNEY

POLYCYSTIC KIDNEY DISEASEPOLYCYSTIC KIDNEY DISEASE

RENAL CELL CARCINOMARENAL CELL CARCINOMA

RENAL TUBERCULOSISRENAL TUBERCULOSIS

NORMAL ADRENAL GLANDNORMAL ADRENAL GLAND

ADRENAL ADENOMAADRENAL ADENOMA

ADRENAL CARCINOMAADRENAL CARCINOMA

PHEOCHROMOCYTOMA PHEOCHROMOCYTOMA

GASTROINTESTINAL TRACTGASTROINTESTINAL TRACT

NORMAL ESOPHAGUSNORMAL ESOPHAGUS

ESOPHAGEAL ESOPHAGEAL ADENOCARCINOMAADENOCARCINOMA

ESOPHAGEAL PERFORATIONESOPHAGEAL PERFORATION

GASTRIC WALLGASTRIC WALL

GISTGIST

GASTRIC GASTRIC ADENOCARCINOMAADENOCARCINOMA

GASTRIC LYMPHOMAGASTRIC LYMPHOMA

SMALL BOWEL LYMPHOMASMALL BOWEL LYMPHOMA

COLON CARCINOMACOLON CARCINOMA

MULTISEGMENTAL CROHN MULTISEGMENTAL CROHN COLITISCOLITIS

ULCERATIVE COLITISULCERATIVE COLITIS

CT COLONOGRAPHYCT COLONOGRAPHY

CT IN BLUNT TRAUMA CT IN BLUNT TRAUMA ABDOMENABDOMEN METHOD OF CHOICE INITIAL METHOD OF CHOICE INITIAL

EVALUATION IN HEMODYNAMICALLY EVALUATION IN HEMODYNAMICALLY STABLE AND UNSTABLE TRAUMASTABLE AND UNSTABLE TRAUMA

ACCURACY IN DIAGNOSIS IS 97%ACCURACY IN DIAGNOSIS IS 97% ALSO EVALUATE EXTRA-ABDOMINAL ALSO EVALUATE EXTRA-ABDOMINAL

INJURIESINJURIES ROLE OF MDCT.ROLE OF MDCT.

INDICATIONSINDICATIONS

IN THE PAST-INDICATED FOR ONLY IN THE PAST-INDICATED FOR ONLY HEMODYNAMICALLY STABLE PATIENTS HEMODYNAMICALLY STABLE PATIENTS AND ASSOCIATED INJURIESAND ASSOCIATED INJURIES

RECENTLY INCREASINGLY USED IN RECENTLY INCREASINGLY USED IN UNSTABLE PATIENTSUNSTABLE PATIENTS

ADVANTAGE OF CT OVER DPLADVANTAGE OF CT OVER DPL ADVANTAGE OF CT OVER FAST.ADVANTAGE OF CT OVER FAST. CT LARGELY REPLACED CT LARGELY REPLACED

RADIONUCLEOTIDE RADIONUCLEOTIDE SCINTIGRAPHY,ANGIOGRAPHY AND USG.SCINTIGRAPHY,ANGIOGRAPHY AND USG.

HEMOPERITONEUMHEMOPERITONEUM

SPLENIC LACERATIONSPLENIC LACERATION

LIVER LACERATION AND LIVER LACERATION AND HEMATOMAHEMATOMA

PANCREATIC LACERATIONPANCREATIC LACERATION

RENAL LACERATIONRENAL LACERATION

INTERVENTIONAL CTINTERVENTIONAL CT

Therapeutic and diagnosticTherapeutic and diagnostic Image guided procedures can also be done Image guided procedures can also be done

under fluoroscopic, ulrasonographic and MRI under fluoroscopic, ulrasonographic and MRI guidedguided

CT provides precise, three dimensional CT provides precise, three dimensional localisationlocalisation

Can used in presence of open Can used in presence of open wounds,dressings,ostomies etcwounds,dressings,ostomies etc

DIAGNOSTIC INTERVENTIONAL DIAGNOSTIC INTERVENTIONAL CTCT PERCUTANEOUS BIOPSY OF LIVER, PERCUTANEOUS BIOPSY OF LIVER,

PANCREAS, ADRENAL PANCREAS, ADRENAL GLAND,RETROPERITONEUM,PARATHYGLAND,RETROPERITONEUM,PARATHYROIDROID

COMPLICATIONS ARE INFREQUENT COMPLICATIONS ARE INFREQUENT AND GENERALLY MINOR.AND GENERALLY MINOR.

