At what point should I have an MRI to see if I might be getting dementia?

When my mom had a MRI, it showed atrophy that was probably age related and did not confirm or deny her dementia.

I would start with talking to your doctor and getting some blood work done. As mentioned, there are some things that can lead to confusion like low B12, thyroid issues, etc. Certain meds can cause issues, like cholesterol meds, some BP meds. How are you sleeping? If you're sleep deprived, that doesn't help.

I would google things to do to increase brain power. I'd start some supplements. Improve your diet. Increase exercise. Lose weight, if you happen to be a bit overweight. Brain games. Don't worry too much and take some positive action to help you feel better.

My hubs can;t believe I can't just come up with phone numbers..even his or DDs cell phone # Heck half the time I can't remember mine! Because they are all stored on my phone so I never have to recall them! To me that is just something I don;t have to worry about. But I can tell you the plot of a book I read, or medical info I need to use daily. Maybe I am lazy,, LOL,, but I sort of look at some technology as a "space saver" for my mind. And like FF says,, stuff pops into my mind later!

Jobaby, when my doctor put me on cholesterol medicine, I stopped taking it a few days later as I noticed my short term memory was having a field day. After a few days off said meds my memory was back to normal. I will try diet instead of the meds.

One needs to remember our brain is like a bunch of filing cabinets and it becomes full as we learn more and more over the years. Thus, if we need information [such as the right word to use] it will take longer to find it in the brain's filing cabinet. And sometimes info is misfiled.

Any time hubby and I can't remember someone name, we just chuckle about it because soon enough it will pop into our mind, or at midnight :)

Not remembering a word isn't dementia. It's more like when you start asking the same question multiple times in a hour and not remembering the other times you asked it or the answer.

In short, when you develop dementia, you'll likely be the last one to notice.

Try to put your family members' experiences out of your mind and live your life.

MRIs don't show most dementias. They can diagnose some things, but autopsies are the way to diagnose dementia for certain, and you sure aren't ready for that.
You are mentioning things common to most people of any age, and certainly to anyone with any amount of anxiety, and things that are very common in any aging or beset brain. You haven't mentioned anything worrisome.
Now, if you are, say, putting the butter in the sock drawer and the socks in the refrig, it is worth looking into if it happens too much. If you leave your home for a walk and suddenly wonder where you are, how to get home? Worth worrying about.
Can you spell Forum backwards?
Can you draw a clock and set it for 11:15?
We all commonly forget names.
Things like balance and memory decrease with age. But Alzheimer's and other dementias are a "make no mistake" sort of thing.
Look up some simple tests online and see how you do on them. Ask friends to let you know if they see things that are different than they think they should be. And, by all means, see the doc. I am thinking he or she is going to tell you that you are suffering from anxiety and normalacy. But that's just my guess.
Very best of luck. I am 80. I can't tell you how long it took me to remember hydrangea and nasturtium the other day. And answering a post here I wished someone "Peach" instead of peace, so there you are. Stuff happens.

Stress and grief can do a number on the brain/mind so don't get too alarmed. But definitely talk to your doctor, there are assessments that can be done before a MRI is ordered.

In the meantime, give attention to your hydration, nutrition, and sleep along with finding ways to decompress from all that's going on.

"...ancillary imaging studies (eg, computed tomography [CT]; magnetic resonance imaging [MRI]; single-photon emission CT [SPECT]; or positron emission tomography [PET]) and laboratory tests may be used. These tests help exclude other possible causes for dementia (eg, cerebrovascular disease, cobalamin [vitamin B12] deficiency, syphilis, thyroid disease)."

source: https://emedicine.medscape.com/article/1134817-workup

In other words, imaging mostly just tells the doctor that your dementia symptoms are not being caused by other problems (like a brain tumor, for instance). There is no real definitive or predictive test for dementia. Also, unless a doctor actual orders an MRI for this purpose, you probably won't be able to have an MRI, and even if you could request it, Medicare won't pay for it.

The best thing is to get a simple baseline cognitive/memory test from your primary doctor (repeat back 3 words after 10 minutes, draw a clock face with whatever time they tell you, etc.). Ask for this test at every annual check-up or whenever you have truly worrisome symptoms.

Some dementias are genetic but you still need to inherit the gene to develop it. In other words, if one or both of your parents had it, you are at higher risk to get it, but you still must inherit the gene...and maybe you won't inherit it. Your sibling could inherit it, but not you. It's a crap-shoot. I live off of Post-it notes and some days I can hardly remember some really common words. I'm 63 and a copywriter, so I'm exercising my language skills every day, yet I still have problems with word recollection from time to time. It's just part of our aging brains.

Keep in mind there is no cure or any real treatment to slow down dementia. The best thing you can do is live cleanly and respect your body -- and plan/prepare for your age-related decline (choosing a PoA, writing up a Living Will and a Last Will, being realistic about "aging gracefully" or aging-in-place, financial planning for your care, etc.)