Radionuclide Scanning

A

INVESTIGATIONS-

• USG- IOC (>4cm)
• Biliary radionuclide scan- no filling after 4 hours indicated obstructed cystic duct.
• HIDA/ PIPIDA scan- gold standard investigation

• Ans.D
• Gallium-68 somatostatin receptor positron emission tomography (PET) has been used in the diagnosis of neuroendocrine tumors (NETs). The compounds often used in molecular imaging of NETs with PET are 68Ga-DOTATOC, 68Ga-DOTATATE, and 68Ga-DOTANOC. There is a varying affinity to different somatostatin receptors.
• C11 Methionine PET is done for the brain tumor.
• 99mTc pertechnetate for a thyroid nodule, ectopic gastric mucosa 
• 18F-NaF PET is done for bones.

• The localization ability of Technetium 99m sestamibi scintigraphy is based on its preferential uptake by parathyroid cells, due to their high mitochondrial activity.
• Delayed images taken 2 to 3 h after injection are sensitive in up to 90% of single adenoma cases, with over 90% specificity. 
• Sestamibi imaging is also effective in cases of double adenoma. 
• However, it has significantly reduced accuracy in cases of four-gland hyperplasia.

D i.e. DTPA scan

• Antegrade pyelography (AP) & retrograde pyelography (RP) are invasive techniques. Percutaneous AP done by puncturing the collecting system & injecting contrast is rarely performed for diagnostic imaging purpose as ultrasound or CT may be used to visualize the ureter even in presence of abnormal renal function. However the indications of AP may be percutaneous nephrostomy (Whitaker test), to obtain renal urine for cyto/bactero-logical examination, to pinpoint obstruction level in dialated urinary system not adequately opacified by IVU/or after failed RP.

Retrograde ureteropyelography (RP) is valuable when (IVU/IVP) is suboptimal owing to poor renal function & in cases where IV contrast administration is contraindicated. Intravenous

urography/pyelography (IVU/IVP) is intravenous administration of iodinated contrast and taking renal x-rays. It is initial technique in evaluation of possible urinary obstruction. For taking additional radiographs rule of 8 (i.e. if no contrast appears in collecting system by 15 min after injection, there is a little reason to obtain next film until 2 hours (=15×8) later) prevent multiple exposure. There has been a significant decline in use of IVU as dominant imaging technique in obstruction d/ t fear of contrast induced nephrotoxicity and d/ t growth of renal sonography & low dose CT. The main draw back of IVU is that it is time consuming.

• Conventional gray scale sonography is good screening method for detecting subacute and chronic obstruction as demonstrated by pyelocaliectasis however, in acute obstruction pyelocaliectasis is minimal or absent. Another drawback is its inability to realibly distinguish mild hydronephrosis from normal or prominent extrarenal pelvis. Duplex & color Doppler ultrasound have yielded advances in:

– distinguishing mild pyelectasis from prominent central renal blood vessels.

–  detecting high grade acute ureteric obstruction through analysis of ureteral jets (normal ureteral jets i.e. ejection of urine from ureter into urinary bladder are bilaterally symmetrical).

–   estabilishing renal resistive index (RI) as an independent hemodynamic measure of urinary obstruction.

CT scan has emerged as an effective imaging tool in evaluation of acute renal obstruction esp in screening patients with acute flank pain / azotemia who are strongly suspected as having obstruction and in establishing the etiology of ureteral obstruction when other investigations have failed. Non contrast low dose CT is very quick & useful in determining the presence or absence of obstruction and have higher sensitivity for detection of ureteric stones as compared to IVU.

The radionale for CT urography is that high risk patients or patients with hematuria can be fully investigated by a single imaging technique with a high degree of sensitivity & specificity. The major disadvantage is the radiation dose of CTU which is upto 5 times higher than IVU.

• Radionuclide renography has limited role in evaluation of acute obstruction as it lacks precise anatomical delineation of obstruction as well as ability to define the cause of obstruction. Its major use is in differentiation of a dilated non obstructed system from a partially obstructed system. When IVU demonstrates a dilated collecting system and there is doubt about the presence or absence of obstruction diuresis (frusemide) renography with Tc99 DTPA or MAG-3 will usually help to distinguish obstructive from non-obstructive dilatation & will localize the site of obstruction. The collecting system activity washes out with in 10minutes in non obstructive after diuresis challenge but no or partial response is seen in obstructive cases. Measurement of differential renal function can be made during diuresis renography or as a separate procedure using Tc99 DMSA examinationQ.

MR urography is an ideal technique in pregnancy, where there is contrast allergy, renal failure patients & if radiation dose is an issue. The level of obstruction is always identified however ureteric abnormalities (if < 4mm) are poorly defined & that includes stones.

A i.e. Tc-Thallium Substraction Scan

A i.e. Radionuclide scanning

Ans. is ‘b’ i.e., Radiolabelled, erythrocyte scanning 

Ans is ‘d’ ie. Radionuclide scan 

“If a Meckels diverticulum is suspected because of repeated gastrointestinal haemorrhage the abdomen can be scanned after the injection of ⁹⁹Tc-labelled pertechnetate intravenously. This may localise heterotopic gastric mucosa revealing the site of a meckels diverticulum in 90% of cases.” – Bailey & Love

Answer is C (Thallium scan)

Reversible Myocardial Ischemia can be detected by myocardial perfusion imaging using compounds labeled with thallium- 201 (Thallium Scan).

Ans: A i.e. Tc-99m linked to methylene diphosphonate (99m Tc-MDP)

• Tc-99m linked to methylene diphosphonate (99m Tc-MDP) is used in bone imaging
• Tc-99 pyrophosphate is used for defining hot spots in myocardial infarction/avid infarct imaging
• 99m Tc-Sc is used in imaging of reticuloendothelial system (liver/ spleen), gastric emptying, GI bleeds
• Gallium 67 is used for tumours/abscess

Ans. C: Both of the above

A gamma camera/scintillation camera/ Anger camera is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development and nuclear medical imaging to view and analyse images of the human body or the distribution of medically injected, inhaled, or ingested radionuclides emitting gamma rays. Scintigraphy is the use of gamma cameras to capture emitted radiation from internal radioisotopes to create twodimensional images.

SPECT (single photon emission computed tomography) imaging, as used in nuclear cardiac stress testing, is performed using gamma cameras, usually one, two or three detectors or heads, are slowly rotated around the patient’s torso. Multi­headed gamma cameras can also be used for Positron emission tomography scanning. Gamma camera PET is markedly inferior to PET imaging with a purpose designed PET scanner, as the scintillator crystal has poor sensitivity for the high-energy annihilation photons, and the detector area is significantly smaller. However, given the low cost of a gamma camera and its additional flexibility compared to a dedicated PET scanner, this technique is useful where the expense and resource implications of a PET scanner cannot be justified.

Ans. D: Technetium-99m linked to Methylene diphosphonate

Scans used for:

• Hot spot in MI: Technetium scan
• Pancreatic scanning: Selenium 75
• Parathyroids: Sestamibi scan
• Renal GFR estimation: Tc 99DTPA scan
• Vesicourethral reflex: MAG3 Tc 99 scan
• Thyroid scan: 1-131

Ans. A: Technetium-99 scan

Ultrasound is the preferred imaging modality for thyroid nodules, and the ultrasound guided fine needle aspiration biopsy (FNAB) is the preferred method of tissue. 

Ans. Quantity of radionuclide disintegrating per second

Ans. DTPA scan

Ans. Technetium-thallium subtraction scan

Ans. Technetium-99m linked to Methylene dis-phos-phonate (99mTc-MDP)

Ans. DTPA