THERAPEUTIC THERAPEUTIC INTERVENTIONAL CTINTERVENTIONAL CT DRAINAGE PROCEDURESDRAINAGE PROCEDURES PERCUTANEOUS NEPHROSTOMYPERCUTANEOUS NEPHROSTOMY CECOSTOMYCECOSTOMY NEUROLYSISNEUROLYSIS TUMOR ABLATION-CHEMICAL TUMOR ABLATION-CHEMICAL

-THERMAL-THERMAL

NEUROLYSISNEUROLYSIS

WHAT’S NEW IN CT? WHAT’S NEW IN CT?

VIRTUAL ENDOSCOPYVIRTUAL ENDOSCOPY

-IMAGING PERFORMED VIA CT TO PRODUCE -IMAGING PERFORMED VIA CT TO PRODUCE THREE DIMENSIONAL IMAGESTHREE DIMENSIONAL IMAGES

-USED TO DIAGNOSE DIVERTICULOSIS,POLYPS -USED TO DIAGNOSE DIVERTICULOSIS,POLYPS AND MALIGNANCYAND MALIGNANCY

-PROCEDURE-PROCEDURE

-OPTICAL COLONOSCOPY HAS BECOME GOLD -OPTICAL COLONOSCOPY HAS BECOME GOLD STANDARD IN SCREENING OF COLORECTAL STANDARD IN SCREENING OF COLORECTAL CANCERS.CANCERS.

ADVANTAGES-ADVANTAGES- -MORE COMFORTABLE-MORE COMFORTABLE -NO SEDATION -NO SEDATION -MORE DETAILED -MORE DETAILED EVALUATIONEVALUATION -TAKES LESSER TIME -TAKES LESSER TIME

DISADVANTAGES-DISADVANTAGES---EXPOSURE TO RADIATIONEXPOSURE TO RADIATION-SMALLER LESIONS NOT PICKED UP-SMALLER LESIONS NOT PICKED UP-BIOPSY CAN’T BE TAKEN-BIOPSY CAN’T BE TAKEN

COMPOSITE CT-PET SCANCOMPOSITE CT-PET SCAN

PROVIDES BOTH FUNCTIONAL AND PROVIDES BOTH FUNCTIONAL AND ANATOMIC IN SINGLE IMAGING ANATOMIC IN SINGLE IMAGING STUDY.STUDY.

In the FutureIn the Future

Still a larger role for ct over next decadeStill a larger role for ct over next decade MRI provided further stimulusMRI provided further stimulus Multislice CT imagers take center stageMultislice CT imagers take center stage Image manipulation will become easierImage manipulation will become easier Computer assisted diagnosis will become more Computer assisted diagnosis will become more

commoncommon Still be need for understanding of principles of Still be need for understanding of principles of

CT CT

ConclusionsConclusions CT is not very exciting from a physics point of CT is not very exciting from a physics point of

view (… didn’t you think the Saha chapter on CT view (… didn’t you think the Saha chapter on CT was facinating?)was facinating?)

However, it is the most popular “modern” However, it is the most popular “modern” imaging technique: available at over 30,000 imaging technique: available at over 30,000 world locations, including over 6,000 health care world locations, including over 6,000 health care centers in the US (many with multiple CT centers in the US (many with multiple CT machines) machines)

New uses of CT are constantly being developed. New uses of CT are constantly being developed. Recently, smaller CT setups are being used in Recently, smaller CT setups are being used in the OR to evaluate surgeries as they progress. the OR to evaluate surgeries as they progress. Better computer techniques will also enhance Better computer techniques will also enhance the value of CT studies.the value of CT studies.

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