REPOST: Dr. Re: scan @ 48 vs. 24 hrs. --> Ali

[Guest guest]

" Scanning later increases the ability to detect abnormal tissue, not because

more

gets into the thyroid tissue, but because less is in the surrounding tissue. "

(Dr. )

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(Dr. )

Date: Sat, 13 May 2000 07:41:19 -0400

Subject: Re: Scan procedure question

Diane,

When you are given a dose of radioiodine for scanning, the dose is taken up by

thyroid tissue and thyroid cancer rapidly. Much of the uptake is done within 4

hours. However, the dose also distributed in the rest of the body such as the

blood and tissue fluid surrounding the thyroid tissue.

The reason for waiting 2-3 days is to let the urinary excretion of radioiodine

eliminate background radioactivity from the blood and non-thyroidal tissues

while the radioiodine in the thyroid tissues is essentially stuck. This leads to

increased contrast between normal and abnormal sites. If you scan too early the

difference in uptake between normal and abnormal areas may be too low to detect.

Scanning later increases the ability to detect abnormal tissue, not because more

gets into the thyroid tissue, but because less is in the surrounding tissue.

You are correct that most of the dose is gone from your body at the time of

imaging. Successful imaging and successful therapy is often based on 1-2% of the

dose doing the " work " and 98-99% of the dose being excreted.

So scans done earlier (1 day after a dose) detect less cancer than scans done

later (3 days after a dose).

Jeff

Diane & Rob Blaszka wrote:

> I had a thought today as I was driving my car and reflecting on this thyca

> journey. It seems like a lot of annual scans miss things that are later

> picked up by other tests. Common scanning practice is to give patients 2-5

> mci and then scan 2 or 3 days later. Due to the half-life and quickly

> diminishing RAI, isn't most of it gone by the time the scan rolls around?

> Believe me, I want to trust my clean scans. But it just seems odd to me that

> they wait (in my case, I usually take the pill on Friday and scan on

> Monday) -- and I know the scans tend to miss things a bit too often. Maybe

> Ian, one of the doctors or someone can clarify? Thanks! (I really have to

> stop thinking as I drive.)

> -- Diane, TT 11/8, pap with lymph mets, 128 mci RAI 1/99, bit of dirt, 2

> clean scans since but some swollen neck nodes I fret about.

--

A. , MD

Nuclear Medicine, A-72 (Fax)

Albany Medical Center (Beeper)

Albany, NY 12203 cooperj@...

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At 12/17/2002 11:18 PM, you wrote:

>Hi folks. I am about to do my 1 year follow-up scan after last

>November's radiation. I believe that standard protocol for this is to

>receive the tracer dose and return the next day for the scan.

>Because of scheduling issues with the hospital, i am scheduled to

>take the dose and then come back 48 hours later. I was wondering if

>anybody has done their scan 2 days after the dose? I'm afraid of a

>scan with decreased accuracy if the radioactive iodine has already

>started to leave my body. Any thoughts would be appreciated.

>

>Thanks,

>Ali

>PT 8/01

>TT 9/01

>RAI 11/01

>off meds for tracer 12/24 and scan 12/26